我如何解释这个宏？

Question

I really wonder what the return value of soap_strcpy is?

# define soap_strcpy(buf, len, src) (void)((buf) && (size_t)(len) > 0 && (strncpy((buf), (src), (len) - 1), (buf)[(len) - 1] = '\0'))

My tool reports the return value is always false. The last condition below is a kind of usual expression? How can I interpret it?

(strncpy((buf), (src), (len) - 1), (buf)[(len) - 1] = '\0'))

Answer 1

(strncpy((buf), (src), (len) - 1), (buf)[(len) - 1] = '\\0'))

Comma operator ? It's clearer now?

List of expressions, comma separated, the value of the expression is the one resulted by the evaluation of the last one in the list.

Since your last expression is an assignment with zero, of course it will always be zero. This doesn't mean the evaluation of the whole list is useless: first term copies, last term terminates the copy with the zero char.