Tag Archives: Abbreviation

Coding Guidelines

Posted on by vivaclipper

Coding Guidelines

( by Greg Holmes )

Language Syntax 
The general rule of thumb is: built-in features in lowercase, and custom-written functions in mixed case. 
When specifying the complete syntax of a language element in documentation, the input items, parameters, and so on are referred to using the following symbols:

 Symbol  Description
< >  Indicates user input item
( )  Indicates function argument list
[ ]  Indicates optional item or list
{ }  Indicates code block or literal array
| |  Indicates code block argument list
–>  Indicates function return value
…  Repeated elements if followed by a symbol
Intervening code if followed by a keyword
,  Item list separator
|  Indicates two or more mutually exclusive options
@  Indicates that an item must be passed by reference
*  Indicates a compatibility command or function

For example:

    len(<cString>|<aArray>) --> nLength

Metasymbols provide a place holder for syntax elements, and they describe the expected data types. A metasymbol consists of one or more lowercase data type designators followed by a mixed case description. This is known as Hungarian Notation.

 Designator  Description
a  Array
b  Code block
c  Character expression
d  Date expression
exp  Expression of any type
id  Literal identifier
l  Logical expression
m  Memo field
n  Numeric expression
o  Object
x  Extended expression

In this example, dnLower and dnUpper can be either date or numeric:

    @...get...range <dnLower>, <dnUpper>
Filenames and Aliases 
All filenames, in any context, are in upper case. Filenames follow DOS naming conventions (preferably limited to letters, numbers, and the underscore).

    use CUSTOMER
    nHandle := fopen('DATAFILE.DAT')

When referring to specific file types in documentation, include the period.
e.g. “A program is stored in a text file with a .PRG extension.” 
Alias names follow the same conventions as filenames, but are limited to A-Z, 0-9, and the underscore. If a filename begins with a number or contains unusual characters, an alias must be specified when the file is opened or an error will result. 
Note that CA-Clipper does not natively support Windows 95 long filenames, although third-party libraries are available to add the capability.
Fieldnames 
Fieldnames are all uppercase, and always include the alias of the table. Fieldnames may contain underscores, but should not begin with one (because the underscore is generally used to indicate an internal symbol).

    @ 10, 10 say BANKS->BRANCH
    nAge := CUSTOMER->CUST_AGE
Memory Variables 
Memory variables consist of a lowercase type designator followed by a mixed case description (see Hungarian Notation). Although CA-Clipper only recognizes the first 10 characters as unique, variable names may be longer.

    cString := "Hello World"
    nYearlyAverage := CalcYearAvg()

If you use Hungarian Notation for your memory variable names and include the table alias with fieldnames, there will be no conflict between the two.
Commands, Functions, and Keywords 
All built-in commands, functions, and keywords are lowercase. In documentation, the font should be Courier or a similar font. If fonts are not available, then bold or CAPITALIZE the word for emphasis. 
Never use abbreviations — this practice is not necessary with a compiler, although it was common in the early days of dBase (which was an interpreter). 
There should never be a space between the function name and the opening parenthesis. Also, note that the iif() function should never be spelled if().

    replace CUSTOMER->CUSTNAME with cCustName
    nKey := inkey(0)

When specifying commands that have clauses in documentation, separate the keywords with an ellipsis (...) and do not include the to clause, unless it is followed by the file,print, or screen keywords.

    copy...sdf
    set message...center
    @...say...get
Programmer-Defined Functions & Procedures 
These begin with an uppercase letter, followed by mixed case letters as appropriate.

    ? StripBlanks("Hello there, this will have no spaces.")

Function and procedure names may contain underscores, but should not begin with one (they may conflict with internal functions which often start with an underscore). There should be only one return statement per function or procedure, and it should not be indented.

    function SomeFunc (...)
      .
      . <statements>
      .
    return cResult

The return value of a function is not enclosed in parentheses, although parentheses may be used to clarify a complex expression.

    return nValue
    return (nCode * 47) + nAnswer
Preprocessor Directives 
Preprocessor directives are lowercase and are preceded by the # sign.

    #include 'INKEY.CH'

Optionally, you may use single quotes around header files that come with CA-Clipper and double quotes around your own. This convention is purely voluntary, but it helps to distinguish between the two. For example:

    #include 'INKEY.CH'
    #include "MY_APP.CH"

Manifest constants are uppercase.

    #define ESCAPE   27
    if lastkey() == ESCAPE

Pseudo-function names should also be uppercase.

    #define AREA(length, width)   ((length)*(width))
Declarations 
Local variables are grouped according to functionality, and may be declared on one or more lines. The declarations appear as the first code at the beginning of a function or procedure.

    procedure Main ( )
    local nTop, nLeft, nBottom, nRight
    local cOldScreen, cOldColor, nOldCursor

Variables may be declared one per line and accompanied by a description.

    local nCount        // Number of records found.
    local nTotal        // Sum of dollars.

The description can be omitted if better variable names are chosen.

    local nRecordCount
    local nDollarTotal

Variables can be initialized when they are declared, although it is often clearer (and safer) to initialize them immediately before they are used.

    local nRecordCount:=0
    local nDollarTotal:=0
Logicals 
The .T. and .F. are typed in uppercase.
Operators 
The in-line assignment operator (:=) is used for all assignments, and the exact comparison operator (==) is used for all comparisons.

    lContinue := .T.
    nOfficeTotal := nRegionTotal := 0
    lDuplicate := (CUSTFILE->CUSTNAME == cCustName)
    if nLineCount == 4  ...
    if left(PRODUCT->CODE, 3) == left(cProdCode, 3)  ...

Although the compound assignment operators (+=, -=, *=, etc.) are convenient, they should not be used if readability suffers.

    // The traditional way to accumulate:
    nTotal := nTotal + INVDETAIL->PRICE
    // A good use of a compound assignment operator:
    nTotal += INVDETAIL->PRICE
    // But what does this do?
    nVal **= 2

The increment (++) and decrement (--) operators are convenient, but can lead to obscure code because of the difference between prefix and postfix usage.

    nRecCount++
    nY := nX-- - --nX        // Huh?
Spacing 
Whenever a list of two or more items is separated by commas, the commas are followed by a space.

    MyFunc(nChoice, 10, 20, .T.)

Spaces may be used between successive parentheses.

    DoCalc( (nItem > nTotal), .F. )
    cNewStr := iif( empty(cStr), cNewStr, cStr + chr(13) )

Spaces should surround all operators for readability.

    nValue := 14 + 5 - (6 / 4)

In declarations, often spaces are not used around the assignment operator. This tends to make searching for the declaration of a variable easier.

    local lResult:=.F., nX:=0

Thus, searching for “nX :=” would find the lines where an assignment is made, while searching for “nX:=” would find the declaration line (such as the local above).
Indentation 
Indenting control structures is one of the easiest techniques, yet it improves the readability the most. 
Indent control structures and the code within functions and procedures 3 spaces.

    procedure SaySomething
       do while .T.
          if nTotal < 50
             ? "Less than 50."
          elseif nTotal > 50
             ? "Greater than 50."
          else
             ? "Equal to 50."
          endif
          ...
       enddo
    return

Case statements in a do…case structure are also indented 3 spaces.

    do case
       case nChoice == 1
          ? "Choice is 1"
       case ...
          ...
       otherwise
          ...
    endcase
Tabs 
Do not use tabs in source code — insert spaces instead. Tabs cause problems when printing or when moving from one editor to another, because of the lack of a standard tab width between editors and printers. Typically, printers expand tabs to 8 spaces which easily causes nested control structures to fall off the right-hand side of the page. Commonly, a source code editing program will insert the appropriate number of spaces when the <TAB> key is hit.
Line Continuation 
When a line of code approaches the 80th column, interrupt the code at an appropriate spot with a semicolon and continue on the next line. Indent the line so that it lines up in a readable manner.

    set filter to CUSTFILE->NAME  == 'John Smith  ';
            .and. CUSTFILE->STATE == 'OR'

To continue a character string, end the first line with a quote and a plus sign and place the remainder on the next line. Try to choose a logical place in the string to break it, either at a punctuation mark or after a space.

    @ 10, 10 say "The lazy brown fox tripped over " + ;
                 "the broken branch."
Quotes 
Use double quotes for text that needs to be translated (will appear on the screen), and single quotes for other strings.

    ? "Hello World!"
    cColor := 'W+/B'
    SelectArea('PROP')

This is a simple but extremely effective technique because translation departments often want to see the messages in context (in the source code), so the different quote types indicate which messages are to be translated and which should be left alone.
Comments 
Comments are structured just like English sentences, with a capital letter at the beginning and a period at the end.

    // Just like a sentence.
    /* This comment is longer. As you
       can see, it takes up two lines */

You may encounter old-style comment indicators if you maintain older (Summer’87 and earlier) code.

    && This is an older-style of comment indicator.
    *  The asterisk is also old.

For in-line comments, use the double slashes.

    use CUSTOMER            // Open the data file.
    goto bottom             // The last record.

Note that the ‘//‘ of in-line comments begins at column 40, if possible. This leaves enough room for a useful comment.

Source :  http://www.ghservices.com/gregh/clipper/guide.htm

Pre-processor Terms

Posted on by vivaclipper

Abbreviation :

A source token whose leftmost characters exactly match the leftmost characters of a keyword in a translation directive. Abbreviations must be at least four characters in length.

Blockify :

To change an expression in the source text into a code block definition. Blockifying is accomplished by surrounding the source text with braces and placing an empty block parameter list (a pair of vertical bars) just inside the braces. When the resulting code block is evaluated at runtime, the original expression will be evaluated.

Blockify Result Marker :

A result marker of the form <{id}>. id must correspond to the name of a match marker. A blockify result marker specifies that the corresponding source text is to be blockified. If the matched source text is a list of expressions, each expression in the list is individually blockified. If no source text matched the corresponding match marker, an empty result is produced.

Conditional Compilation :

Selective exclusion by the preprocessor of certain source code. The affected source code is bracketed by the #ifdef and #endif directives. It is excluded if the argument in the #ifdef directive is not a #defined identifier.

Define :

To #define an identifier to the preprocessor and optionally specify text to be substituted for occurrences of the identifier.

Directive :

An instruction to the preprocessor. Preprocessor directives must appear on a separate line, and must begin with a hash mark (#). Their scope or effect extends from the point where they are encountered to the end of the source file in which they appear.

Dumb Stringify Result Marker :

A result marker of the form #<{id}>. id must correspond to the name of a match marker. A dumb stringify result marker specifies that the corresponding source text is to be enclosed in quotes. If the matched source text constitutes a list of expressions, each expression in the list is individually stringified. If no source text was matched, an empty pair of quotes is produced.

Empty Result :

An absence of result text; the effect of certain result markers when the corresponding match marker did not match any source text (but when the translation directive as a whole was matched). An empty result simply implies that no result text is written to output.

Header File :

A source file containing manifest constant definitions; command or pseudofunctions; and/or program statements merged into another source file using the #include preprocessor directive.

Identifier :

A name that identifies a function, procedure, variable, constant or other named entity in a source program. In Clipper language, identifiers must begin with an alphabetic character and may contain alphabetic characters, numeric characters, and the underscore character.

Include File :

A source file included another source file via #include directive. Though it is a header file by convention, pratically may be any source file.

See : Header File, source file

List Match Marker :

A match marker indicating a position that will successfully match a list of one or more arbitrarily complex expressions. A list match marker marks a part of a command that is expected to consist of a list of programmer-supplied expressions. A list match marker has the form <id,…>. id associates a name with the match marker. The name can be used in a result marker to specify how the matching source text is to be handled.

Logify :

To change an expression in the source text into a logical value. Logifying is accomplished by surrounding the expression with periods.

Logify Result Marker :

A result marker of the form #<.id.>. id must correspond to the name of a match marker. This result marker writes true (.T.) to the result text if any input text is matched; otherwise, it writes false (.F.) to the result text. The input text itself is not written to the result text.

Manifest Constant :

An identifier specified in a #define directive. The preprocessor substitutes the specified result text whenever it encounters the identifier in the source text.

Match :

A successful comparison of source text with a match pattern (or part of a match pattern).

Match Marker :

A construct used in a match pattern to indicate a position that will successfully match a particular type of source text. There are several types of match markers, each of which will successfully match a particular type of source text.

Match Pattern :

The part of a translation directive that specifies the format of source text to be affected by the directive. A match pattern generally consists of words and match markers.

Normal Stringify Result Marker :

A result marker of the form <“id”>. id must correspond to the name of a match marker. A normal stringify result marker specifies that the corresponding source text is to be enclosed in quotes. If the matched source text is a list, each element of the list is individually stringified. If no source text was matched, an empty result is produced.

Optional Clause :

A portion of a match pattern that is enclosed in square ([ ]) brackets. An optional clause specifies part of a match pattern that need not be present for source text to match the pattern. An optional clause may contain any of the components legal within a match pattern, including other optional clauses. When a match pattern contains a series of optional clauses that are immediately adjacent to each other, the matching portions of the source text are not required to appear in the same order as the clauses in the match pattern. If an optional clause is matched by more than one part of the source text, the multiple matches may be handled using a repeating clause in the result pattern.

Preprocessor :

A translation program that prepares source code for compilation by applying selective text replacements. The replacements to be made are specified by directives in the source file. In Clipper language, the preprocessor operates transparently as a part of the compiler program.

See Also : Compiler

Pseudofunction :

A function-like construct that is replaced with another expression via the #define directive, rather than compiled into a conventional function call. Pseudofunctions may contain parenthesized arguments that may be included in the substituted text.

Regular Match Marker :

A match marker indicating a position that will successfully match an arbitrarily complex expression in the source text. A regular match marker generally marks a part of a command that is expected to consist of arbitrary programmer-supplied text, as opposed to a keyword or other restrictive component. In order for the source text to match, it must constitute a properly formed expression. A regular match marker has the form <id>. id associates a name with the match marker. The name can be used in a result marker to specify how the matching source text is to be handled.

Regular Result Marker :

A result marker of the form <id>. id must correspond to the name of a match marker. This result marker writes the matched input text to the result text, or nothing if no input text is matched.

Repeating Clause :

A portion of a result pattern surrounded by square ([ ]) brackets. The text specified by the repeating clause is written to output once for each successfully matched match marker in the corresponding match pattern.

Restricted Match Marker :

A match marker indicating a position that will successfully match one or more specified keywords. A restricted match marker marks a part of a command that is expected to be a keyword. A restricted match marker has the form <id: wordList> where wordList is a list of one or more keywords. Source text is successfully matched only if it matches one of the keywords (or is an acceptable abbreviation). id associates a name with the match marker. The name can be used in a result marker to specify how the matching source text is to be handled.

Result Text :

The text that results from formatting matched source text using a result pattern. If the result text matches a match pattern in another preprocessor directive, then it becomes the source text for that directive. Otherwise, the result text is passed as input to the compiler.

Result Pattern :

The part of a translation directive that specifies the text to be substituted for source text that matches the match pattern. A result pattern generally consists of operators and result markers.

Smart Stringify Result Marker :

A result marker of the form <(id)>. id must correspond to the name of a match marker. A smart stringify result marker specifies that the corresponding source text is to be enclosed in quotes unless the source text was enclosed in parentheses. If the matched source text is a list, each element of the list is individually processed. If no source text was matched, an empty result is produced. The smart stringify result marker is used to implement commands that allow extended expressions (a part of a command that may be either an unquoted literal or a character expression).

Source Text :

Text from a source file, processed by the preprocessor. Source text is examined to see if it matches a previously specified match pattern. If so, the corresponding result pattern is substituted for the matching source text

STD.CH :

The standard header file containing definitions for all Clipper language commands.

Stringify :

To change source text into a literal character string by surrounding the text with quotes.

Text Replacement :

The process of removing portions of input text and substituting different text in its place.

Token :

An elemental sequence of characters having a collective meaning. The preprocessor groups characters into tokens as it reads the input text stream. Tokens include identifiers, keywords, constants, and operators. White space, and certain special characters, serve to mark the end of a token to the preprocessor.

Translation Directive :

A preprocessor instruction containing a translation rule. The two translation directives are #command and #translate.

Translation Rule :

The portion of a translation directive containing a match pattern followed by the special symbol (=>) followed by a result pattern.

Undefine :

To remove an identifier from the preprocessor’s list of defined identifiers via the #undefine directive.

Wild Match Marker :

A match marker indicating a position that will successfully match any source text. A wild match marker matches all source text from the current position to the end of the source line. A wild match marker has the form <*id*>. id associates a name with the match marker. The name can be used in a result marker to specify how the matching source text is to be handled.