retrieve arbitrary length strings from a given FILE stream

fgetline.c

#include <stdlib.h>

char*
fgetLine(FILE *stream)
{
    const size_t chunk = 128;
    size_t max = chunk;

    /* Preliminary check */
    if (!stream || feof(stream))
        return NULL;

    char *buffer = (char *)malloc(chunk * sizeof(char));
    if (!buffer) {
        perror("Unable to allocate space");
        return NULL;
    }
    char *ptr = buffer;
    int c;                      /* fgetc returns int. Comparing EOF w/ char may
                                 * cause issues. */
    while ( (c = fgetc(stream)) != EOF &&
            (*ptr = c) != '\n')
    {
        ++ptr;
        size_t offset = ptr - buffer;
        if (offset >= max) {
            max += chunk;

            char *tmp = realloc(buffer, max);
            if (!tmp) {
                free(buffer);
                return NULL;
            }
            buffer = tmp;
            ptr = tmp + offset;
        }
    }
    *ptr = '\0';
    return buffer;
}