vscanf

vscanf

Read Formatted Input from the Standard Input Stream

Portability: C99

SYNOPSIS
DESCRIPTION
RETURN VALUE
IMPLEMENTATION
EXAMPLE
RELATED FUNCTIONS
SEE ALSO

SYNOPSIS

#include <stdarg.h>
#include <lcio.h>

int vscanf( const char *format, va_list arg );

DESCRIPTION

vscanf reads formatted input from stdin according to the format specified by the string format. Following the format in the argument list is a pointer to a list of arguments, designated by arg, of type va_list as defined in the header <stdarg.h>.

The string pointed to by format is in the same form as that used by fscanf. See the fscanf description for detailed information concerning the formatting conventions.

RETURN VALUE

vfscanf returns EOF if end of file (or an input error) occurs before any values are stored. If values are stored, it returns the number of items stored; that is, the number of times a value is assigned to a member of the variable argument list.

IMPLEMENTATION

vscanf is functionally equivalent to scanf, except that the argument list has been replaced by a variable argument list, va_list, as defined in the header <stdarg.h>.

EXAMPLE

#include <stdarg.h>
#include <lcio.h>
#include <stdlib.h>

int DoScan(const char *fmt, ...);

double point[40];

main()
{
   int index = 0;
   double sum = 0.0; 
   double avg;
   int nopoints;
   int stdn_fn = 0;

   /* If stdin is the terminal, fileno(stdin) is always 0. */
   if (isatty(stdn_fn))
      /* Tell user to enter data points; maximum = 39.        */
      puts("Enter data points (EOF to indicate end of list).");

   for(;;)
   {
      /* Read number; check for end of file.                  */
      if (DoScan("%le", &point[index]) == EOF)
         break;
      sum += point[index];
      ++index;
   }
   nopoints = index;
   avg = sum / nopoints;
   printf("%d points read.\n", nopoints);
   printf("%lf = average.\n", avg);
}

int DoScan(const char *fmt, ...)
{
   int n = 0;
   va_list args;

   va_start(args, fmt);
   n = vscanf(fmt, args);
   va_end(args);

   return n;
}

RELATED FUNCTIONS

vfprintf, scanf, va_arg, va_start, va_end

SEE ALSO

"I/O Functions" in Chapter 2, "Function Categories"
Chapter 3, "I/O Functions"

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