为什么我会调用函数名称包含在parens中的函数？

Question

I recently came across code that looked like this:

void function(int a, int b, int c){
  //...
}

int main(){
  //...
  (function)(1,2,3);
  //...
}

What is the point of wrapping the function name separately in parens?
Does it have any affect that would be different than function(1,2,3); ?

Why does the language allow such syntax?

Answer 1

The only case I can think of where it would matter is when function is defined as a macro.

In C, standard library functions may also be implemented as function-like macros (for efficiency). Enclosing the function name in parentheses calls the actual function (since the function name is not followed by a ( ).

As for why the language allows the syntax, a function call consists of an expression of pointer-to-function type followed by the arguments in parentheses. In most cases, the prefix is a function name (which is implicitly converted to a pointer to the function), but it can be an arbitrary expression. Any expression may be enclosed in parentheses, usually without changing its meaning (other than affecting precedence). (But see Jonathan Leffler's comments for some counterexamples.)

Answer 2

In addition to suppressing function-like macro expansions, wrapping an unqualified function name in parentheses suppresses argument-dependent lookup . For example:

namespace meow {
    struct kitty {};
    void purr(kitty) {}
}

int main() {
    meow::kitty stl;
    purr(stl); // OK, ADL finds meow::purr
    (purr)(stl); // error; no ADL is performed
}