Example/* VA.C: The program below illustrates passing a variable
* number of arguments using the following macros:
* va_start va_arg va_end
* va_list va_dcl (UNIX only)
*/#include <stdio.h>
#define ANSI /* Comment out for UNIX version */
#ifdef ANSI /* ANSI compatible version */
#include <stdarg.h>
int average( int first, ... );
#else /* UNIX compatible version */
#include <varargs.h>
int average( va_list );
#endifvoid main( void )
{
/* Call with 3 integers (-1 is used as terminator). */
printf( "Average is: %d\n", average( 2, 3, 4, -1 ) ); /* Call with 4 integers. */
printf( "Average is: %d\n", average( 5, 7, 9, 11, -1 ) ); /* Call with just -1 terminator. */
printf( "Average is: %d\n", average( -1 ) );
}/* Returns the average of a variable list of integers. */
#ifdef ANSI /* ANSI compatible version */
int average( int first, ... )
{
int count = 0, sum = 0, i = first;
va_list er; va_start( er, first ); /* Initialize variable arguments. */
while( i != -1 )
{
sum += i;
count++;
i = va_arg( er, int);
}
va_end( er ); /* Reset variable arguments. */
return( sum ? (sum / count) : 0 );
}
#else /* UNIX compatible version must use old-style definition. */
int average( va_alist )
va_dcl
{
int i, count, sum;
va_list er; va_start( er ); /* Initialize variable arguments. */
for( sum = count = 0; (i = va_arg( er, int)) != -1; count++ )
sum += i;
va_end( er ); /* Reset variable arguments. */
return( sum ? (sum / count) : 0 );
}
#endif
OutputAverage is: 3
Average is: 8
Average is: 0因为调用者知道传给函数多少个参数,所以他可以确定怎样清理堆栈,这样就可以实现可变参数了,你可以看看上边的例子
* number of arguments using the following macros:
* va_start va_arg va_end
* va_list va_dcl (UNIX only)
*/#include <stdio.h>
#define ANSI /* Comment out for UNIX version */
#ifdef ANSI /* ANSI compatible version */
#include <stdarg.h>
int average( int first, ... );
#else /* UNIX compatible version */
#include <varargs.h>
int average( va_list );
#endifvoid main( void )
{
/* Call with 3 integers (-1 is used as terminator). */
printf( "Average is: %d\n", average( 2, 3, 4, -1 ) ); /* Call with 4 integers. */
printf( "Average is: %d\n", average( 5, 7, 9, 11, -1 ) ); /* Call with just -1 terminator. */
printf( "Average is: %d\n", average( -1 ) );
}/* Returns the average of a variable list of integers. */
#ifdef ANSI /* ANSI compatible version */
int average( int first, ... )
{
int count = 0, sum = 0, i = first;
va_list er; va_start( er, first ); /* Initialize variable arguments. */
while( i != -1 )
{
sum += i;
count++;
i = va_arg( er, int);
}
va_end( er ); /* Reset variable arguments. */
return( sum ? (sum / count) : 0 );
}
#else /* UNIX compatible version must use old-style definition. */
int average( va_alist )
va_dcl
{
int i, count, sum;
va_list er; va_start( er ); /* Initialize variable arguments. */
for( sum = count = 0; (i = va_arg( er, int)) != -1; count++ )
sum += i;
va_end( er ); /* Reset variable arguments. */
return( sum ? (sum / count) : 0 );
}
#endif
OutputAverage is: 3
Average is: 8
Average is: 0因为调用者知道传给函数多少个参数,所以他可以确定怎样清理堆栈,这样就可以实现可变参数了,你可以看看上边的例子
cdecl调用可以实现变参,因为调用函数知道怎样清除栈中的参数,而pascal调用由函数自身负责就不可能变参了,因为函数不可能知道调用方串多少参数,所以不知道如何如何清理堆栈!