Tag Archives: dBASE III

Early days of Clipper

Posted on by vivaclipper

Notes on early days of Clipper

Some quotations :

Clipper was originally built in 1985 as a compiler for dBASE III.

Clipper was built by Nantucket Corporation led by Barry ReBell (management) and Brian Russell (technical), and  later sold to …

Source

         ~~~~~~~~~~~~~~~~~~~

Brett Oliver, Jim Warner, Brian Russell, Richard McConnell …

Main architects and primary developers of Clipper and founders of Nantucket Corporation. It was 1984 when
Clipper was born.

Source

~~~~~~~~~~~~~~~~~~~

Clipper Summer’87 Manual, “Credits” page :

ClpSum87Credits

~~~~~~~~~~~~~~~~~~~

Clipper 5.0 Manual, “Credits” page :

Clp5.0Credits

~~~~~~~~~~~~~~~~~~~

… and 30 years after birth of this phenomenal myth, one (or first) of main builders suddenly appeared : Brett Oliver !

By a comment to one page of this blog :

Not only main starter / builder of Clipper, he is also author of wonderful books :

Clipper Programming: An In-Depth Introduction to Programming

This book also is a myth.

And he told me on request, something on beginning and building story of this great myth;

Brian was working at Ashton-Tate, as was I.

I was in tech support, alongside Brian, and customers that were phoning in kept asking for a compiler.

So I approached Barry for the money to back it. He had a temp agency. I met him in the Ashton-Tate cafeteria.

I recruited Brian at lunch at a Japanese restaurant in Culver city.

Clipper was the first program Brian had written in ‘C’.

He learned C as he programmed Clipper.

I asked him when I was recruiting him if he had ever written a compiler.

He said he had written a Pascal compiler in university. (He later admitted that it had never worked!).

The first development office was a beach house in Malibu.

Tom Rettig was the editor for dNEWS at Ashton-Tate. I took over as editor of dNEWS.

I was the first VP of sales, and one of my employees was Mary Beth. I introduced her to Brian and later they married.

At the first Comdex in Vegas, Brian was upstairs in his room – coding.

He got one command to work – paint a dot on the screen. We demonstrated that one command, and showed that we could draw a box 20 times faster than dBASE.

I wrote a couple of books on Clipper, and was also on the dBASE for Windows development team at Borland. 

I worked with Tom at his condo in Santa Monica for a time. Too bad he died.

Barry died in 2009.

Brian and I went dirt biking together. He loaned me his street bike for a couple of months when my car was getting fixed. He is a good guy. I think he is working in LA.

We live in San Diego, – my wife is from Liechtenstein. We have three boys.

I am Scottish. Currently programming in eCommerce.

Anyway, nice chatting.

Stay in touch.

I wish he will write more …

C5DG-7 DBFNTX Driver

Posted on by vivaclipper

Clipper 5.x – Drivers Guide

Chapter 7

DBFNTX Driver Installation and Usage

DBFNTX is the default RDD for Clipper. This new database driver replaces the DBFNTX database driver supplied with earlier versions of Clipper and adds a number of new indexing features. With DBFNTX, you can:

. Create conditional indexes by specifying a FOR condition

. Create indexes using a record scope or WHILE condition, allowing you to INDEX based on the order of another index

. Create both ascending and descending order indexes

. Specify an expression that is evaluated periodically during indexing in order to display an index progress indicator

In This Chapter 

This chapter explains how to install DBFNTX and how to use it in your applications. The following major topics are discussed:

. Overview of the DBFNTX RDD

. New Locking Scheme

. Conditional Indexing

. Installing DBFNTX Driver Files

. Linking the DBFNTX Driver

. Using the DBFNTX Driver

. Compatibility with dBASE III

Overview of the DBFNTX RDD

As an update of the default database driver, DBFNTX is linked into and used automatically by your application unless you compile using the /R option.

New Features

The replaceable driver lets you create and maintain (.ntx) files using features above and beyond those supplied with the previous DBFNTX driver. The new indexing features are supplied in the form of several syntactical additions to the INDEX and REINDEX commands. Specifically you can:

. Specify full record scoping and conditional filtering using the standard ALL, FOR, WHILE, NEXT, REST, and RECORD clauses

. Create an index while another controlling index is still active

. Monitor indexing as each record (or a specified record number interval) is processed using the EVAL and EVERY clauses

. Eliminate separate coding for descending order keys using the DESCENDING clause

Compatibility

Index files (.ntx) created with the original DBFNTX driver are compatible with DBFNTX and can be used in new applications without reindexing. Index files (.ntx) created with this version of DBFNTX will also work with previous Clipper applications provided that you use no FOR, WHILE, <scope>, or DESCENDING clauses.

Important! Indexes produced with DBFNTX using FOR or DESCENDING are incompatible with earlier version (.ntx) files. If you attempt to access them with the original DBFNTX database driver or programs compiled with versions earlier than Clipper 5.2, you will get an unrecoverable runtime error. In Clipper, this generates an “index corrupted” error message, causing the application to terminate.

New Locking Scheme

The DBFNTX database driver implements a new locking scheme to resolve several problems identified in previous versions of Clipper and to prevent potential problems that might arise when running Clipper applications in a network environment. This section discusses these changes and their implications, including compatibility issues.

Lock Time-outs

Problem: Index locking in previous versions of Clipper was handled automatically by the database driver, and had no time-out provision. This created the potential for problems in network environments if a workstation died while holding a lock. If this situation occurred all other workstations waiting for an index lock would appear to freeze while waiting to obtain their lock. This could also happen if a user placed a Clipper application in the background on a multitasking system without sufficient processing time allocated to it. Eventually, most network operation systems would clear a connection that had no activity for a specified period of time. This would free the lock and everything would resume as normal, but frustrated users may have rebooted their machines possibly causing file corruption.

Solution: In Clipper 5.2 the NTX driver will generate a recoverable runtime error if it fails to lock the index after a predetermined number of retries. The default error handler for this system simply returns (.T.) to retry the operation. This emulates the behavior of previous Clipper versions.

Error Handling

Time out handling: The handling of this error is problematic because the lock is issued from various internal index routines. Therefore the only safe recoveries are to retry or quit. Choosing to default from the error or issuing a break will more than likely leave the index in a corrupted state. If either of the options is employed, the application should immediately recreate the index. The preferred way to handle a time out such as this is to alert the user of the situation so they don’t think their machine has hung, and then have the network administrator determine what workstation is causing the problem. When the problem workstation is cleared, the users that have timed out can select retry and continue processing.

NTXERR.PRG: The file NTXERR.PRG contains the source code for the default error handler INIT procedure. This error handler can be modified to allow user-defined error handling for index lock time-outs. Care should be exercised when modifying the error handler as detailed above.

Compatibility: The lock time-out capability when used in conjunction with the default error handler is totally compatibility with previous versions of Clipper. No changes are made to the NTX file structure and no action is required by the developer to activate the time-out functionality.

New Lock Offset

Problem: Index locking, which is transparent to the developer, uses a single-byte semaphore locking system. This semaphore was placed at a virtual offset (beyond the physical end of file) in the index file. In previous versions of Clipper, this offset was located at one billion (1,000,000,000) which was adequate at the time. But many systems today are capable of producing indexes that are large enough to cause the actual data present at the lock offset to become physically locked. This leads to problems when trying to read or write to the data at that offset.

Solution: The solution is to move the offset where locking occurs to a location at a greater offset. We have chosen FFFFFFFF hex, which is the largest offset possible under the DOS operating system. The problem with this solution is that new applications using the index will be locking this new byte while old applications using the same index will lock the old position. Clearly this would cause both applications to fail because each could have a lock on the file at the same time.

To avoid this, the signature of the index (in the index header) is modified to prevent pre-Clipper 5.2 applications from being able to open the index. Clipper 5.2 applications can detect the correct offset to use by the flag in the header and will automatically use the correct one. In Figure 7-1 below, each bit represents a flag:

BIT  7 6 5 4 3 2 1 0
FLAG R R R O P I I C
R Reserved
I Index type - both bits set (NTX)
C Index created with a Condition, condition in header
T Created as a Temporary index
O New Offset for exclusive (semaphore) lock
Figure 7-1: Bit Field for the Signature Byte of a -Clipper 5.2 NTX File

Activation

If Clipper 5.2 automatically modified the signature in the header when it created indexes, programs with automatic reindexing routines would be creating indexes that appeared corrupt to pre-Clipper 5.2 applications. This has an obvious problem with backward compatibility. Therefore, in order to create indexes with the new signature, the developer must link in the module NTXLOCK2.OBJ with the full knowledge that this will create indexes that older applications will not be able to access.

Header Changes

The signature byte of a .NTX file is 6 for an unenhanced NTX index. The inclusion of the NTXLOCK2.OBJ will cause the signature to become 26 hex. (6 hex ORed with 20 hex). See Figure 7-1 for an illustration of all the possible values for the signature byte.

Error Handling

Clipper 5.2 applications will automatically recognize the signature byte of the header, and depending on the signature value, will use the correct index lock location. Applications built with previous versions of Clipper, however, do not have the capability to detect the optional new information in the signature byte. Therefore, when an order application tries to open a file that has been created with the NTXLOCK2.OBJ linked in it will produce a Corruption Detected error.

Compatibility

The new locking location, if used, is not backward compatible with applications compiled with previous versions of Clipper.

Indexes created by applications built with a previous version of Clipper can be used by Clipper 5.2 using the new location and will not be modified unless the index is recreated in application.

Since older applications have no knowledge of the new index locking scheme nor of the significance of the header signature, these applications will assume the index is corrupt and will produce an Index Corrupted error.

Conditional Indexing

Conditional indexes are a feature of the DBFNTX driver. This section discusses this feature of the DBFNTX driver in some detail, giving you specific information about the implementation of conditional indexes. Compatibility issues are also discussed.

Conditional Indexes

Conditional indexes are produced by using a FOR condition in the index creation process. These indexes are made fully maintainable by storing the FOR condition in the index header. This condition is subsequently retrieved and compiled each time the index in opened. During updates, items are added to the index only if they meet the criteria of the condition.

Since older applications do not have the ability to recognize and use the condition stored in the header, they must be prevented from opening the index since they corrupt the index. This is accomplished by modifying the signature of the index (in the index header) preventing pre-Clipper 5.2 applications from being able to open the index. Clipper 5.2 applications can detect the flag in the header and will automatically use the stored FOR condition correctly.

Temporary Indexes

Temporary indexes are produced by using any scoping clause other than the FOR condition in the index creation process. These indexes are not automatically maintainable because the condition is not stored for later use. These indexes can be made maintainable if the condition can be expressed as a FOR condition and is added using the FOR clause. But the main use of temporary indexes is for fast creation of indexes for read- only browses or reports that operate on a subset of the database.

Since older applications would not operate properly with indexes that do not contain all the keys in a given database, they must be prevented from using them. This is accomplished by modifying the index signature to prevent pre-Clipper 5.2 applications from being able to open the index.

Activation

Conditional Indexes

The developer need only specify the FOR condition when creating the index. In doing so he must be fully aware the index will no longer be accessible to pre–Clipper 5.2 applications.

Temporary Indexes

The developer need only specify a scope other than FOR when creating the index. In doing so he must be fully aware the index will no longer be accessible to pre-Clipper 5.2 applications and that the index created is not maintainable.

Header Changes

The signature byte of a .NTX file is 6 for a unenhanced NTX index. If the index is created as a conditional index it will have a signature of 7 hex (6 hex ORed with 1 hex). If the index is created as a temporary index it will have a signature of E hex. (6 hex ORed with 8 hex). See Figure 7-1 for an illustration of all the possible values for the signature byte.

Error Handling

Corruption Detected

Since older applications have no knowledge of the new index features nor how to interpret the additional flags in the header signature, these applications will assume the index is corrupt and will produce an Index Corrupted error.

EOF()

If an index is created with a FOR condition and an attempt is made to update the index with a key that does not match the condition, the update is suppressed and the index is placed at EOF(). This is consistent with the current behavior for indexes created with the unique flag when an update is attempted with a non-unique key.

Also if a navigational action is attempted (SKIP) and the current record is not found in the index, the index will place the record pointer at EOF(). This is true for both conditional and temporary indexes.

Compatibility

Backward Compatibility

If the conditional or temporary indexing features are used the index produced will not be backward compatible with applications compiled with previous versions of Clipper. Indexes that do not use the features, however, will be 100% compatible.

Forward Compatibility

Indexes created by applications built with a previous version of Clipper can be used by Clipper 5.2 and will not be modified unless the index is recreated using either the conditional or temporary index features.

Error Message Produced by Old Applications

Since older applications have no knowledge of the new index locking scheme nor of the significance of the header signature, these applications will assume the index is corrupt and will produce an Index Corrupted error.

Installing DBFNTX Driver Files

DBFNTX is supplied as the file DBFNTX.LIB.

The Clipper installation program installs this driver as the default in the \CLIPPER5\LIB subdirectory on the drive that you specify, so you need not install the driver manually.

Important! Before installing Clipper, you may want to rename the DBFNTX.LIB that currently resides in your \CLIPPER5\LIB directory to DBFNTX.001. The new version, when installed, will overwrite DBFNTX.LIB. If you do not rename or otherwise protect the old version of DBFNTX.LIB, you will lose it.

Linking the DBFNTX Database Driver

Since DBFNTX is the default database driver for Clipper, there are no special instructions for linking. Unless you specify the /R option when you compile, the new driver will be linked into each program automatically if you specify a USE command or DBUSEAREA() function without an explicit request for another database driver. The driver is also linked if you specify an INDEX or REINDEX command with any of the new features.

Using the DBFNTX Database Driver

In applications written for the new DBFNTX driver, you can use the INDEX and REINDEX commands exactly as you have used them in the past. The index files (.ntx) you create and maintain in this way are completely compatible with those created using previous versions of the driver.

Changes to existing code are necessary only if you use the new indexing features. The (.ntx) files you create using the new features will have a slightly different header file and cannot be used by programs linked with a previous version of the driver.

Using (.ntx) and (.ndx) Files Concurrently

You can use (.ntx) and (.ndx) files concurrently in a Clipper program like this:

// (.ntx) file using default DBFNTX driver

USE File1 INDEX File1 NEW

// (.ndx) files using DBFNDX driver

USE File2 VIA "DBFNDX" INDEX File2 NEW

Note, however, that you cannot use (.ntx) and (.ndx) files in the same work area. For example, the following does not work:

USE File1 VIA "DBFNDX" INDEX File1.ntx, File2.ndx

Compatibility with dBASE III PLUS

The default DBFNTX driver makes Clipper programs behave differently than traditional dBASE programs. Some of these differences are discussed below.

Supported Data Types

The DBFNTX database driver supports the following dBASE III PLUS- compatible data types for key expressions:

. Character

. Numeric

. Date

. Logical

Supported Key Expressions

When you create (.ntx) files using the DBFNTX driver, you can use all Clipper or user-defined functions compatible with dBASE III PLUS as well as other functions accepted by the extended Clipper functionality.

Error Handling

The indexing behavior of DBFNTX and DBFNDX in a Clipper application is identical unless otherwise noted. With the default DBFNTX driver, you can handle most errors using BEGIN SEQUENCE…END SEQUENCE as illustrated in the next section.

FIND vs SEEK

In Clipper, you can use the FIND command only to locate keys in indexes where the index key expression is character data type. This differs from dBASE III PLUS where FIND supports character and numeric key values.

Note: In Clipper programs, always use the SEEK command or the DBSEEK() function to search an index for a key value.

The DBFNTX driver lets you recover from data type errors raised during a FIND or SEEK. However, since Error:canDefault, Error:canRetry or Error:canSubstitute are set to false (.F.), you should use BEGIN SEQUENCE…END to handle such SEEK or FIND data type errors. Within the error block for the current operation, issue a BREAK() using the error object that the DBFNTX database driver generates, like this:

bOld := ERRORBLOCK({|oError| BREAK(oError)})
 .
 .
 .
 BEGIN SEQUENCE
     SEEK xVar
 RECOVER USING oError
     // Recovery code END
 .
 .
 .
 ERRORBLOCK(bOld)

There is an extensive discussion of the effective use of the Clipper error system in the Error Handling Strategies chapter of the Programming and Utilities guide.

Sharing Data on a Network

The DBFNTX driver provides file and record locking schemes that are different from dBASE III PLUS schemes. This means that if the same database and index files are open in Clipper and in dBASE III PLUS, Clipper program locks are not visible to dBASE III PLUS and vice versa.

Warning! Database integrity is not guaranteed and index corruption will occur if Clipper and dBASE III PLUS programs attempt to write to a database or index file at the same time. Therefore, concurrent use of the same database (.dbf) and index (.ndx) files by dBASE III PLUS and Clipper programs is strongly discouraged and not supported by Computer Associates.

Summary

In this chapter, you were given an overview of the new features of the default DBFNTX RDD. You learned how to this driver is automatically linked and how to use it in your applications, and were given an overview of the compatiblity issues.

C5DG-6 DBFNDX Driver

Posted on by vivaclipper

Clipper 5.x – Drivers Guide

Chapter 6

DBFNDX Driver Installation and Usage

DBFNDX is the dBASE III PLUS compatible RDD for Clipper. The DBFNDX driver uses the Clipper driver architecture to access dBASE III PLUS compatible index files within a Clipper program.

In This Chapter

This chapter explains how to install DBFNDX and how to use it in your applications. The following major topics are discussed:

. Overview of the DBFNDX RDD

. Installing DBFNDX Driver Files

. Linking the DBFNDX Driver

. Using the DBFNDX Driver

. Compatibility with dBASE III PLUS

Overview of the DBFNDX RDD

The DBFNDX database driver allows creation, access, and updating of dBASE III and dBASE III PLUS compatible index (.ndx) files. Index files (.ndx) created with Clipper are exactly the same as those created by dBASE III PLUS. All operations that can be performed on standard Clipper index (.ntx) files can be performed on (.ndx) files using the DBFNDX database driver.

In a network environment, the DBFNDX driver supports the Clipper file and record locking scheme. The multiuser behavior is the same as the default DBFNTX driver. This means that the DBFNDX database driver supports concurrent access to (.ndx) files between Clipper applications only. Concurrent access to (.ndx) files between dBASE III PLUS and Clipper programs is not supported.

Important! Updating database (.dbf) and index (.ndx) files shared between dBASE III PLUS and Clipper programs may corrupt the (.dbf) and any of its associated (.ndx) files.

Installing DBFNDX Driver Files

The DBFNDX database driver is supplied as the file, DBFNDX.LIB.

The Clipper installation program installs this driver in the \CLIPPER5\LIB subdirectory on the drive that you specify, so you need not install the driver manually.

Linking the DBFNDX Database Driver

To link the DBFNDX database driver into an application program, you must specify DBFNDX.LIB to the linker in addition to your application object files (.OBJ).

1. To link with .RTLink using positional syntax:

C>RTLINK <appObjectList> ,,, DBFNDX

2. To link with .RTLink using freeformat syntax:

C>RTLINK FI <appObjectList> LIB DBFNDX

Note: These link commands all assume the LIB, OBJ, and PLL environment variables are set to the standard locations. They also assume that the Clipper programs were compiled without the /R option.

Using the DBFNDX Database Driver

To use (.ndx) files in a Clipper program:

1. Place a REQUEST DBFNDX at the beginning of your application or at the top of the first program file (.prg) that opens a database file using the DBFNDX driver.

2. Specify the VIA “DBFNDX” clause if you open the database file with the USE command.

-OR-

3. Specify “DBFNDX” for the <cDriver> argument if you open the database file with the DBUSEAREA() function.

-OR-

4. Use RDDSETDEFAULT(“DBFNDX”) to set the default driver to DBFNDX.

Except in the case of REQUEST, the RDD name must be a literal character string or a variable. In all cases it is important that the driver name be spelled correctly.

The following program fragments illustrate:

REQUEST DBFNDX 
. 
. 
. 
USE Customers INDEX Name, Address NEW VIA "DBFNDX"

-OR-

REQUEST DBFNDX RDDSETDEFAULT( "DBFNDX" ) 
.
.
. 
USE Customers INDEX Name, Address NEW

Using (.ntx) and (.ndx) Files Concurrently

You can use (.ndx) and (.ntx) files concurrently in a Clipper program like this:

REQUEST DBFNDX

// (.ntx) file using default DBFNTX driver USE File1 INDEX File1 NEW

// (.ndx) files using DBFNDX driver USE File2 VIA “DBFNDX” INDEX File2 NEW

Note, however, that you cannot use (.ndx) and (.ntx) files in the same work area. For example, the following does not work:

USE File1 VIA "DBFNDX" INDEX File1.ntx, File2.ndx

Compatibility with dBASE III PLUS

When accessing dBASE III PLUS (.ndx) files, there are several compatibility issues of which you must be aware. These issues are discussed below.

Supported Data Types

The DBFNDX database driver supports the following data types for key expressions:

. Character

. Numeric

. Date

This is consistent with dBASE III PLUS.

The DBFNDX database driver does not support indexing with logical key expressions as does the default DBFNTX database driver. This is actually a dBASE III PLUS limitation and is not supported by the DBFNDX driver in order to enforce compatibility with dBASE III PLUS.

To work around this limitation, index logical values by converting them to character values like this:

INDEX ON IIF(<lExp>, "T", "F") TO <logicalIndex>

Supported Key Expressions

When you create (.ndx) files using the DBFNDX driver, you must use only Clipper or user-defined functions compatible with dBASE III PLUS. Use of the other functions will render the (.ndx) file unreadable in dBASE III PLUS.

FIND vs SEEK

In Clipper, you can use the FIND command only to locate keys in indexes where the index key expression is character type. This differs from dBASE III PLUS where FIND supports character and numeric key values.

Note: In Clipper programs, always use the SEEK command or the DBSEEK() function to search an index for a key value.

The DBFNDX driver lets you recover from a data type error raised during a FIND or SEEK. However, since Error:canDefault, Error:canRetry, or Error:canSubstitute are set to false (.F.), you should use BEGIN SEQUENCE…END to handle a SEEK or FIND data type error. Within the error block for the current operation, issue a BREAK() using the error object the DBFNDX database driver generates, like this:

bOld := ERRORBLOCK({|oError| BREAK(oError)})
.
.
 .
BEGIN SEQUENCE
SEEK xVar
RECOVER USING oError
// Recovery code
END
.
.
 .
ERRORBLOCK(bOld)

There is an extensive discussion of the effective use of the Clipper error system in the Error Handling Strategies chapter of the Programming and Utilities guide.

Sharing Data on a Network

As mentioned above, the DBFNDX driver does not support dBASE III PLUS file and record locking schemes. Instead, the DBFNDX driver supports the DBFNTX file and record locking scheme. This means that if the same database and index files are open in Clipper and dBASE III PLUS, Clipper program locks are not visible to dBASE III PLUS and vice versa.

Warning! Database integrity is not guaranteed and index corruption will occur if Clipper and dBASE III PLUS programs attempt to write to a database or index file at the same time. For this reason, concurrent use of the same database (.dbf) and index (.ndx) files by dBASE III PLUS and Clipper programs is strongly discouraged and not supported.

Compatibility with dBASE IV

Specific compatibility with dBASE IV is provided through the DBFMDX driver. It includes (.dbf), (.mdx), and (.dbt) file format compatibility and is described in detail in the previous chapter.

Summary

In this chapter, you were given an overview of the features and benefits of the DBFNDX RDD. You learned how to link this driver and how to use it in your applications, and were given an overview of the compatibility issues.

C5DG-1 Introduction

Posted on by vivaclipper

Clipper 5.x – Drivers Guide

Chapter 1

Introduction

Important!

Some of the topics in this guide are intended for advanced Clipper developers. Much of this information is presented at a fairly high level and requires programming knowledge beyond the Clipper language. Other parts are useful to users of all levels. Refer to the “User Interface Levels” section of the Replaceable Database Driver Architecture chapter to determine which part of the language is appropriate to your level of expertise.

Based on your own experience level with the Clipper language, you should decide whether you wish to take advantage of these new and advanced features. The Reference guide contains existing Clipper command and function syntax and descriptions. This guide addresses new extensions to Clipper. Understanding this information should enable you to increase the power and effectiveness of your applications.

Clipper supports a driver architecture that allows Clipper- compiled applications to use replaceable database and terminal drivers. This Drivers guide contains all the information you need to use the replaceable drivers provided as part of the Clipper Development System.

Overview of RDD System

RDD is an abbreviation for Replaceable Database Driver, and it is used to describe an interface that controls how your application accesses and manipulates database and ancillary files.
Clipper provides several RDDs to give you access to the database, memo, and index file formats of many popular database software products. By simply linking the proper RDD with your application, you get automatic, easy access to files created by other database engines.

Moreover, Clipper gives you new and enhanced commands and functions designed to make your applications independent of the RDD in use. Using RDDs, you can give end users more flexibility in choosing to migrate to your Clipper applications without losing data and to easily move their data back and forth between applications if they prefer.

Overview of Alternate Terminal Drivers

An Alternate Terminal Driver is a library file (.LIB) that controls how your application addresses the screen output device. Clipper provides several Alternate Terminal Drivers to allow your applications to run in a wider variety of environments.

Note: To perform normal information presented in screen input/output in a Clipper application, you do not need the Drivers guide. The default database and terminal drivers are automatically linked and the commands and functions used for these purposes are discussed in the Reference guide. For several categorized lists of these commands and functions, refer to Appendix G: Categorized Language Tables in the Error Messages and Appendices guide.

In This Guide

This guide consists of nine chapters including this Introduction chapter.

For an online version of this guide accessible while operating your program editor or any other development utility, use The Guide To Clipper.

Chapter 2: Replaceable Database Driver Architecture

The Clipper database system supports a driver architecture that makes Clipper-compiled applications data format independent. Such applications can, therefore, access the data formats of other database systems, including the dBASE IV (.mdx), FoxPro (.cdx), and Paradox (.db) formats on a variety of equipment. This chapter discusses how RDDs fit into the overall Clipper architecture, defines the basic terminology you will need to understand subsequent chapters, and summarizes new and enhanced commands and functions designed to support the RDD architecture.

Chapter 3: Reference

Clipper 5.x provides many new and enhanced commands and functions that you will use to access and manipulate databases and to get specific information about the RDD in use. This chapter contains entries for all new Clipper commands and functions designed for use with RDDs. As for existing language elements, only those that were changed to accommodate the new RDD architecture are documented here. Other language elements that are specifically designed for database manipulation and have not been altered (e.g., USE) are documented in the Reference guide.

Chapter 4: DBFCDX Driver Installation and Usage

The DBFCDX database driver provides access to FoxPro 2 (.cdx) and (.idx) file formats. This chapter explains how to install DBFCDX and how to use it in your applications.

Chapter 5: DBFMDX Driver Installation and Usage

The DBFMDX database driver provides access to dBASE IV (.dbf), (.mdx), and (.dbt) file formats. The driver also supports dBASE IV-compatible file and record locking schemes, allowing shared access between Clipper and dBASE IV programs. This chapter explains how to install DBFMDX and how to use it in your applications.

Chapter 6: DBFNDX Driver Installation and Usage

The DBFNDX database driver uses the Clipper driver architecture to access dBASE III PLUS compatible index files within a Clipper program, allowing you to create, access, and update dBASE III and dBASE III PLUS compatible index (.ndx) files. This chapter explains how to install DBFNDX and how to use it in your applications.

Chapter 7: DBFNTX Driver Installation and Usage

DBFNTX is the default database driver for Clipper that lets you create and maintain (.ntx) files with features above and beyond those supplied with previous versions of DBFNTX. This chapter details these new features and explains how to install and use DBFNTX in your applications.

Chapter 8: DBPX Driver Installation and Usage

The DBPX database driver provides access to Paradox 3.5 (.db), (.px), (.x) and (.y) file formats. This chapter explains how to install DBPX and how to use it in your applications.

Chapter 9: Alternate Terminal Drivers

Clipper provides several Alternate Terminal Drivers to allow your applications to run in a wider variety of environments. This chapter discusses how Alternate Terminal Drivers fit into the overall Clipper architecture, as well as how to install and use each of the supplied terminal drivers: ANSITERM, NOVTERM, and PCBIOS.

Format of xBase Files

Posted on by vivaclipper

xBase File Format Description

xBase File Types

Posted on by vivaclipper

xBase File  Types and Extensions

Ext. File Type  Introduced or used by
.$$$ temporary file  dBASE III
.$db temporary file  dBASE IV
.act FoxDoc Action Diagrams  FoxPro
.app application object file  dBASE Appl. Generator
.app generated application  FoxPro
.bak Backup file  dBASE
.bar horizontal bar menu object file  dBASE Appl. Generator
.bin Binary files  dBASE
.bch batch process object file  dBASE Appl. Generator
.cac executable when caching on/off  dBASE IV
.cat catalog  dBASE III, IV
.cdx compound index  FoxPro
.ch header file  Clipper
.cht interface file for ChartMaster  dBASE
.clp compiler script file (clip list)  Clipper
.cmd command  dBASE – Waffle
.cod template source file  dBASE Appl. Generator
.cpt encrypted memo file  dBASE
.crp encrypted database  dBASE IV
.ctl control file  dBASE IV – Aldus Setup
.cvt backup file for CONVERTed database file  dBASE IV
.db configuration  dBASE
.db$ temporary file  dBASE
.db2 database  dBASE II
.db3 database  dBASE III
.dbf database file  dBASE – FoxPro
.dbk database backup  dBASE IV
.dbo compiled program  dBASE IV
.dbt FoxBASE+ style memo  FoxPro
.dbt memo file for database w/same name  dBASE – Clipper
.def Definitions list  dBASE
.dif Data Interchange Format. For APPEND FROM, COPY  dBASE – VisiCal
.doc Documentation text file  dBASE Appl. Generator
.fil files list object file  dBASE Appl. Generator
.fky macro file  FoxPro
.fmo compiled format file  dBASE IV
.fmt format file  dBASE – FoxPro – Clipper
.fp configuration file  FoxPro
.fpc catalog  FoxPro
.fpt memo  FoxPro
.fr3 renamed dBASE III+ form file  dBASE IV
.frg uncompiled report file, code fragment file  dBASE IV
.frm report file  dBASE – Clipper
.fro compiled report file  dBASE IV
.frt report memo  FoxPro
.frx report  FoxPro
.fw2 Framework spreadsheet or database file  Framework – dBASE
.fxp compiled format  FoxPro
.gen compiled template  dBASE Appl. Generator
.idx index (many)  FoxPro
.ind include index  dBASE IV
.inx index  FoxBase
.key Key macro library  dBASE
.lbg label generator data  dBASE IV
.lbl label  dBASE – Clipper
.lbo compiled label  dBASE IV
.lbt label memo  FoxPro
.lbx label  FoxPro
.ld1 overlay file  dBASE
.log Transaction log file  dBASE
.mbk multiple index file backup  dBASE IV
.mdx multiple index file  dBASE IV
.mem memory variable save file  dBASE – FoxPro
.mnt menu memo  FoxPro
.mnx menu  FoxPro
.mpr generated program  FoxPro
.mpx compiled menu program  FoxPro
.ndx index file  dBASE
.npi source for DGEN.EXE interpreter  dBASE Appl. Generator
.ntx index file  Clipper
.pjt project memo  FoxPro
.pjx project  FoxPro
.plb library  FoxPro
.pll pre-linked library  Clipper
.plt pre-linked transfer file  Clipper
.pop pop-up menu object  dBASE Appl. Generator
.ppo pre-processor output  Clipper
.pr2 printer driver  dBASE IV
.pr3 PostScript printer driver  dBASE IV
.prf printer driver  dBASE IV
.prg program source file  dBASE – FoxPro – Clipper
.prs procedure  dBASE IV
.prt Print dump  dBASE
.prx compiled program  FoxPro
.qbe saved query (Query By Example)  dBASE IV – Quattro Pro
.qbo compiled query  dBASE IV
.qpr generated query program  FoxPro
.qpx compiled query program  FoxPro
.qry query  dBASE IV
.res dBASE resources  dBASE IV
.rpd Rapid file. For IMPORT/EXPORT,APPEND  FROM, COPY  dBASE
.sc3 renamed dBASE III screen mask file  dBASE IV
.scr screen – screen snapshot  dBASE IV
.sct screen memo  FoxPro
.scx screen  FoxPro
.spr generated screen program  FoxPro
.spx compiled screen program  FoxPro
.str structure list object file  dBASE Appl. Generator
.t44 Temporary file for Sort or Index  dBASE IV
.tbk memo backup  dBASE IV – FoxPro
.tvf table view settings  dBASE
.upd update data  dBASE
.upo compiled update data  dBASE
.val values list object file  dBASE Appl. Generator
.vew view file  Clipper, Lotus Approach
.vue view  dBASE IV – FoxPro
.w44 temporary file for Sort or Index  dBASE
.wfm form object  dBASE Form Designer
.win window file  FoxPro – dBASE

Source :  http://www.clicketyclick.dk/databases/xbase/format/index.html

Notes:

–          Such a list can’t be perfect. Some item may be obsolete / forgotten and something may not exist when this list compiled.

–          “Clipper” may not include all versions of Clipper.

–          Most of Clipper files are supported by Harbour.

Identifier length limit

Posted on by vivaclipper

What is variable and field name length limit in Harbour ?

Harbour support long field names without any problem.

TBrowse in Harbour also does not have any 10 character limit.

Variable and field names in Harbour can have up to 63 characters. This limit is defined in hbvmpub.h:

#define HB_SYMBOL_NAME_LEN 63

and can be changed to any bigger value if necessary.

All problems are result of DBASE III DBF format which has 10 character field name limit.

It’s not Harbour problem but DBF structure created many years ago which cannot be changed due to compatibility with other systems using such files.

If you want to use longer field names then you have to chose RDD which uses different low level storage format then DBASE III DBF and supports longer field names.

Przemek

(Source)

Tom Rettig

Posted on by vivaclipper 


Tom Rettig was a major guru in the dBASE, Clipper and whole xBase community.  Among Tom’s accomplishments multiple utilities that allowed development in xBase to be easier and faster.


Tom Rettig was one of the main reasons we can use the term “community” when we talk about the groups of xBase people. Tom was one of the designers of dBASE III and wrote the essential reference book on it. He built the first add-on library for Clipper, pioneering the public domain tools that make xBase jobs easier. Tom wrote articles for many xBase magazines and periodicals. Tom Rettig’s Help and Tom Rettig’s Handbooks taught us the some complexity and difficulty of xBase.


He participated in the IEEE xBASE “standardization” efforts. Tom is considered one of main gurus of xBase history. His program and documentations are legendary.


 


A “Program for Life” authored by the late Tom Rettig










* remember.prg
* Sometimes we forget...






USE Yourself exclusive

SET TALK OFF
CLEAR

DO WHILE ALIVE
   STORE "LOVE" TO heart
   STORE "health" TO body
   STORE "peace" TO mind
   STORE "compassion" TO others
   STORE "esteem" TO self
   STORE "faith" TO God

   REPLACE Negative   WITH Positive , ;
           Judgment   WITH Acceptance , ;
           Resentment WITH Forgiveness

   REPLACE Hopelessness    WITH Choice , ;
           Confusion       WITH Clarity , ;
           Procrastination WITH Participation

   REPLACE Separation WITH Connection , ;
           Lack       WITH Abundance , ;
           Sorrow     WITH Celebration

   @ all, times SAY your_truth

   If its_time
      EXIT
   ENDIF

ENDDO

SAVE TO Always
CLEAR ALL

RETURN

* EOF: remember.prg

















			

	
	



		
			


	

		
Mere Clipper


		

		Posted on  by vivaclipper		

	


		

		
An article by Roger Donnay, March, 1998


.


We often do not realize the importance of people and events until many years later when the dust has settled and we can put them into perspective. Three years ago I was asked to write an article for the CDGN Magazine. It was titled “Back to the Future” and it dealt with the the role of Clipper in 1995 and into the future. I recently broke out my old copy of CDGN magazine and reread the article to see if my predictions match the current landscape.


.


I predicted that I would be writing my final article about Clipper in the year 2035. Many of you assumed that either I was much younger than I really am, that this was a typographical error, or that I had already lost it and was living on a ranch somewhere in California with Ronald Reagan. None of the above are true. I am now fifty-four years old. In the year 2035, I will be 91 years old but I will still be programming because in the year 2007 we will discover a new drug that restores dead brain cells. The year 2035 will mark the year that we finally arise from the ashes of the “great computer meltdown” of 2010. The meltdown will occur because of the Year 2000 debacle which will create a world-wide depression and create a political climate of hatred towards programmers that will build to a frenzy leading to “The Night of Broken Disks”. Computer programmers will be fleeing to Russia, Iran and Iraq – the only safe havens in the world that will not be affected by the “Great-Satan Virus” due to their refusal to connect to the Information SuperHighway.


.


This great oppression of computer programmers will force those who are not killed outright, or sent to “de-programming camps” made their escape to third-world countries to hide for years in attics, befriended by a few, brave souls who know it is not their fault they were born “computer-literate”. During this 20-year war on computers, an arsenal of “giant magnets” are created by the new war machine and the industrialized cities of the world are bombed with the largest “de-gaussing” campaign in history. No piece of software or database will be safe from annilation. Finally, the great war machine is defeated because it will fail to realize that it cannot maintain such a war when it destroys the very machines and software that allow it to wage war.When it is all over, a discovery is made in a little house on the Prinsengracht in Amsterdam. A old notebook computer is found in the attic and sent to a museum. While restoring the computer, a small disk is found, still fused in the disk drive. Because of its condition, it appears that the notebook had been there for many years. Much work goes into the restoration of the disk and its data and finally, it is discovered that the disk contains the diary of a young, computer-literate girl who had lived in hiding for many years. By this time, the only computer-literate people left in the world only speak Russian or Farsi, so it takes much effort to figure out how to decipher the data on the disk. Finally, a compelling and sad story emerges about a young girl who struggles to maintain her innocence, her sanity, her computer-proficiency, and her faith in God while hiding from the great de-gaussing and de-programming regime.


.




It is a sad story, and it takes time for the world to really understand her story, especially her references to “The Book of Clipper”. What was Clipper? Was this what helped her maintain her sanity and her faith in God? What happened to the young girl? Her story spreads around the world, and a never-ending search continues for a copy of “The Book of Clipper”. Finally, the search ends in a little Russian town. Not a single person realizes that “The Book of Clipper” is a reference to the manual for the computer language that every single Russian speaks fluently, until someone finds a copy of the manual that Larry Heimendinger had left at the only Russian Clipper conference ever held – in 1992. It is dusty and worn, but it is the only book left that tells the true story of Clipper. Even though every programmer in Russia can speak Clipper, not a single one of them has seen a copy of “The Book of Clipper” because none had ever been sold. The software had been pirated, and then spread from disk to disk throughout the country while the story of Clipper passed from mouth to mouth. The Russians are the only civilized society that still has a programming language, so they offer it as a gift to the world, and the world becomes whole again, and the people rejoyce, and I come out of hiding – to write my final article about Clipper.


It’s a Wonderful Life


I like to imagine that I am the angel in the story “It’s a Wonderful Life” and that I have been called on by God to rescue a person who feels that his life has been lived in vain. In my rendition of the story, the desperate soul is not George Bailey but instead is Tom Rettig. Tom passed away about a year ago and I find myself haunted by him because I feel that I have never given back to him what he gave to me and the rest of the world. I often think back at what my life was like in the mid 80’s. After many successful years as an Electronics Engineer my life was just not working anymore. Thieves broke into my business office and stole my computers and my software (including the backups). I was struggling with a failing computer-accessories manufacturing business that had pushed me deep into debt, and then my wife decided to just leave one day and head for greener pastures. I thought she had been kidnapped because she disappeared without a trace.


Arlo Guthrie once wrote a song about “The Last Man”. He said “You think you’ve got it bad? Look at that guy?.” I WAS that guy.


Then, one day, in early 1986 I was struggling with a problem trying to get dBase-III to work properly on my new peer-to-peer network. I recall making a tech support call to the network developer and the person on the phone asked “Are you compiling with Clipper?”


This simple question, in retrospect, was equivalent to someone posting a huge sign “Except a man be born again, he cannot see the kingdom of God”. Clipper was my salvation. It allowed me to layeth down in green pastures and it restoreth my soul. So how did it come about that a person could be saved from the depths of depravity by a mere software product? We all have our stories of salvation, and they all take us down different paths but they all lead to the same place. My story in not unlike C.S. Lewis’ story in “Mere Christianity”, except the players are different. The Book of Clipper is not one story, but hundreds of stories all evolving from the “Platitudes of Vulcan”.


Tom Rettig entered the scene around 1986 and offered an add-on product to Clipper titled “Tom Rettig’s Library”. Tom was a well-liked, generous person who eventually offered his library into the public-domain. Some of us are old enough to remember him as Jeff, the small boy in the original “Lassie” series on television in the 50’s. I first met him at a user group in Southern California. After the meeting we went to a bar for a few beers and he sat and talked to us like we had all known him for years. He inspired us to do what he did, because he was just like us. The next day, I thought “If Tom Rettig can make a successful add-on product to Clipper, so can I”. I wasn’t the only person who had seen the light that night. Tom had broken new ground, had planted the first seeds, and from these seeds, an entire community of user-groups, programmers, applications, add-on products, books, magazines, et al, grew into maturity.


Two Steps Back


Have you ever heard anyone say “He’s so far behind he’s ahead”? By now, most of you have decided that you must move on to Windows and that there is no place for Clipper in your strategy. Many of you have already done so and are experimenting with products like VO, Delphi, VB, and Power-Builder or have created applications with these development environments. I am not writing this article to suggest that in any way, this was a bad choice. I have spent sufficient time with these products to come to the realization that Windows applications can be developed by travelling many different paths. What I am offering, however, is another perspective; one that frees us to open our minds to look at the future from a different view. Many of us have been so busy and so worried about constantly moving forward that we have forgotten how we got here in the first place, by the use of an enduring and powerful language – Clipper.


So you may be thinking “What is he talking about? Clipper is Dead!”. In the sense of a product, this may be true, but in the sense of a language, it is far from true. Let’s imagine that Chinese is packaged into a product named “Visual-Chinese” and this product includes a set of design-tools for creating quick-Chinese documents that can be easily integrated into our marketing documents. Soon we would find our business opened up to a new market of 1 billion people. The product becomes instantly successful and everyone love its and uses it – until, years later, when we find that our marketing documents are not delivering any sales. Why? Because the language had to be cut and trimmed to fit into the limitations of the software environment. It becomes ambiguous, arrogant and unwanted by the very people who inspired its development, so it dies and Visual-Chinese gets thrown away like every other Visual tool. Does this mean that the Chinese language dies with the product? No. Chinese is a language that will endure. It has lots of users; it is robust, and it is mature.


The key word is “language“. Development strategies should be built around the choice of a proper language, not just a product. Clipper is a language that endures. It cannot die. It has widespread use around the world and there are hundreds of thousands of Clipper legacy applications still doing mission- critical work. Unfortunately, because the word “Clipper” is owned by CA, and because CA has essentially abandoned Clipper, it cannot endure under the name Clipper, so it must endure under another name: that name is “Xbase”. Software developers try to treat languages like they own them, but they are only temporary custodians. This leads us to a discussion of the current state of the Xbase language. Xbase currently ( 1998 ) exists in 5 dialects:


    

      1. dBase – A Windows-based Interpreter.
    



    

      2. FoxPro – A Windows-based Interpreter.
    



    

      3. CA-Clipper – A DOS-based Xbase compiler.
    



    

      4. CA-VO – A 32-bit Windows-based Xbase compiler.
    



    

      5. Xbase++ – A 32-bit Multi-Platform Compiler.
    



Xbase as dBase


dBase was the custodian of the Xbase language from around 1983 until about 1987. Unfortunately, it was an interpretive language so it never gained respectability as a true, robust language, however, it had much to offer the developer in ease-of-use and database design. dBase continues to be supported by Borland, simply because there is still money to be made in upgrades and conferences, but Borland has made it clear that they intend to make dBase programmers learn how to speak Pascal and eventually will phase Xbase out of their products.


Xbase as FoxPro


FoxPro took over as a co-custodian of the Xbase language in about 1987 and emerged around the same time as Clipper. FoxPro defeated dBase nearly overnight simply because it was faster, not because it delivered any new language concepts. FoxPro continues to be supported by Microsoft, simply because there is still money to be made in upgrades and conferences, but Microsoft has made it clear that they intend to make FoxPro programmers learn how to speak Visual Basic and eventually will phase Xbase out of their products.


Xbase as Clipper


Clipper was undoubtely the best custodian of the Xbase language from 1987 to 1996. Clipper introduced the Xbase compiler, the open-architecture concept of the extend system, code blocks, locals, statics, multi-dimensional arrays, the RDD layer, the preprocessor, and language extensions. Clipper was the first Xbase custodian to give Xbase respectability as a true programming language. Clipper maintained this respectability until around 1996 when CA released CA-Clipper 5.3. CA chose to treat Clipper as a “package” rather than a “language” and alienated nearly the entire Clipper community when they bundled a Windows-IDE and several third-party products into the package. This was when Clipper died.


Xbase as VO


Computer Associates planned for VO to take over as the custodian of the Xbase language by forcing the death of Clipper and dragging CA customers into a new kind of development environment that kind of looks like Clipper, in that it inherited much of the new Clipper extensions. Unfortunately, migration to VO became cumbersome due to too many incompatabilities, poor performance, poor reliability and a third-party community who could not get their products to work with VO. VO promised it would be easy to migrate existing Clipper applications to Windows but could not deliver on the promise. Working in VO is in no way similar to working in Clipper. Many Clipper developers find that using a third-party Windows library (like Five-Win or Clip-4-Win) with Clipper is a much easier migration path than VO.


…


Why Xbase?


Many of us wonder why Xbase has not been given more respectability as a “mainstream” language. If Xbase is so good, why are Borland and Microsoft phasing it out of their future products? I was watching a television program the other day about an analysis of automobile technology over the years. We often assume that the best technology is what endures over time and that it eventually rises to the top. This may be true in an ideal world, but in a capitalist society, it is usually market dog-fights that determine dominance. In this analysis, it was determined that steam technology could have produced cars just as good as internal combustion technology, but Henry Ford chose the latter. Bill Gates has chosen Basic, not because it is better, but because he owns it. He doesn’t own Xbase, and Bill cannot embrace something that he cannot control. Borland chose Pascal. Not because it is better, but becaused they own it.


Over the past 10 years, the success of the Xbase products has been due to the high degree of abstraction of the Xbase language, which makes it vastly simpler to acces and use operating system functions and resources. In addition, Xbase is more than just a specialized programming language, a database navigation language, or a user interface language – instead, it combines all of these roles, harmoniously integrating them with one another.


Xbase offers dynamic data types and is generally described as being highly “tolerant“. Taken together, these benefits have persuaded a steadily growing community of users and developers to rely upon it as a choice for implementing mission-critical and commercial PC-desktop applications. In fact, world-wide, more than one-third of all DOS-based commercial applications now in use were written in Xbase, with Clipper accounting for the major share.


…


Square Pegs and Round Holes


Most Windows programmers will tell you that you cannot take a standard Clipper application with @SAY..GETS, Menu Prompts, etc, and convert it to a Windows GUI program without a major change in the architecture and the functionality of the program. They claim that a text-based, modal design has too little in common with GUI-based, event-driven, non-modal design. They will tell you that it like trying to fit a square peg into a round hole. For years, I believed this because it made sense. I, like everyone else, wrote my Windows applications with a different structure than my Clipper applications. They were built around an event model rather than a procedural model and the code was tightly-bound rather than loosely-bound to the functional model. This always leaves me with an uneasy feeling because it forces me to write applications that are less modular and are platform specific. Microsoft, Borland, and CA each wants us to build applications their way. They want us to learn their programming tools, their methods, their plug-ins, their workshops, and their studios – not their language. Why? Because applications built around their environment will be harder to migrate to competitor’s products than applications built around a language.


So they make sure that the language is difficult and inaccessible, and that the application cannot be maintained or migrated to any other platform, other than platforms that they support. Programmers, however, have to survive in the real world and this requires platform flexibility. The reason why so many mission- critical DOS applications are still surviving in the real world is because each development platform supports DOS as a subset, so DOS has been, out of necessity, elevated to the status “platform independent”. I can run my Clipper applications under MS-DOS, PC-DOS, DR-DOS, OS/2, Windows 3.1, Windows 95, Citrix- Winframe, MULTI-DOS, Windows NT and Novell-DOS. I can run my Delphi applications only under 32-bit Windows. Is this a step forward?


…


Cocoon


In my dream, the “Ghost of Xbase Future” led me through the Land of Clipper and how it might look like up through the year 2035. I couldn’t hold back my emotions as I witnessed the data meltdown and the termination of millions of programmers. I asked him “Spirit – is this a vision of how things MUST be or how things COULD be?” He never answered me. I woke up from my dream and ran to the mirror. I was relieved to see that I wasn’t 91 years old but was still a young man. I exclaimed “There’s still time!” I bolted to the window, looked out, and saw that The Land of Clipper looks different than it did yesterday. The paths are 32-bits wide and they lead everywhere, yet they look familiar and something tells me that there is nothing to fear at the end of these paths. Then I realized that I had not been dreaming and that Clipper had not really died at all but had been in a cocoon, waiting to metomorphose into a butterfly, one with big X’s on it’s wings. The butterfly is beautiful and it attracts the attention of people like Dirk Lesko (author of Funcky), of Jud Cole (author of Blinker), of Dave Kuechler (author of Comix), and others who once frolicked in the land of Clipper.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Note: This article is a summary  ( by courtesy of author) original is here.



			

	
	



		
			


	

		
What is Clipper ?


		

		Posted on  by vivaclipper		

	


		

		
As a computer software term, the word “Clipper” has two meaning :


1- A programming language


2- A compiler


As a computer programming language that is used to build software programs that originally operated primarily under DOS. Although it is a powerful general-purpose programming language, it was primarily used to construct  database/business programs.


Clipper was originally released in 1985 as a compiler for dBASE III, a very popular database language at the time. Compiling dBASE code changes it from interpreted code, which must be interpreted every time each line of code is executed, to p-code, which uses a Virtual Machine to process the compiled p-code. p-code is considerably faster, but still not as fast as the machine code generated by native compilers. As a technical marketing ploy, the p-code was wrapped into object code (linkable .obj files) which gave the impression that it was compiled to native code. Clipper was created by Nantucket Corporation led by Barry ReBell (political) and Brian Russell (technical), and later sold to Computer Associates. GrafX Software licensed CA-Clipper in 2002 from CA for ongoing marketing and distribution.


As the product matured, it remained a DOS tool for many years, but added elements of the C programming language and Pascal programming language, as well as OOP, and the code-block data-type (hybridizing the concepts of dBase macros, or string-evaluation, and function pointers), to become far more powerful than the original. Nantucket’s Aspen project later matured into the Windows native-code Visual Objects compiler.


After “swallow” Nantucket at 1992, CA published a few releases of Clipper Compiler, lastly 5.3a at  May 20, 1997. But most of Clipper programmer uses preferably 5.2e – released February 7, 1995.


Although remained a DOS as the compiler, Clipper continues to live as the programming language.


The Clipper language is being actively implemented and extended by multiple organizations/vendors, like xBase ++ from Alaska Software and FlagShip, as well as free(GPL-licensed) projects like Harbour and xHarbour.


Many of the current implementations are portable (DOS, Windows, Linux (32- and 64-bit), Unix (32- and 64-bit), and Mac OS X), supporting many language extensions[1], and have greatly extended runtime libraries, as well as various Replaceable Database Drivers (RDD) supporting many popular database formats, like DBF, DBTNTX, DBFCDX (FoxPro, Apollo and Comix), MachSix (SIx Driver and Apollo), SQL, and more. These newer implementations all strive for full compatibility with the standard dBase/xBase syntax, while also offering OOP approaches and target-based syntax such as SQLExecute().


Version history


The various versions of Clipper compiler were:


From Nantucket Corporation; the “seasonal versions”, billed as “dBase compilers”


    

  • Nantucket Clipper Winter’84 – released May 25, 1985
    • 

  • Nantucket Clipper Summer’85 – released 1985
    • 

  • Nantucket Clipper Winter’85 – released January 29, 1986
    • 

  • Nantucket Clipper Autumn’86 – released October 31, 1986
    • 

  • Nantucket Clipper Summer’87 – released December 21, 1987
    • 



From Nantucket Corporation; Clipper 5


    

  • Nantucket Clipper 5.00 – released 1990
    • 

  • Nantucket Clipper 5.01 – released April 15, 1991
    • 

  • Nantucket Clipper 5.01 Rev.129 – released March 31, 1992
    • 



and from Computer Associates; CA-Clipper 5


    

  • CA Clipper 5.01a –
    • 

  • CA Clipper 5.20 – released February 15, 1993
    • 

  • CA-Clipper 5.2a – released March 15, 1993
    • 

  • CA Clipper 5.2b – released June 25, 1993
    • 

  • CA-Clipper 5.2c – released August 6, 1993
    • 

  • CA Clipper 5.2d – released March 25, 1994
    • 

  • CA-Clipper 5.2e – released February 7, 1995
    • 

  • CA Clipper 5.30 – released June 26, 1995
    • 

  • CA Clipper 5.3a – released May 20, 1996
    • 

  • CA Clipper 5.3b – released May 20, 1997
    • 



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Note: This post is based upon mainly a Wikipedia article :


http://en.wikipedia.org/wiki/Clipper_(programming_language)