#运算符
#
运算符用于在预处理期将宏参数转换为字符串#
的转换作用是在预处理期完成的,因此只在宏定义中有效- 编译器不知道 # 的转换作用
■ 用法:
#define STRING(x) #x
printf("%s\n", STRING(Hello word));
实例分析: #运算符的基本用法
#include <stdio.h>
#define STRING(x) #x
int main()
{
printf("%s\n", STRING(Hello word));
printf("%s\n", STRING(100));
printf("%s\n", STRING(while));
printf("%s\n", STRING(return));
return 0;
}
输出:
Hello word
100
while
return
- gcc -E test.c -o test.i
Test_2.i
printf("%s\n", "Hello word");
printf("%s\n", "100");
printf("%s\n", "while");
printf("%s\n", "return");
实例分析: # 运算符的妙用
Test_2.c
#include <stdio.h>
#define CALL(f, p) (printf("Call funtion %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;
}
输出:
Call funtion square
result = 16
Call funtion func
result = 10
Test_2.i
result = (printf("Call funtion %s\n", "square"), square(4));
result = (printf("Call funtion %s\n", "func"), func(10));
##运算符
##
运算符用于在预处理期粘结两个标识符##
的连接作用是在预处理期完成的,因此只在宏定义中有效- 编译器不知道 ## 的连接作用
■ 用法:
#define CONNECT(a, b) a##b
int CONNECT(a, 1); // int a1
a1 = 2;
实例分析: ## 运算符的基本用法
Test_3.c
#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));
}
输出:
1
2
Test_3.i
int main()
{
int name1;
int name2;
name1 = 1;
name2 = 2;
printf("%d\n", name1);
printf("%d\n", name2);
}
实例分析:运算符的工程应用
Test_3.c
#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 = 1;
s2.name = "s2";
s2.id = 2;
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;
}
输出:
s1.name = s1
s1.id = 1
s2.name = s2
s2.id = 2
Test_4.i
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typedef struct _tag_Student Student; struct _tag_Student
{
char* name;
int id;
};
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