Pragma Directives 

#pragma token-string

Remarks

Each implementation of C and C++ supports some features unique to its host machine or operating system. Some programs, for instance, need to exercise precise control over the memory areas where data is placed or to control the way certain functions receive parameters. The #pragma directives offer a way for each compiler to offer machine- and operating system-specific features while retaining overall compatibility with the C and C++ languages. Pragmas are machine- or operating system-specific by definition, and are usually different for every compiler.

Pragmas can be used in conditional statements, to provide new preprocessor functionality, or to provide implementation-defined information to the compiler. The Microsoft C and C++ compilers recognize the following pragmas:

alloc_text	auto_inline	bss_seg
check_stack	code_seg	comment
component	conform1	const_seg
data_seg	deprecated	fenv_access
float_control	fp_contract	function
hdrstop	include_alias	init_seg1
inline_depth	inline_recursion	intrinsic
make_public	managed	message
omp	once	optimize
pack	pointers_to_members1	pop_macro
push_macro	region, endregion	runtime_checks
section	setlocale	unmanaged
vtordisp1	warning

1. Supported only by the C++ compiler.

The token-string is a series of characters that gives a specific compiler instruction and arguments, if any. The number sign (#) must be the first non-white-space character on the line containing the pragma; white-space characters can separate the number sign and the word pragma. Following #pragma, write any text that the translator can parse as preprocessing tokens. The argument to #pragma is subject to macro expansion.

If the compiler finds a pragma it does not recognize, it issues a warning, but compilation continues.

Some pragmas provide the same functionality as compiler options. When a pragma is encountered in source code, it overrides the behavior specified by the compiler option. For example, if you specified /Zp8, you can override this compiler setting for specific portions of the code with pack:

cl /Zp8 ...

<file> - packing is 8
// ...
#pragma pack(push, 1) - packing is now 1
// ...
#pragma pack(pop) - packing is 8
</file>

See Also

Other Resources

C/C++ Preprocessor Reference