error在c语言的用法,C语言进阶：23、#error和#line的用法
#error用于生成一个编译错误消息
用法：#error message
message不需要用双引号包围#error编译指示字用于自定义程序员特有的编译错误消息，类似的，#warning用于生成编译警告。
#error是一种预编译指示字，可用于提示编译条件是否满足#ifndef __cpluscplus //C++内置的宏 通过检测这个宏的存在，来进行错误提醒。
#error This file should be processed with C++ compiler
#endif
编译过程中任意错误信息意味着无法生成最终的可执行程序。#include
void f()
{
#if ( PRODUCT == 1 )
printf("This is a low level product!\n");
#elif ( PRODUCT == 2 )
printf("This is a middle level product!\n");
#elif ( PRODUCT == 3 )
printf("This is a high level product!\n");
#else
#warning The macro Product is NOT defined! //#error The macro Product is NOT defined!
#endif
}
int main()
{
f();
printf("1. Query Information.\n");
printf("2. Record Information.\n");
printf("3. Delete Information.\n");
#if ( PRODUCT == 1 )
printf("4. Exit.\n");
#elif ( PRODUCT == 2 )
printf("4. High Level Query.\n");
printf("5. Exit.\n");
#elif ( PRODUCT == 3 )
printf("4. High Level Query.\n");
printf("5. Mannul Service.\n");
printf("6. Exit.\n");
#endif
return 0;
}
运行输出：~/will$ gcc 23-2.c
23-2.c: In function ‘f’:
23-2.c:12: error: #error The macro Product is NOT defined!
将#error修改为warnning：~/will$ gcc 23-2.c
23-2.c: In function ‘f’:
23-2.c:12: warning: #warning The macro Product is NOT defined!
~/will$
~/will$ ./a.out
1. Query Information.
2. Record Information.
3. Delete Information.
条件编译：~/will$ gcc -DPRODUCT=3 23-2.c
~/will$ ./a.out
This is a high level product!
1. Query Information.
2. Record Information.
3. Delete Information.
4. High Level Query.
5. Mannul Service.
6. Exit.#line预处理器指示字
#line用于强制指定新的行号和编译文件名，并对源程序的代码重新编号。
用法：#line number filename
filename 可省略
#line编译指示字的本质是重定义 __FILE__ 和 __LINE__
行号从重新定义的文件名起始计算。(从最靠近主函数的地方开始计算)#include
// The code section is written by A.
// Begin
#line 1 "a.c"
// End
// The code section is written by B.
// Begin
#line 1 "b.c"
// End
// The code section is written by Delphi.
// Begin
#line 1 "willwilling's.c"
int main()
{
printf("%s : %d\n", __FILE__, __LINE__);
printf("%s : %d\n", __FILE__, __LINE__);
return 0;
}
// End
编译运行：~/will$ gcc 23-3.c
~/will$ ./a.out
willwilling's.c : 5
willwilling's.c : 7
小结：
#error用于自定义一条编译错误
#warning用于自定义一条编译警告信息
#error和#warning常用于条件编译的情形
#line用于强制指定新的行号和编译文件名。