c语言重载(overriding in C)或函数不定参数个数

google一下 c overiding发现有这样一段英文解释：

Because C doesn't require that you pass all parameters to the function if you leave the parameter list blank in the prototype. The compiler should only throw up warnings if the prototype has a non-empty parameter list and you don't pass enough enough arguments to the function.

在c语言里面如果函数原型参数列表为空，编译器不会要求你把所有参数传递给函数。

如果编译器发现函数原型参数列表非空，并且没有传递足够的参数给函数，他应该仅仅只抛出一个警告。

itsme@dreams:~/C$ cat param.c
#include <stdio.h>

void func();

int main(void)
{
  func();
  func(, );

  return ;
}

void func(int a, int b)
{
  if(a == )
    puts("Only going to use first argument.");
  else
    printf("Using both arguments: a = %d, b = %d\n", a, b);
}
itsme@dreams:~/C$ gcc -Wall -ansi -pedantic param.c -o param
itsme@dreams:~/C$ ./param
Only going to use first argument.
Using both arguments: a = , b =

actually fcnt is defined in the header file using 
int fcntl (int fd, int cmd, ...);
This means it can take variable number of arguments. 
now it looks at the command and then decides if anything follows as the third parameter or not.
see man va_arg etc for more details.

通常函数fcnt在头文体以int fcntl (int fd, int cmd, ...)方式定义，意味着他可以接受不定个数的参数,

你可以在linux下通过man va_arg等等查看详情。

#include <stdio.h>
#include <stdarg.h>

void printargs(int args1,...)//输出所有的int类型的参数，直到-1结束
{
    va_list ap;
    int i;

    va_start(ap,args1);
    for (i = args1; i != -; i =va_arg(ap,int))
    printf("%d ",i);
    va_end(ap);
    putchar('\n');
}

int main(void)
{
    printargs(,,,,,,,,-);
    printargs(,,-);
    printargs(-);
    printargs(,-);
    return ;
}