第23课 #error 和 #line 使用分析

//#include <stdio.h>

//因定义了类，所以该文件只能用C++编译器，而不能用C编译器编译
//C++命令行：g++ 23-1.c;
//C命令行编译：gcc 23-1.c, 但会出现＃error指示的错误！
#ifndef __cplusplus
    #error This file should be processed with C++ compiler
#endif

class CppClass
{
private:
    int m_nValue;
public:
    CppClass(){};
    ~CppClass(){};
};

int main()
{
    return 0;
}

#include <stdio.h>

//编译以下文件时，可测试PRODUCT未定义和定义两种不同情况
//带定义宏的编译命令行：gcc -DPRODUCT=3 23-2.c或gcc 23-2.c -DPRODUCT=3 
//不带宏的编译命令行：  gcc 23-2.c -o
void f()
{
#if (PRODUCT == 1)
    printf("This is a low level product!\n");
#elif (PROUDCT == 2)
    printf("This is a middle level product!\n");
#elif (PRODUCT == 3)
    printf("This is a high level product!\n");
#else
    #error The PRODUCT macro is NOT defined! //未定义PRODUCT宏时
#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. Mannual Service.\n");
    printf("6. Exit.\n");
#else
    #error The PRODUCT macro is NOT defined! //未定义PRODUCT宏时
#endif
    
    return 0;
}

#include <stdio.h>

//作者A写的代码
//--------------------------开始--------------------------
//把line的下一行定义为第1行，文件名为“a.c”
#line 1 "a.c"

//--------------------------结束--------------------------

//作者B写的代码
//--------------------------开始--------------------------
//把line的下一行定义为第1行，文件名为“b.c”
#line 1 "b.c"

//--------------------------结束--------------------------


//作者C写的代码
//--------------------------开始--------------------------
#line 1 "MyCode.c"

int main()
{
    printf("%s:%d\n",__FILE__,__LINE__);//输出MyCode.c:4

    #line 1 "Test.c"
    printf("%s:%d\n",__FILE__,__LINE__);//输出Test.c:1
    
    return 0;
}
//--------------------------结束--------------------------