Infinite loop fscanf in C

Question

I am having problems with fscanf getting stuck in an infinite loop. {

char num;

FILE *filePtr;

if ((filePtr = fopen("filename.txt", "r")) == NULL)
{
    printf("File could not be opened");
}
else
{
    while (fscanf(filePtr, "%20[^ ,]", &num) != EOF)
    {
        displayFun(num);
    }

}

return 0;

The file input that I need it to read is: 0, 1, 2, 3, 16, 17, 1234, 5678, -201, 65534, 65535, 65536, -1

For some reason the code gets stuck in a loop and the first zero and wont continue on to the other numbers.

Your `fscanf` call will return `1` on success, so compare against that, not `EOF`. — melpomene, Jul 16 '16 at 21:39
I'm pretty sure you can't store 20 characters in a single `char`. — melpomene, Jul 16 '16 at 21:40
Possible duplicate of [Why is iostream::eof inside a loop condition considered wrong?](http://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-considered-wrong) — Eiko, Jul 16 '16 at 21:56
Also see http://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-considered-wrong — Eiko, Jul 16 '16 at 21:56
@Eiko That is a C++ answer. Please observe the tag system and don't close as duplicates from different languages. — 2501, Jul 16 '16 at 21:57
You get an infinite loop because when it comes across the comma, `scanf()` returns 0, not EOF. — Jonathan Leffler, Jul 17 '16 at 02:26

score 2 · Accepted Answer · edited May 23 '17 at 12:22

2

"%20[^ ,]" never consumes a , or space. They stay in filePtr for the next fscanf() call. Code needs to somehow read the , and space.

As @melpomene commented, reading text as a string into a char will not work,

Recommend to read an int and , instead.

int number;
while (fscanf(filePtr, "%d,", &number) == 1) {
    displayFun(num);
}

edited May 23 '17 at 12:22

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answered Jul 16 '16 at 21:44

chux - Reinstate Monica

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Infinite loop fscanf in C

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