宏定义#井号的用法

单个井号（#）：在宏展开的时候会将#后面的参数替换成相应的字符串

#include <stdio.h>

#define Printi(message) printf(#message " = %d\n", message)
#define Printd(message) printf(#message " = %lf\n", message)
#define Prints(message) printf(#message " = %s\n", message)

int main(int argc, char *argv[])
{
int i_ = 10;
double d_ = 5.0;
char c[] = "hello";

Printi(i_);
Printd(d_);
Prints(c);

return 0;
}

两个井号（##）：起连接符的作用，将前后两个参数连接为一个子串，但连接后的子串不能当成字符串形式

#include <stdio.h>

#define Print(n) printf("token" #n " = %d\n", token##n)

int main(int argc, char *argv[])
{
int token1 = 10;

Print(1);

return 0;
}

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《C++ 编程思想》P95页

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#include <iostream>
using namespace std;

#define P(message) cout<< #message<<" = "<<message<<endl;

int main(int argc, char *argv[])
{
    int i_ = 10;
    double d_ = 5.0;
    string s_ = "hello";

    P(i_);
    P(d_);
    P(s_);

    return 0;
}

另可以参考：http://blog.csdn.net/morewindows/article/details/6697488