CODEWITHSUNDEEP
cnewlineeoffgetc
John Smith
John Smith

Reputation: 13

Newline, EOF and feof() aren't acknowledged

I have a function that does the following:

ssize_t headache(char **lineptr, size_t *n, FILE * stream)
{
    if(lineptr != NULL)
    {
            free(*lineptr);
    }
    size_t  len     = 0,
            last    = 0;
    char *  buf     = NULL;
    int c;

    do
    { 
            last = len;
            ++len;
            buf = realloc(buf,len);
            c = fgetc(stream);
            buf[last] = (char)c;
            printf("%i\t%x\t%c\n", last, buf[last], buf[last]);
    }
    while(!feof(stream) || c != '\n');
    *n = strlen(buf);
    *lineptr = buf;
    return len;
}

headache is always called headache(&lineptr,&n,stream) where

char * lineptr = NULL;
size_t n = 0;
FILE * stream;

The do{}while(); loop will never acknowledge a newline or EOF, meaning that it will continue in infinity. I don't understand why is it ignoring EOF and '\n'. Can someone please tell me what did I do wrong?

Upvotes: 1

Views: 566

Answers (2)

rahul0705
rahul0705

Reputation: 41

Your issue is with

while(!feof(stream) || c != '\n')

this is because using || (or) you have to make both conditions false for it to stop execution. There are inputs that would make your while loop never end. this is a test input vs. this is a test input\n.

If you are running this as stdin as your file* compare what happens when you run it with you typing a message and pressing enter and you typing a message and pressing control-d (which is EOF in a terminal)

As stated by simonc you need the && operator which only requires one of the conditions to be false for it to stop.

Upvotes: 0

simonc
simonc

Reputation: 42175

while(!feof(stream) || c != '\n');

will loop again unless both conditions evaluate to false. You want to exit the loop when you either receive EOF or \n so should use && instead

while(!feof(stream) && c != '\n');

Upvotes: 3

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