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!define
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Used to control compilation of a block of statements when the specified expression evaluates to true.
Syntax
[ !if expression | !ifdef identifier | !ifndef identifier ]
{ statement }...
{ [ !elif | !elseif ] expression
{ statement }... }...
{!else
{ statement }... }
!endif
Notes
!if
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Used when evaluating an expression.
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!ifdef
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Used to check if an identifier is defined.
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!ifndef
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Used to check if an identifier is not defined.
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!elif
!elseif
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Used when evaluating an expression. Only evaluated when the preceding
!if, !elif or !elseif directives evaluate to false.
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!else
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Used only used when the preceding !if, !ifdef, !ifndef,
!elif or !elseif directives evaluate to false.
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!endif
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Used to end !if, !ifdef and !ifndef directives.
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expression
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the expression to evaluate.
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identifier
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the identifier to check for existence.
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statement
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the statement(s) to compile when the preceding !if, !ifdef,
!ifndef, !elif or elseif evaluates to true.
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Example
!ifndef EOF
!define EOF (-1)
!endif
!if VERSION == 1
!include <v1sup.h>
!elif VERSION == 2
!include <v2sup.h>
!elif VERSION == 3
!include <v3sup.h>
!else
!error version not supported
!endif
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