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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