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Showing content from https://www.cplusplus.com/reference/cstdio/vfscanf/ below:

function

vfscanf

int vfscanf ( FILE * stream, const char * format, va_list arg );

Read formatted data from stream into variable argument list

Reads data from the stream and stores them according to parameter format into the locations pointed by the elements in the variable argument list identified by arg.

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

stream: Pointer to a FILE object that identifies an input stream.
format: C string that contains a format string that follows the same specifications as format in scanf (see scanf 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 function returns the number of items of the argument list successfully filled. This count can match the expected number of items or be less (even zero) due to a matching failure, a reading error, or the reach of the end-of-file.

If a reading error happens or the end-of-file is reached while reading, the proper indicator is set (feof or ferror). And, if either happens before any data could be successfully read, EOF is returned.

If an encoding error happens interpreting wide characters, the function sets errno to EILSEQ.

Example

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

void ReadStuff (FILE * stream, const char * format, ...)
{
  va_list args;
  va_start (args, format);
  vfscanf (stream, format, args);
  va_end (args);
}

int main ()
{
  FILE * pFile;
  int val;
  char str[100];

  pFile = fopen ("myfile.txt","r");

  if (pFile!=NULL) {
    ReadStuff ( pFile, " %s %d ", str, &val );
    printf ("I have read %s and %d", str, val);
    fclose (pFile);
  }

  return 0;
}