谁知道sprintf是怎么实现的

[DDrddr]

在stdio.h中的声明是：
int _Cdecl sprintf (char *buffer, const char *format, ...);
后面的...是怎么处理的呢？

[new1mm]

/* Copyright (C) 1991, 1995, 1997, 1998, 2002 Free Software Foundation, Inc.
This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */

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

#ifdef USE_IN_LIBIO
# include <libio/iolibio.h>
# define vsprintf(s, f, a) INTUSE(_IO_vsprintf) (s, f, a)
#endif

/* Write formatted output into S, according to the format string FORMAT. */
/* VARARGS2 */
int
sprintf (char *s, const char *format, ...)
{
va_list arg;
int done;

va_start (arg, format);
done = vsprintf (s, format, arg);
va_end (arg);

return done;
}
libc_hidden_def (sprintf)

#ifdef USE_IN_LIBIO
strong_alias(sprintf, _IO_sprintf)
#endif

[Dragon132]

你运气真好，我刚好有一个例子

#include <stdio.h>
#include <stdlib.h>
#define MAX 20

int main(void)
{
char source[MAX];
char target[MAX];
char command[2*MAX+5];
puts("Enter the name of the file you wish to copy:");
gets(source);
puts("Enter the desired name for the copy:");
gets(target);
sprintf(command,"copy %s %s",source,target);

printf("Executing the following command: %s\n",command);
system(command);
return 0;
}

[Dragon132]

代码如下：

#ifndef _COUNT_

int __cdecl sprintf (
char *string,
const char *format,
...
)
#else /* _COUNT_ */

int __cdecl _snprintf (
char *string,
size_t count,
const char *format,
...
)
#endif /* _COUNT_ */

{
FILE str;
REG1 FILE *outfile = &str;
va_list arglist;
REG2 int retval;

va_start(arglist, format);

_ASSERTE(string != NULL);
_ASSERTE(format != NULL);

outfile->_flag = _IOWRT|_IOSTRG;
outfile->_ptr = outfile->_base = string;
#ifndef _COUNT_
outfile->_cnt = MAXSTR;
#else /* _COUNT_ */
outfile->_cnt = count;
#endif /* _COUNT_ */

retval = _output(outfile,format,arglist);

_putc_lk('\0',outfile); /* no-lock version */

return(retval);
}