Invoke function instead of macro in C

c, macros

Solution

If you have a function and a function-like macro both named `foo` and want to invoke the function version, you can do:

(foo)(args)

This works because function-like macro names must be followed by a parenthesized argument list for substitution to occur.

This is mentioned in section 7.1.4/1 of the ISO C99 standard:

Any function declared in a header may be additionally implemented as a function-like macro defined in the header, so if a library function is declared explicitly when its header is included, one of the techniques shown below can be used to ensure the declaration is not affected by such a macro. Any macro definition of a function can be suppressed locally by enclosing the name of the function in parentheses, because the name is then not followed by the left parenthesis that indicates expansion of a macro function name. For the same syntactic reason, it is permitted to take the address of a library function even if it is also defined as a macro. The use of `#undef` to remove any macro definition will also ensure that an actual function is referred to.

If you need to do this, though, you probably should add comments to your code explaining it since it looks a little weird and isn't common practice. If feasible, renaming the function to avoid the name collision might be more maintainable in the long run.

Problem

Original source