看好多开源代码里都用到了宏定义的函数编程，这里写个demo体验一下。

如下代码输出0

#ifndef __PRINT_0_
#define __PRINT_0_

#include <stdio.h>
int defineFunc(){
    int x;
#ifdef __PRINT_0_
    x = 0;
#else
    x = 1;
#endif
    return x;
}
int main(){
    int res = defineFunc();
    printf("%d\n", res);
    return 0;
}

#endif

如下代码输出1

#include <stdio.h>
int defineFunc(){
    int x;
#ifdef __PRINT_0_
    x = 0;
#else
    x = 1;
#endif
    return x;
}
int main(){
    int res = defineFunc();
    printf("%d\n", res);
    return 0;
}