How to disable GCC warnings for a few lines of code

Question

In Visual C++, it\'s possible to use #pragma warning (disable: ...). Also I found that in GCC you can override per file compiler flags. How can I do this for \"next line\",

Answer 1

Rather than silencing the warnings, gcc style is usually to use either standard C constructs or the __attribute__ extension to tell the compiler more about your intention. For instance, the warning about assignment used as a condition is suppressed by putting the assignment in parentheses, i.e. if ((p=malloc(cnt))) instead of if (p=malloc(cnt)). Warnings about unused function arguments can be suppressed by some odd __attribute__ I can never remember, or by self-assignment, etc. But generally I prefer just globally disabling any warning option that generates warnings for things that will occur in correct code.

Answer 2

It appears this can be done. I'm unable to determine the version of GCC that it was added, but it was sometime before June 2010.

Here's an example:

#pragma GCC diagnostic error "-Wuninitialized"
    foo(a);         /* error is given for this one */
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wuninitialized"
    foo(b);         /* no diagnostic for this one */
#pragma GCC diagnostic pop
    foo(c);         /* error is given for this one */
#pragma GCC diagnostic pop
    foo(d);         /* depends on command line options */

Answer 3

#define DIAG_STR(s) #s
#define DIAG_JOINSTR(x,y) DIAG_STR(x ## y)
#ifdef _MSC_VER
#define DIAG_DO_PRAGMA(x) __pragma (#x)
#define DIAG_PRAGMA(compiler,x) DIAG_DO_PRAGMA(warning(x))
#else
#define DIAG_DO_PRAGMA(x) _Pragma (#x)
#define DIAG_PRAGMA(compiler,x) DIAG_DO_PRAGMA(compiler diagnostic x)
#endif
#if defined(__clang__)
# define DISABLE_WARNING(gcc_unused,clang_option,msvc_unused) DIAG_PRAGMA(clang,push) DIAG_PRAGMA(clang,ignored DIAG_JOINSTR(-W,clang_option))
# define ENABLE_WARNING(gcc_unused,clang_option,msvc_unused) DIAG_PRAGMA(clang,pop)
#elif defined(_MSC_VER)
# define DISABLE_WARNING(gcc_unused,clang_unused,msvc_errorcode) DIAG_PRAGMA(msvc,push) DIAG_DO_PRAGMA(warning(disable:##msvc_errorcode))
# define ENABLE_WARNING(gcc_unused,clang_unused,msvc_errorcode) DIAG_PRAGMA(msvc,pop)
#elif defined(__GNUC__)
#if ((__GNUC__ * 100) + __GNUC_MINOR__) >= 406
# define DISABLE_WARNING(gcc_option,clang_unused,msvc_unused) DIAG_PRAGMA(GCC,push) DIAG_PRAGMA(GCC,ignored DIAG_JOINSTR(-W,gcc_option))
# define ENABLE_WARNING(gcc_option,clang_unused,msvc_unused) DIAG_PRAGMA(GCC,pop)
#else
# define DISABLE_WARNING(gcc_option,clang_unused,msvc_unused) DIAG_PRAGMA(GCC,ignored DIAG_JOINSTR(-W,gcc_option))
# define ENABLE_WARNING(gcc_option,clang_option,msvc_unused) DIAG_PRAGMA(GCC,warning DIAG_JOINSTR(-W,gcc_option))
#endif
#endif

This should do the trick for gcc, clang and msvc

Can be called with e.g.:

DISABLE_WARNING(unused-variable,unused-variable,42)
[.... some code with warnings in here ....]
ENABLE_WARNING(unused-variable,unused-variable,42)

see https://gcc.gnu.org/onlinedocs/cpp/Pragmas.html, http://clang.llvm.org/docs/UsersManual.html#controlling-diagnostics-via-pragmas and https://msdn.microsoft.com/de-DE/library/d9x1s805.aspx for more details

You need at least version 4.02 to use these kind of pragmas for gcc, not sure about msvc and clang about the versions.

It looks like the push pop pragma handling for gcc is a little bit broken. If you enable the warning again, you still get the warning for the block that was inside the DISABLE_WARNING/ENABLE_WARNING block. For some versions of gcc it works, for some it doesn't.

Answer 4

#pragma GCC diagnostic ignored "-Wformat"

Replace "-Wformat" with the name of your warning flag.

AFAIK there is no way to use push/pop semantics for this option.

Answer 5

For those who found this page looking for a way to do this in IAR, try this:

#pragma diag_suppress=Pe177
void foo1( void )
{
   /* The following line of code would normally provoke diagnostic 
      message #177-D: variable "x" was declared but never referenced.
      Instead, we have suppressed this warning throughout the entire 
      scope of foo1(). 
   */
   int x;
}
#pragma diag_default=Pe177

See http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0472m/chr1359124244797.html for reference.

Answer 6

To net everything out, this is an example of temporarily disabling a warning:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-result"
    write(foo, bar, baz);
#pragma GCC diagnostic pop

You can check the GCC documentation on diagnostic pragmas for more details.