How to determine end of file?

Question

FILE* cfl;
if ((cfl=fopen(csv, "r")) == NULL) {
    printf("Cannot open file for read.\r\n");
    exit(1);
}
while (!feof(cfl)) {
    int i = 0;
    char* buf = (char*)malloc(sizeof(char));
    while ((buf[i] = fgetc(cfl)) != '\n') {
        i++;
        buf = (char*)realloc(buf, sizeof(char)*(i+1));
        printf("=%d= ", i);
    }
    buf[i] = '\0';
    printf("+%d+ ", i);
    printf("%s\r\n", buf);
   free(buf);
}

fclose(cfl);

Everything works correctly to the last line. Since the file ends after the last line break, the program loops in while ((buf[i] = fgetc(cfl)) != '\n') {...}

I could interrupt the cycle after checking whether "i" does not exceed some large value, but it will be wrong. How to correctly determine the end of the file and why feof does not work in this case?

Read [Why is “while ( !feof (file) )” always wrong?](https://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong) — Andrew Henle, Aug 27 '18 at 12:14
You don't check for endof file at all in the inner while loop. — Jabberwocky, Aug 27 '18 at 12:15
Also, `fgetc()` returns `int`, not `char`. You can not reliably detect EOF if you read the results of `fgetc()` into a `char`. — Andrew Henle, Aug 27 '18 at 12:16
Not directly related to your problem, but reallocating a new buffer for every single char you're reading is very inefficient. You should reallocate chunks of, say, 64 kbytes at least. — Jabberwocky, Aug 27 '18 at 12:18
@Jabberwocky: For reading lines, 64 KB is huge. Maybe 1 KB or less would more typical, I’d expect. — Dietrich Epp, Aug 27 '18 at 13:48

score 7 · Accepted Answer · answered Aug 27 '18 at 12:15

7

The fgetc function returns an int, and the value will be EOF at end of file. This is the typical approach:

int c;
while ((c = fgetc(cfl)) != EOF) {
    ...
}

answered Aug 27 '18 at 12:15

Dietrich Epp

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Thanks. I will use this. It work fine for me. – Irbis Aug 27 '18 at 12:31
2

Note that you have to use feof to know if the EOF returned by fgetc mean "end of file" or "error". – Tom's Aug 27 '18 at 13:12

How to determine end of file?

1 Answers1