Nov 27, 2024 · #pragma is used to do something implementation-specific in C, i.e. be pragmatic for the current context rather than ideologically dogmatic. The one I regularly use is #pragma pack(1) where I'm trying to squeeze more out of my memory space on embedded solutions, with arrays of structures that would otherwise end up with 8 byte alignment.

Aug 3, 2017 · Pragma directives specify machine- or operating-specific compiler features. The __pragma keyword, which is specific to the Microsoft compiler, enables you to code pragma directives within macro definitions.

May 21, 2014 · #pragma is a preprocessor directive in its own right; it can't be used within a #define directive. So, this is why __pragma exists: it provides a way for a pragma to be issued from wherever the macro that uses it is expanded. This is a non-standard compiler extension (MSVC, Intel, and some C compilers support it to varying degrees). See also the _Pragma operator that is defined in newer ...

Aug 14, 2010 · #pragma comment is a compiler directive which indicates Visual C++ to leave a comment in the generated object file. The comment can then be read by the linker when it processes object files. #pragma comment(lib, libname) tells the linker to add the 'libname' library to the list of library dependencies, as if you had added it in the project properties at Linker->Input->Additional dependencies ...

Apr 25, 2011 · In the C and C++ programming languages, #pragma once is a non-standard but widely supported preprocessor directive designed to cause the current source file to be included only once in a single compilation. Thus, #pragma once serves the same purpose as #include guards, but with several advantages, including: less code, avoiding name clashes, and improved compile speed. See the Wikipedia ...

Aug 22, 2018 · #pragma pack instructs the compiler to pack structure members with particular alignment. Most compilers, when you declare a struct, will insert padding between members to ensure that they are aligned to appropriate addresses in memory (usually a multiple of …

Sep 24, 2010 · A pragma (from the Greek word meaning action) is used to direct the actions of the compiler in particular ways, but has no effect on the semantics of a program (in general).

According to wikipedia, some compilers optimize pragma once, some (like gcc) also optimize include guards. My gut says go with whatever system your code is already using. I use BOTH pragma once and guards.

Jul 11, 2010 · Use of any #pragma that is not defined in the C (or C++) standard renders your code non-portable. #pragma once is a bit of an exception in that it is one of the most commonly-implemented of the non-standard #pragma constructs. Its implementation, however, is not universal across standards-compliant compilers. #ifndef is.

Mar 15, 2012 · The syntax for the pragma in C could be: #pragma DATA_SECTION (symbol, "section name"); The syntax for the pragma in C++ could be: #pragma DATA_SECTION ("section name"); The DATA_SECTION pragma is useful if you have data objects that you want to link into an area separate from the .bss section.