ferror() -- STDIO Function (libc)

Discover stream status
#include <stdio.h>
int ferror(fp) FILE *fp;

ferror() tests the status of the  file stream fp. It returns a number other
than  zero if  an error  has occurred  on fp. Any  error condition  that it
discovers persists until you either  close the stream or call clearerr() to
clear it.  For write routines that employ buffers, call fflush() before you
call ferror(), in case an error occurs on the last block written.

Example

This example reads a word from one file and writes it into another.

#include <stdio.h>

main()
{
    FILE *fpin, *fpout;
    int inerr = 0;
    int outerr = 0;
    int word;
    char infile[20], outfile[20];

    printf("Name data file you wish to copy:\n");
    gets(infile);
    printf("Name new file:\n");
    gets(outfile);

    if ((fpin = fopen(infile, "r")) != NULL) {
        if ((fpout = fopen(outfile, "w")) != NULL) {

            for (;;) {
                word = fgetw(fpin);
                if (ferror(fpin)) {
                    clearerr(fpin);
                    inerr++;
                }

                if (feof(fpin))
                    break;
                fputw(word, fpout);
                if (ferror(fpout)) {
                    clearerr(fpout);
                    outerr++;
                }
            }

        } else {
            printf
                ("Cannot open output file %s\n",
                    outfile);
            exit(1);
        }

    } else {
        printf("Cannot open input file %s\n", infile);
        exit(1);
    }

    printf("%d - read error(s)  %d - write error(s)\n",
        inerr, outerr);
    exit(0);
}

See Also

libc
ANSI Standard, §7.9.10.3
POSIX Standard, §8.1

© 2012 by Stephen A. Ness