Node:fscanf, Previous:Deprecated formatted string input functions, Up:String output and input

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fscanf

The fscanf function is just like the scanf function, except that the first argument of fscanf specifies a stream from which to read, whereas scanf can only read from standard input.

Here is a code example that generates a text file containing five numbers with fprintf, then reads them back in with fscanf. Note the use of the # flags in the %#d conversions in the fprintf call; this is a good way to generate data in a format that scanf and related functions can easily read with the %i input conversion.

#include <stdio.h>
#include <errno.h>

int main()
{
  float f1, f2;
  int i1, i2;
  FILE *my_stream;
  char my_filename[] = "snazzyjazz.txt";

  my_stream = fopen (my_filename, "w");
  fprintf (my_stream, "%f %f %#d %#d", 23.5, -12e6, 100, 5);

  /* Close stream; skip error-checking for brevity of example */
  fclose (my_stream);

  my_stream = fopen (my_filename, "r");
  fscanf (my_stream, "%f %f %i %i", &f1, &f2, &i1, &i2);

  /* Close stream; skip error-checking for brevity of example */
  fclose (my_stream);

  printf ("Float 1 = %f\n", f1);
  printf ("Float 2 = %f\n", f2);
  printf ("Integer 1 = %d\n", i1);
  printf ("Integer 2 = %d\n", i2);

  return 0;
}

This code example prints the following output on the screen:

Float 1 = 23.500000
Float 2 = -12000000.000000
Integer 1 = 100
Integer 2 = 5

If you examine the text file snazzyjazz.txt, you will see it contains the following text:

23.500000 -12000000.000000 100 5