from http://blog.csdn.net/pipisorry/article/details/25437893

C语言中没有參数默认值的概念，能够利用宏来模拟參数默认值:

(对于有多个參数的函数，调用时须要将參数列表中的每一个 " , "写出来，只是这样就能够把默认參数放在非默认參数之前)

下面代码在c下是不能通过的：

定义fun():

int fun(int a, int b = 10)                         ...                   ...

{                                             ....     ...           ...     ....

     return a+b;                                  

}                                                    ..                  ..

主函数代码：                                           ....        ....  

int main()                                                   ......

{

    printf("%d\n",fun(10));

    return 0;

}

..............................................................

编译时 fun(10) 调用会出错。注意这个代码在C++并不会错。

..............................................................

 

用宏改进后代码：

#include <stdio.h>

#define funi(a) fun( a, 10)

int fun(int a,int b )

{

        return a+b;

}

int main()

{

        int a = 10;

        printf("%d  %d\n",fun(a,10),funi(a));

        return 0;

}

结果： 20 20

 #include <stdio.h>

 #define DEFARG(name, defval) ((#name[0]) ? (name + 0) : defval)

 int _f1(int i)
 {
     return 2*i;
 }
 #define f1(arg0) _f1(DEFARG(arg0, 0))

 int _f2(int i, int j)
 {
     return i + j;
 }
 #define f2(arg0, arg1) _f2(DEFARG(arg0, 0), DEFARG(arg1, 1))

 int main()
 {
     printf("%d\n", f1());
     printf("%d\n", f1(1));

     printf("%d\n", f2(,));
     printf("%d\n", f2(2,));
     printf("%d\n", f2(, 3));
     printf("%d\n", f2(4, 5));
     return 0;
 }

from http://blog.csdn.net/pipisorry/article/details/25437893