What are Stream Error Functions in C Language?

Question: What are Stream Error Functions in C Language?

Answer: We have functions in ANSI C specification which are used to determine the state of a stream. These are prototyped below,

    int feof(FILE *stream);
    int ferror(FILE *stream);
    void clearerr(FILE *stream);

‘feof()’ returns TRUE if stream is currently at end of file. Well! We have already seen that we can change current position in the file using fseek(), rewind() or fsetpos() functions. For ex.

To set to the beginning in a given stream,

    stream = fopen("file", "r");

or we can use

    fseek(stream, 0, SEEK_SET);

‘ferror()’ reports on error state of stream and returns TRUE if any read/write errors have occurred.

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/* ferror.c */
#include <stdio.h>
#include <stdlib.h>
#define SIZE 10
int main(void)
    FILE *stream;
    char buffer[SIZE];
    stream = fopen("hello.txt", "r");
    if (stream == NULL) {
        perror("File Open");
    /* read from the stream into buffer */
    fgets(buffer, SIZE, stream);
    /* check if there were any read/erite errors */
    if (ferror(stream))
        printf("Read/ Write Error.\n");
    return 0;

Finally, ‘clearerr()’ resets error indication on a given stream.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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