Question

I’m trying to remove white spaces contained in a file and after I’ve read it using mmap, I proceed by removing white spaces by using a for-loop and shirting the next pointer to the current index but it doesnt seem to work. Here’s my code to illustrate:

static unsigned long get_size_by_fd(int fd) {
    struct stat statbuf;
    if(fstat(fd, &statbuf) < 0) exit(-1);
    return statbuf.st_size;
}

fd = open("/home/text.txt", O_RDONLY);
file_size = get_size_by_fd(fd);
fb = mmap(0, file_size, PROT_READ || PROT_WRITE, MAP_SHARED, fd, 0);

for (i = 0; i<file_size; i++) {
    if (fb[i] == 0x20) {
        fb[i] = fb[i++];
    }
}

Answer 1

There is no sequence point in the assignment fb[i] = fb[i++]; so you get unspecified results. Better to write it plainly:

if (fb[i] == 0x20 && i + 1 < file_size))
{
    fb[i] = fb[i + 1];
    ++i;
}

I also added an additional bounds check (consider when there are spaces at the end).

Note that your program makes assumptions on the file encoding.