16 #error 和 #line

目录

• 1 #error 的用法
• 2 #line 的用法

1 #error 的用法

• #error 用于生成一个编译错误信息

• 用法：#error 编译指示字用于自定义程序员特有的编译错误信息；类似的，#warning 用于生成编译警告，常用于条件编译的情形

  #error message
  message 不需要用双引号包围
  

• #error 是一种预编译器指示字

• #error 可用于提示编译条件是否满足

• 编译过程中的任何错误信息都意味着无法生成最终的可执行程序

  #include <stdio.h>
  
  #ifndef __cplusplus
      #error This file should be processed with C++ compiler.
  #endif
  
  class CppClass
  {
  private:
      int m_value;
  public:
      CppClass() {
          
      }
      
      ~CppClass() {
      }
  };
  
  int main()
  {
      return 0;
  }
  //使用gcc编译，输出信息
  test.c:4: error: #error This file should be processed with C++ compiler.
  

• #error 在条件编译中的应用

  #include <stdio.h>
  
  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
      #error The "PRODUCTY" 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;
  }
  
  //gcc: gcc -DPRODUCT=2 test.c
  This is a middle level product!
  1. Query Information.
  2. Record Information.
  3. Delete Information.
  4. High Level Query.
  5. Exit.
  
  //gcc: gcc -DPRODUCT=1 test.c
  This is a low level product!
  1. Query Information.
  2. Record Information.
  3. Delete Information.
  4. Exit.
  
  //gcc: gcc -DPRODUCT=3 test.c
  This is a high level product!
  1. Query Information.
  2. Record Information.
  3. Delete Information.
  4. High Level Query.
  5. Mannul Service.
  6. Exit.
  
  //gcc: gcc test.c
  test.c: In function 'f'
  test.c:12: error: #error The "PRODUCTY" is NOT defined!
  

2 #line 的用法

• #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 编译指示字的本质是重定义 __LINE__ 和 __FILE__

  #line number filename
  filename 可省略
  

• #line 的使用

  #include <stdio.h>
  
  // 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 C.
  // Begin
  #line 1 "main.c"
  
  
  int main()
  {
      printf("%s : %d\n", __FILE__, __LINE__);
      
      printf("%s : %d\n", __FILE__, __LINE__);
      
      return 0;
  }
  
  // End