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I'm working with a recent version of gcc, writing C++ code (but I would like an answer which would work for C as well). I have various extra warning flags enabled.

In my code, I am including a header from some popular library, #include <mylib.h>. Now, mylib.h triggers some of these compiler warnings; but I need to include it as-is, I can't alter it.

I want to suppress all compiler warnings when including mylib.h. I know I can suppress individual warnings with:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wwarning-name-here"
#pragma GCC diagnostic ignored "-Wanother-warning-name-here"

// my code goes here

#pragma GCC diagnostic pop

but I want to suppress all of the warnings. Can I do that? Note that I'm willing to tweak the compiler command-line if that helps.

Note: This related question indicates that, in 2015, one could not do this using pragmas.

einpoklum
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1 Answers1

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From GCC manual:

2.7 System Headers

The header files declaring interfaces to the operating system and runtime libraries often cannot be written in strictly conforming C. Therefore, GCC gives code found in system headers special treatment. All warnings, other than those generated by `#warning' (see Diagnostics), are suppressed while GCC is processing a system header. Macros defined in a system header are immune to a few warnings wherever they are expanded. This immunity is granted on an ad-hoc basis, when we find that a warning generates lots of false positives because of code in macros defined in system headers.

Normally, only the headers found in specific directories are considered system headers. These directories are determined when GCC is compiled. There are, however, two ways to make normal headers into system headers.

The -isystem command line option adds its argument to the list of directories to search for headers, just like -I. Any headers found in that directory will be considered system headers.

All directories named by -isystem are searched after all directories named by -I, no matter what their order was on the command line. If the same directory is named by both -I and -isystem, the -I option is ignored. GCC provides an informative message when this occurs if -v is used.

There is also a directive, #pragma GCC system_header, which tells GCC to consider the rest of the current include file a system header, no matter where it was found. Code that comes before the `#pragma' in the file will not be affected. #pragma GCC system_header has no effect in the primary source file.

how to make this happen in CMake?

From CMake manual:

include_directories

Add include directories to the build.

include_directories([AFTER|BEFORE] [SYSTEM] dir1 [dir2 ...])

...

If the SYSTEM option is given, the compiler will be told the directories are meant as system include directories on some platforms. Signalling this setting might achieve effects such as the compiler skipping warnings, or these fixed-install system files not being considered in dependency calculations - see compiler docs.

eerorika
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