function
<cstdio>

vsprintf

int vsprintf (char * s, const char * format, va_list arg );
Write formatted data from variable argument list to string
Composes a string with the same text that would be printed if format was used on printf, but using the elements in the variable argument list identified by arg instead of additional function arguments and storing the resulting content as a C string in the buffer pointed by s.

Internally, the function retrieves arguments from the list identified by arg as if va_arg was used on it, and thus the state of arg is likely to be altered by the call.

In any case, arg should have been initialized by va_start at some point before the call, and it is expected to be released by va_end at some point after the call.

Parameters

s
Pointer to a buffer where the resulting C-string is stored.
The buffer should be large enough to contain the resulting string.
format
C string that contains a format string that follows the same specifications as format in printf (see printf for details).
arg
A value identifying a variable arguments list initialized with va_start.
va_list is a special type defined in <cstdarg>.

Return Value

On success, the total number of characters written is returned.
On failure, a negative number is returned.

Example

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/* vsprintf example */
#include <stdio.h>
#include <stdarg.h>

void PrintFError ( const char * format, ... )
{
  char buffer[256];
  va_list args;
  va_start (args, format);
  vsprintf (buffer,format, args);
  perror (buffer);
  va_end (args);
}

int main ()
{
  FILE * pFile;
  char szFileName[]="myfile.txt";

  pFile = fopen (szFileName,"r");
  if (pFile == NULL)
    PrintFError ("Error opening '%s'",szFileName);
  else
  {
    // file successfully open
    fclose (pFile);
  }
  return 0;
}


In this example, if the file myfile.txt does not exist, perror is called to show an error message similar to:

Error opening file 'myfile.txt': No such file or directory


See also

vfprintf
Write formatted data from variable argument list to stream (function )
vprintf
Print formatted data from variable argument list to stdout (function )
sprintf
Write formatted data to string (function )
printf
Print formatted data to stdout (function )

C++