Suppresses warnings on unused entities.

[edit]Syntax

[edit]Explanation

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

• class:struct[[maybe_unused]] S;
• typedef, including those declared byalias declaration:[[maybe_unused]]typedef S* PS;,using PS[[maybe_unused]]= S*;
• variable, includingstatic data member:[[maybe_unused]]int x;
• non-static data member:union U{[[maybe_unused]]int n;};,
• function:[[maybe_unused]]void f();
• enumeration:enum[[maybe_unused]] E{};
• enumerator:enum{ A[[maybe_unused]], B[[maybe_unused]]=42};
• structured binding:[[maybe_unused]]auto[a, b]=std::make_pair(42,0.23);

For entities declared[[maybe_unused]], if the entities or their structured bindings are unused, the warning on unused entities issued by the compiler is suppressed.

[edit]Example

#include <cassert> [[maybe_unused]]void f([[maybe_unused]]bool thing1,[[maybe_unused]]bool thing2){[[maybe_unused]] lbl:// the label “lbl” is not used, no warning[[maybe_unused]]bool b= notfalse and nottrue;assert(b);// in release mode, assert is compiled out, and “b” is unused// no warning because it is declared [[maybe_unused]]}// parameters “thing1” and “thing2” are not used, no warning int main(){}

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit]References

[edit]See also

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