##的用法

今天看到一个问题关于##的，特意记录一下

出现在宏定义之中的##，用来告诉编译器，把两个字符串系在一起

参考例子:
// glue.c -- use the ## operator

#include <stdio.h>

#define XNAME(n) x ## n

#define PRINT_XN(n) printf("x" #n " = %d/n", x ## n);

int main(void)
{
int XNAME(1) = 14; // becomes int x1 = 14;

int XNAME(2) = 20; // becomes int x2 = 20;

PRINT_XN(1); // becomes printf("x1 = %d/n", x1);

PRINT_XN(2); // becomes printf("x2 = %d/n", x2);

return 0;
}

Here's the output:
x1 = 14
x2 = 20