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__has_c_attribute
The special operator __has_c_attribute (
operand)
may be
used in `#if' and `#elif' expressions in C code to test
whether the attribute referenced by its operand is recognized by
GCC in attributes using the `[[]]' syntax. GNU attributes must
be specified with the scope `gnu' or `__gnu__' with
__has_c_attribute
. When operand designates a supported
standard attribute it evaluates to an integer constant of the form
YYYYMM
indicating the year and month when the attribute was
first introduced into the C standard, or when the syntax of operands
to the attribute was extended in the C standard.