Tag Archives: MEMVARBLOCK()
Variable Management Functions
Variable Management
| FieldBlock | Return a code block that sets/gets a value for a given field |
| FieldWBlock | Return a sets/gets code block for field in a given work area |
| HB_AParams | Returns an array containing values of all parameters passed to a function, method or procedure |
| HB_ArgC | Returns the number of command line arguments |
| HB_ArgCheck | Checks existence of an internal switch on the command line |
| HB_ArgShift | Updates HB_Arg* parameter list removing the 1-st one and replacing it by others |
| HB_ArgString | Retrieves the vale of an internal switch set on the command line. |
| HB_ArgV | Retrieves the value of a command line argument |
| HB_PIsByRef | Determine if a parameter is passed by reference. |
| HB_PValue | Retrieves the value of an argument. |
| HB_ValToStr | Converts any scalar type to a string. |
| MemVarBlock | Returns a codeblock that sets/gets a value of memvar variable |
| PCount | Retrieves the number of arguments passed to a function. |
| Type | Retrieves the type of an expression |
| ValType | Retrieves the data type of an expression |
MemVarBlock()
MEMVARBLOCK()
Returns a codeblock that sets/gets a value of memvar variable
Syntax
MEMVARBLOCK( <cMemvarName> ) --> <bBlock>
Arguments
<cMemvarName> – a string that contains the name of variable
Returns
<bBlock> a codeblock that sets/get the value of variable
Description
This function returns a codeblock that sets/gets the value of PRIVATE or PUBLIC variable. When this codeblock is evaluated without any parameters passed then it returns the current value of given variable. If the second parameter is passed for the codeblock evaluation then its value is used to set the new value of given variable – the passed value is also returned as a value of the codeblock evaluation.
Examples
PROCEDURE Main()
LOCAL cbSetGet
PUBLIC xPublic
cbSetGet := MEMVARBLOCK( "xPublic" )
EVAL( cbSetGet, "new value" )
? "Value of xPublic variable", EVAL( cbSetGet )
RETURN
Compliance
Clipper
Seealso
__MVGET(), __MVPUT()
Files
Library is rtl
FieldWBlock()
FIELDWBLOCK()
Return a sets/gets code block for field in a given work area
Syntax
FIELDWBLOCK( <cFieldName>, <nWorkArea> ) --> bFieldBlock
Arguments
<cFieldName> is a string that contain the field name.
<nWorkArea> is the work area number in which <cFieldName> exist.
Returns
FIELDWBLOCK() return a code block that when evaluate could retrieve field value or assigning a new value for a field in a given work area. If <cFieldName> is not specified or from type other than character, or if <nWorkArea> is not specified or is not numeric FIELDWBLOCK() return NIL.
Description
FIELDWBLOCK() return a code block that sets/gets the value of field from a given work area. When this code block is evaluated without any parameters passed then it returns the current value of the given field. If the code block is evaluated with a parameter, than its value is used to set a new value to the field, this value is also return by the block. If the block is evaluate and there is no field with the name <cFieldName> in work area number <nWorkArea>, the code block return NIL.
Examples
LOCAL bField
// this block work on the field "name" that exist on work area 2
bFiled := FIELDBLOCK( "name", 2 )
// open a file named One in work area 1
// that have a field named "name"
SELECT 1
USE one
// open a file named Two in work area 2
// it also have a field named "name"
SELECT 2
USE two
SELECT 1
? "Original names: ", One->name, Two->name
? "Name value for file Two :", EVAL( bField )
EVAL( bField, "Two has new name" )
? "and now: ", One->name, Two->name
Compliance
If the block is evaluate and there is no field with the name <cFieldName> in the given work area, the code block return NIL.
CA-Cl*pper would raise BASE/1003 error if the field does not exist.
Files
Library is rtl
Seealso
EVAL(), FIELDBLOCK(), MEMVARBLOCK()
FieldBlock()
FIELDBLOCK()
Return a code block that sets/gets a value for a given field
Syntax
FIELDBLOCK( <cFieldName> ) --> bFieldBlock
Arguments
<cFieldName> is a string that contain the field name.
Returns
FIELDBLOCK() return a code block that when evaluate could retrieve a field value or assigning a new value to the field. If <cFieldName> is not specified or from type other than character, FIELDBLOCK() return NIL.
Description
FIELDBLOCK() return a code block that sets/gets the value of field. When this code block is evaluated without any parameters passed then it returns the current value of the given field. If the code block is evaluated with a parameter, than its value is used to set a new value to the field, this value is also return by the block. If the block is evaluate and there is no field with the name <cFieldName> in the current work area, the code block return NIL.
Note that FIELDBLOCK() works on the current work area, if you need a specific work area code block use FIELDWBLOCK() instead.
Examples
// open a file named Test that have a field named "name"
LOCAL bField
bFiled := FIELDBLOCK( "name" )
USE Test
? "Original value of field 'name' :", EVAL( bField )
EVAL( bField, "Mr X new name" )
? "New value for the field 'name' :", EVAL( bField )
Compliance
If the block is evaluate and there is no field with the name <cFieldName> in the current work area, the code block return NIL.
CA-Cl*pper would raise BASE/1003 error if the field does not exist.
Files
Library is rtl
Seealso
EVAL(), FIELDWBLOCK(), MEMVARBLOCK()
C5_MEMVARBLOCK
MEMVARBLOCK()
Return a set-get code block for a given memory variable
------------------------------------------------------------------------------
Syntax
MEMVARBLOCK(<cMemvarName>) --> bMemvarBlock
Arguments
<cMemvarName> is the name of the variable referred to by the set-get
block, specified as a character string.
Returns
MEMVARBLOCK() returns a code block that when evaluated sets (assigns) or
gets (retrieves) the value of the given memory variable. If
<cMemvarName> does not exist, MEMVARBLOCK() returns NIL.
Description
The code block created by MEMVARBLOCK() has two operations depending on
whether an argument is passed to the code block when it is evaluated.
If evaluated with an argument, it assigns the value of the argument to
<cMemvarName>. If evaluated without an argument, the code block
retrieves the value of <cMemvarName>.
Notes
. MEMVARBLOCK() creates set-get blocks only for variables whose
names are known at runtime. MEMVARBLOCK(), therefore, cannot be used
to create set-get blocks for local or static variables. The same
restriction applies to creating blocks using the macro operator (&).
Examples
. This example compares MEMVARBLOCK() to a code block created
using the macro operator (&). Note that using MEMVARBLOCK() allows
you to avoid the speed and size overhead of the macro operator:
PRIVATE var := "This is a string"
//
// Set-Get block defined using macro operator
bSetGet := &( "{ |setVal|;
IF( setVal == NIL, var, var := setVal ) }" )
// Set-Get block defined using MEMVARBLOCK()
// bSetGet created here is the functional
// equivalent of bSetGet above
bSetGet := MEMVARBLOCK("var")
Files Library is CLIPPER.LIB.
See Also: FIELDBLOCK() FIELDWBLOCK()
Code blocks: what, where, and why?
C5 Variable Handling Commands
ACCEPT :
Place keyboard input into a memory variable
ACCEPT [<expPrompt>] TO <idVar>
CLEAR ALL* :
Close files and release public and private variables
CLEAR ALL
CLEAR MEMORY :
Release all public and private variables
CLEAR MEMORY
DECLARE* :
Create and initialize private memory variables and arrays
DECLARE <identifier> [[:= <initializer>], ... ]
FIELD :
Declare database field names
FIELD <idField list> [IN <idAlias>]
INPUT :
Enter the result of an expression into a variable
INPUT [<expPrompt>] TO <idVar>
LOCAL :
Declare and initialize local variables and arrays
LOCAL <identifier> [[:= <initializer>], ... ]
MEMVAR :
Declare private and public variable names
MEMVAR <idMemvar list>
MEMVARBLOCK() :
Return a set-get code block for a given memory variable
MEMVARBLOCK(<cMemvarName>) --> bMemvarBlock
PARAMETERS :
Create private parameter variables
PARAMETERS <idPrivate list>
PRIVATE :
Create and initialize private memory variables and arrays
PRIVATE <identifier> [[:= <initializer>], ... ]
PUBLIC :
Create and initialize public memory variables and arrays
PUBLIC <identifier> [[:= <initializer>], ... ]
RELEASE :
Delete public and private memory variables
RELEASE <idMemvar list>
RELEASE ALL [LIKE | EXCEPT <skeleton>]
RESTORE :
Retrieve memory variables from a memory (.mem) file
RESTORE FROM <xcMemFile> [ADDITIVE]
SAVE :
Save variables to a memory (.mem) file
SAVE TO <xcMemFile> [ALL [LIKE | EXCEPT <skeleton>]]
STATIC :
Declare and initialize static variables and arrays
STATIC <identifier> [[:= <initializer>], ... ]
STORE* :
Assign a value to one or more variables
STORE <exp> TO <idVar list>
<idVar> = <exp>
<idVar> := [ <idVar2> := ...] <exp>
