C attribute: maybe_unused (since C23)
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Suppresses warnings on unused entities.
Syntax
[[ maybe_unused ]][[ __maybe_unused__ ]]
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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
Run this code
#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); }