ferror

Name

clearerr, feof, ferror, fileno
- check and reset stream status

Library

libc.lib

Synopsis

#include <stdio.h>

void clearerr (FILE *stream);

int feof (FILE *stream);

int ferror (FILE *stream);

int fileno (FILE *stream);

Detailed description

The function clearerr clears the end-of-file and error indicators for the stream pointed to by stream.

The function feof tests the end-of-file indicator for the stream pointed to by stream, returning non-zero if it is set. The end-of-file indicator can only be cleared by the function clearerr.

The function ferror tests the error indicator for the stream pointed to by stream, returning non-zero if it is set. The error indicator can only be reset by the clearerr function.

The function fileno examines the argument stream and returns its integer descriptor.

Examples

/****************** this program shows finding error set using ferror **************/
/****************** and clearing it using clearerr functions ***********************/
#include <stdio.h>
int main()
{
        char a;
        FILE* fp = fopen("c:\\input.txt", "w");
        fprintf(fp, "%s", "abcdefghijklmn");
        fprintf(fp, "%c", '\n');
        fprintf(fp, "%s", "fdsfdsafsdabcdefghijklmn");
        fclose(fp);
        fp=fopen("c:\\input.txt","r");
        if (fp == NULL)
                {
                printf("fopen failed\n");
                return -1;
                }
        else
                {
                fwrite(&a, sizeof(char), 1, fp);
                if (ferror (fp))
                        printf("error set in file stream\n");
                else
                        {
                        fclose(fp);
                        return -1;
                        }
                clearerr(fp);
                if (!ferror(fp))
                        printf("error cleared in file stream\n");
                else printf("error still unexpected set in file stream\n");
                fclose (fp);
                }
        return 0;
}

Output

error set in file stream
error cleared in file stream

Errors

These functions should not fail and do not set the external variable errno.

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