L20#和##使用
1. #
#include <stdio.h>
#define CALL(f, p) (printf("Call function %s\n", #f), f(p))
int square(int n)
{
return n * n;
}
int f(int x)
{
return x;
}
int main()
{
printf("1. %d\n", CALL(square, 4));
printf("2. %d\n", CALL(f, 10));
return 0;
}
作用: #在宏定义中将后面的任何元素转换为一个字符串
2. ##
作用: ##用于在预编译期粘连两个符号
范例:结构体定义
#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("%s\n", s1.name);
printf("%d\n", s1.id);
printf("%s\n", s2.name);
printf("%d\n", s2.id);
return 0;
}