Function attributes are extensions implemented to enhance the portability of programs developed with GNU C. Specifiable attributes for functions provide explicit ways to help the compiler optimize function calls and to instruct it to check more aspects of the code. Others provide additional functionality.
A function attribute is specified with the keyword __attribute__ followed by the attribute name and any additional arguments the attribute name requires. A function __attribute__ specification is included in the declaration or definition of a function. The syntax takes the following forms:
Function attribute syntax: function declaration >>-function declarator--__attribute__---------------------------> .-,--------------------------. V | >--((----+-attribute_name---------+-+--))--;------------------->< '-__--attribute_name--__-'
The function attribute in a function declaration is always placed after the declarator, including the parenthesized parameter declaration:
/* Specify the attribute on a function prototype declaration */
void f(int i, int j) __attribute__((individual_attribute_name));
void f(int i, int j) { }In C++, the attribute specification must also follow any exception declaration that may be present for the function.
Due to ambiguities in parsing old-style parameter declarations, a function definition must have the attribute specification precede the declarator:
int __attribute__((individual_attribute_name)) foo(int i) { }
A function attribute
specification using the form __attribute_name__ (that
is, the attribute name with double underscore characters leading and
trailing) reduces the likelihood of a name conflict with a macro of
the same name.
The following function attributes are supported:
Related information