C语言进阶课程学习记录-第25课 - # 和 ## 操作符使用分析

本文学习自狄泰软件学院 唐佐林老师的 C语言进阶课程，图片全部来源于课程PPT，仅用于个人学习记录

#运算符

实验-#转化字符串

#include <stdio.h>

#define STRING(x) #x

int main()
{
    
    printf("%s\n", STRING(Hello world!));
    printf("%s\n", STRING(100));
    printf("%s\n", STRING(while));
    printf("%s\n", STRING(return));

    return 0;
}
/*
output:
Hello world!
100
while
return
*/
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预处理后代码

//gcc -E test.c -o test.i
//test.i
# 1 "test.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "test.c"




int main()
{

    printf("%s\n", "Hello world!");
    printf("%s\n", "100");
    printf("%s\n", "while");
    printf("%s\n", "return");

    return 0;
}
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实验-#输出函数名

#include <stdio.h>

#define CALL(f, p) (printf("Call function %s\n", #f), f(p))
   
int square(int n)
{
    return n * n;
}

int func(int x)
{
    return x;
}

int main()
{
    int result = 0;
    
    result = CALL(square, 4);
    
    printf("result = %d\n", result);
    
    result = CALL(func, 10);
    
    printf("result = %d\n", result);

    return 0;
}
/*
output:
Call function square
result = 16
Call function func
result = 10
*/
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预处理后的代码

# 1 "test.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "test.c"




int square(int n)
{
    return n * n;
}

int func(int x)
{
    return x;
}

int main()
{
    int result = 0;

    result = (printf("Call function %s\n", "square"), square(4));//逗号表达式

    printf("result = %d\n", result);

    result = (printf("Call function %s\n", "func"), func(10));

    printf("result = %d\n", result);

    return 0;
}
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##运算符

实验-##定义变量

#include <stdio.h>

#define NAME(n) name##n

int main()
{
    
    int NAME(1);
    int NAME(2);
    
    NAME(1) = 1;
    NAME(2) = 2;
    
    printf("%d\n", NAME(1));
    printf("%d\n", NAME(2));

    return 0;
}
/*
output：
1
2

*/
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预处理后代码

int main()
{

    int name1;
    int name2;

    name1 = 1;
    name2 = 2;

    printf("%d\n", name1);
    printf("%d\n", name2);

    return 0;
}
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实验-##定义结构体

#include <stdio.h>

#define STRUCT(type) typedef struct _tag_##type type;\
                     struct _tag_##type

STRUCT(Student)
{
    char* name;
    int id;
};

int main()
{
    
    Student s1;
    Student s2;
    
    s1.name = "s1";
    s1.id = 0;
    
    s2.name = "s2";
    s2.id = 1;
    
    printf("s1.name = %s\n", s1.name);
    printf("s1.id = %d\n", s1.id);
    printf("s2.name = %s\n", s2.name);
    printf("s2.id = %d\n", s2.id);

    return 0;
}
/*
output：
s1.name = s1
s1.id = 0
s2.name = s2
s2.id = 1

*/
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预处理后的代码

# 1 "test.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "test.c"





typedef struct _tag_Student Student; struct _tag_Student
{
    char* name;
    int id;
};

int main()
{

    Student s1;
    Student s2;

    s1.name = "s1";
    s1.id = 0;

    s2.name = "s2";
    s2.id = 1;

    printf("s1.name = %s\n", s1.name);
    printf("s1.id = %d\n", s1.id);
    printf("s2.name = %s\n", s2.name);
    printf("s2.id = %d\n", s2.id);

    return 0;
}
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小结

#运算符用于在预处理期将宏参数转换为字符串

##运算符用于在预处理期粘连两个标识符

编译器不知道#和##运算符的存在

#和##运算符只在宏定义中有效