C语言#与##运算符的使用

#与##运算符的使用

1.#运算符

#define fun(x) #x  //将x转化成为字符串

//逗号表达式是从左往右进行计算
#define CALL(f, p) (printf("Call function %s\n", #f), f(p))

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

int f1(int x)
{
return x;
}

int main()
{
//对上面的宏进行测试
printf("%s\n", fun(hello world!));
printf("%s\n", fun(100));
printf("%s\n", fun(while));  //可以使用系统的命名
printf("%s\n", fun(return));

putchar(10);
printf("%d\n", CALL(square, 4));
printf("%d\n", CALL(f1, 10));

return 0;
}

gcc -E filename.c -o filename.i

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

int f1(int x)
{
return x;
}

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

putchar(10);
printf("%d\n", (printf("Call function %s\n", "square"), square(4)));
printf("%d\n", (printf("Call function %s\n", "f1"), f1(10)));

return 0;
}

2.##运算符

#define NAME(n) name##n

//对于结构体的定义且重命名以简化使用
#if 0
typedef struct TEST
{
int i;
int j;
}test;

//typedef TEST test;
#endif

//用宏定义来执行上述操作，可以简化操作且更普遍的适用
#define STRUCT(type) typedef struct TEST##type type;\
struct TEST##type

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

int main()
{
int NAME(1);
int NAME(2);

NAME(1) = 1;
NAME(2) = 2;

printf("%d\n", NAME(1));
printf("%d\n", NAME(2));

putchar(10);
student s1, 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;
}

gcc -E filename.c -o filename.i

typedef struct TESTstudent student;struct TESTstudent
{
char *name;
int id;
};
//可以在任何时候对结构体进行重命名，只要结构体被定义完成

int main()
{
int name1;
int name2;

name1 = 1;
name2 = 2;

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

putchar(10);
student s1, 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;
}