宏定义中#、##、#@和参数加括号

#include <stdio.h>

#define A(x, y)((x) * (y))
#define B(x, y)(x * y)

void main() {
    
    //非表达式参数
    printf("%d\n", A(11, 3));       //33    (11)*3
    printf("%d\n", B(11, 3));       //33    11*3

    //表达式参数
    printf("%d\n", A(6 + 5, 3));    //33    (6+5)*3
    printf("%d\n", B(6 + 5, 3));    //21    6+5*3

    //宏内的括号可以保证算术优先级，因为参数可能是表达式
}

 

#的作用是将其后的宏参数字符串化操作，就是在它引用的宏变量的左右各加上一个双引号
如#define f(a)#ab，传入5，展开后为"5"b

#include <stdio.h>

#define func(x, format) printf(#x" = %" #format "\n", x)

void main() {
    
    int g = 200;
    const char* c = "Hello";

    //printf("c"" = ""&s""\n", c);
    func(c, s);

    //printf("g"" = ""&d""\n", g);
    func(g, d);

    //因为C语言中，连续2个双引号会被编译器忽略
    
    //printf("c"" = ""&s""\n", c);
    //变为
    ////printf("c = &s\n", c);
}

 

##可以理解为两个#x，因为#x会自动在两侧添加双引号，所以##会添加两遍，也就等于没加，固##只是单纯的拼接

#include <stdio.h>

#define f(n, format, i)(printf(#n#i" = %"#format"\n", n##i))

void main() {
    
    int x1 = 1;
    int x2 = 10;
    int x3 = 100;
    int x4 = 1000;
    f(x, d, 1);
    f(x, d, 2);
    f(x, d, 3);
    f(x, d, 4);

    /*
    结果：
    x1 = 1
    x2 = 10
    x3 = 100
    x4 = 1000

    */
}