# C attribute: maybe_unused (since C23)

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Suppresses warnings on unused entities.

### Syntax

`[[` `maybe_unused` `]]` `[[` `__maybe_unused__` `]]` |  |

### 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);
    }

### See also

C++ documentation for maybe_unused

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