写一段c代码,用预编译指令“if”,判断宏“__VAR”的值是不是被定义为了“user”
时间: 2023-06-02 13:04:07 浏览: 53
程序代码如下:
```c
#include <stdio.h>
#ifndef __VAR
#error "__VAR is not defined"
#endif
#ifndef user
#error "user is not defined"
#endif
int main() {
#ifdef __VAR
#if defined(__VAR) && __VAR == user
printf("__VAR is defined as user\n");
#else
printf("__VAR is defined but not as user\n");
#endif
#else
printf("__VAR is not defined\n");
#endif
return 0;
}
```
该代码首先检查`__VAR`是否被定义。如果没有被定义,则程序会显示一个错误消息。如果已定义,则检查其是否被定义为`user`。如果是,则程序输出`__VAR is defined as user`,否则输出`__VAR is defined but not as user`。如果`__VAR`未定义,则程序输出`__VAR is not defined`。