fgetpos()

Gets a stream's current file position indicator value.

  #include <stdio.h>
  
  int fgetpos(FILE *stream, fpos_t *pos);    

stream

A pointer to a file stream.

pos

A pointer to a file position.

The fgetpos() function is used in conjunction with the fsetpos() function to allow random access to a file. The fgetpos() function gives unreliable results when used with streams associated with a console ( stdin, stderr, stdout).

While the fseek() and ftell() functions use long integers to read and set the file position indicator, fgetpos() and fsetpos() use fpos_t values to operate on larger files. The fpos_t type, defined in stdio.h, can hold file position indicator values that do not fit in a long int.

The fgetpos() function stores the current value of the file position indicator for stream in the fpos_t variable pos points to.

This facility may have limited capability on configurations of the EWL that run on platforms that do not have console input/output or a file system.

fgetpos() returns zero when successful and returns a nonzero value when it fails.

#include <stdio.h>

#include <stdlib.h>

int main(void)

{

FILE *f;

fpos_t pos;

char filename[80], buf[80];

// get a filename from the user

printf("Enter a filename to read.\n");

gets(filename);

// open the file for input

if (( f = fopen(filename, "r")) == NULL) {

printf("Can't open %s.\n", filename);

exit(1);

}

printf("Reading each line twice.\n");

// get the initial file position indicator value

// (which is at the beginning of the file)

fgetpos(f, &pos);

// read each line until end-of-file is reached

while (fgets(buf, 80, f) != NULL) {

printf("Once: %s", buf);

// move to the beginning of the line to read it again

fsetpos(f, &pos);

fgets(buf, 80, f);

printf("Twice: %s", buf);

// get the file position of the next line

fgetpos(f, &pos);

}

// close the file

fclose(f);

return 0;

}

Output:

Enter a filename to read.

myfoo

Reading each line twice.

Once: chair table chest

Twice: chair table chest

Once: desk raccoon

Twice: desk raccoon