C ++，预处理器语句

Question

有人可以解释一下这句话的作用吗？

#define CONST_SIG (void (*) () ) 1

Answer 1

This statement defines CONST_SIG to be 1 cast into a pointer to a function that gets no parameters and returns void . This may be useful if you have a pointer to a function and you perhaps test it for truthness, then CONST_SIG will be true.

You can try the cdecl program, which is available in many linux distributions, for "English translation" of C declarations. Example output in this instance:

cdecl> explain (void (*) () )
cast unknown_name into pointer to function returning void

Side-note: The reason it says "unknown_name" is because our pointer has no name. To name it, for example, "p", would look like this: (void (*p) () ) .

Answer 2

您可以将CONST_SIG传递给需要函数指针的函数，并将值1视为此函数指针的特殊值。

Answer 3

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