为什么以下函数被调用三次

Question

我曾尝试调试,但没有运气我不明白为什么第二个printf()调用increment()三次,但第一个调用两次按预期.

#include <stdio.h>

#define MAX(a, b) ( (a) > (b) ? (a) : (b) )

int increment(){
    static int i = 42;
    i += 5;
    printf("increment returns %d\n", i); // 47, 52, 57
    return i;
}

int main( int argc, char ** argv ) {
    int x = 50;
    // parameters compute from right to left side
    printf("max of %d and %d is %d\n",
                x, //3rd: 50
                increment(), //2nd: 52
                MAX(x, increment()) //1st: 50,47 -> 50
                );

    printf("max of %d and %d is %d\n",
                x, //3rd: 50
                increment(), //2nd: 62
                MAX(x, increment()) //1st: 50,57 -> 57
                );
    return 0;
}

结果

increment returns 47
increment returns 52
max of 50 and 52 is 50
increment returns 57
increment returns 62
increment returns 67
max of 50 and 67 is 62

Answer 1

因为你告诉它:

MAX(x, increment())

评估为

( (x) > (increment()) ? (x) : (increment()) )

如果条件未满足,:则评估后的部分,从而再次调用该函数.