# 常用预定义宏

顾名思义，预定义宏就是已经预先定义好的宏，我们可以直接使用，无需再重新定义。

ANSI C 规定了以下几个预定义宏，它们在各个编译器下都可以使用：

- `__LINE__`：表示当前源代码的行号；
- `__FILE__`：表示当前源文件的名称；
- `__DATE__`：表示当前的编译日期；
- `__TIME__`：表示当前的编译时间；
- `__STDC__`：当要求程序严格遵循ANSI C标准时该标识被赋值为1；
- `__cplusplus`：当编写C++程序时该标识符被定义。

预定义宏查看。

```c
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[]){
    printf("Date: %s\n", __DATE__);
    printf("Time: %s\n", __TIME__);
    printf("File: %s\n", __FILE__);
    printf("Line: %d\n", __LINE__);
    
    system("pause");
    return 0;
}
```


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