C attribute: maybe_unused (since C23)

Suppresses warnings on unused entities.

Syntax

Explanation

This attribute can appear in the declaration of the following entities:

• struct / union : struct [ [ maybe_unused ] ] S ; ,
• typedef name : [ [ maybe_unused ] ] typedef S * PS ; ,
• object: [ [ maybe_unused ] ] int x ; ,
• struct/union member: union U { [ [ maybe_unused ] ] int n ; } ; ,
• function : [ [ maybe_unused ] ] void f ( void ) ; ,
• enumeration : enum [ [ maybe_unused ] ] E { } ; ,
• enumerator: enum { A [ [ maybe_unused ] ] , B [ [ maybe_unused ] ] = 42 } ; .

If the compiler issues warnings on unused entities, that warning is suppressed for any entity declared maybe_unused .

Example

#include <assert.h>
[[maybe_unused]] void f([[maybe_unused]] _Bool cond1, [[maybe_unused]] _Bool cond2)
{
   [[maybe_unused]] _Bool b = cond1 && cond2;
   assert(b); // in release mode, assert is compiled out, and b is unused
              // no warning because it is declared [[maybe_unused]]
} // parameters cond1 and cond2 are not used, no warning
int main(void)
{
    f(1, 1);
}

See also