_Pragma is a preprocessing unary operator.
Syntax
_Pragma (string-literal)
_Pragma is a new preprocessing operator and is a part of C99
standards. The string literal is destringized by deleting the L prefix, if present. _Pragma deletes the leading
and trailing double quotes, replacing each escape sequence by a
double-quote, and replacing the escape sequence by a single backlash.
The resulting sequence of characters is processed to produce preprocessor
tokens that are executed as if they were preprocessed tokens in
a pragma directive.
The _Pragma operator provides portability in the use of an
existing #pragma C preprocessor construct. These pragmas are processed
as defined in its implementation. Most C implementations provide
pragmas that are very similar in meaning and functionality. The _Pragma operator can be used in the replacement text of
a macro, so as to aid in abstracting these specific pragmas a level
higher.
Examples |
 |
The following examples list the usage of the _Pragma operator:
Example 7-1 _Pragma
Operator Usage
A directive of the form,
#pragma listing on "..\listing.dir"
can also be expressed as,
_Pragma (listing on \"..\\listing.dir\"")
The latter form is processed as earlier, if it appears literally
as shown or it results from macro replacement, as in:
# define LISTING(x) PRAGMA(listing on #x)
# define PRAGMA(x) _Pragma(#x)
LISTING (..\listing.dir) |
Example 7-2 _Pragma
Operator Usage
_Pragma("ALIGN 4")
expands to
#pragma ALIGN 4
Example 7-3 _Pragma
Operator Usage
#define FOO "ALIGN 4"
_Pragma(FOO) |
expands to
#pragma ALIGN 4
