C++ <cstdio> - vfscanf() Function

The C++ <cstdio> vfscanf() function reads data from the stream, interprets it according to parameter format and stores the results into the locations pointed by the elements in the variable argument list identified by vlist.

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

In any case, vlist 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.

Syntax

• C++11

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

Parameters

Return Value

Returns number of receiving arguments successfully assigned (which may be zero in case a matching failure occurred before the first receiving argument was assigned), or EOF if input failure occurs before the first receiving argument was assigned.

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 a multibyte character encoding error occurs while interpreting wide characters, errno is set to EILSEQ.

Example: vfscanf() example

Lets assume that we have a file called employees.txt. This file contains following content:

John  25  3000
Marry 24  2750
Jo  27  2800
Kim 30  3100
Ramesh  28  3000

In the example below, the file is opened using fopen() function. Then the content of the file is parsed according to the specified format using vfscanf() function. After performing this operation, it is closed using fclose() function.

#include <cstdio>
#include <cstdarg>

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

int main (){
  char name [80];
  int age, salary;

  //open the file in read mode
  FILE *pFile = fopen("employees.txt", "r");

  //reads data from the file until EOF is reached
  while (!feof(pFile)) {
    ScanFormatted(pFile, "%s %i %i", name, &age, &salary);
    printf("%s is %i years old and earns %i dollars.\n", name, age, salary);
  }

  //closing the file
  fclose(pFile);

  return 0;
}

The output of the above code will be:

John is 25 years old and earns 3000 dollars.
Marry is 24 years old and earns 2750 dollars.
Jo is 27 years old and earns 2800 dollars.
Kim is 30 years old and earns 3100 dollars.
Ramesh is 28 years old and earns 3000 dollars.

Length sub-specifier

See <cinttypes> for the specifiers for extended types.