Question

This is a working snippet of a while loop:

while(total_bytes_read != fsize){
    while((nread = read(sockd, filebuffer, sizeof(filebuffer))) > 0){
        if(write(fd, filebuffer, nread) < 0){
            perror("write");
            close(sockd);
            exit(1);
        }
        total_bytes_read += nread;
        if(total_bytes_read == fsize) break;
    }
}

This is an example of a NON working snippet of a while loop:

while(total_bytes_read != fsize){
    while((nread = read(sockd, filebuffer, sizeof(filebuffer))) > 0){
        if(write(fd, filebuffer, nread) < 0){
            perror("write");
            close(sockd);
            exit(1);
        }
        total_bytes_read += nread;
    }
}

And also this, is an example of a NON working snippet of a while loop:

while(total_bytes_read < fsize){
    while((nread = read(sockd, filebuffer, sizeof(filebuffer))) > 0){
        if(write(fd, filebuffer, nread) < 0){
            perror("write");
            close(sockd);
            exit(1);
        }
    }
     total_bytes_read += nread;
}

I would like to know why into the 2 snippet above when total_bytes_read is equal to fsize the loop won’t exit :O
Thanks in advance!

Answer 1

The outer loop in snippets 2 and 3 will not exit because the inner loop does not exit: the total_bytes_read != fsize loop never gets a chance to check its continuation condition.

Snippet 1 works fine, because you check the same condition inside the nested loop, and break out if the limiting count has been reached.

You can combine both conditions into a single loop, like this:

while((total_bytes_read != fsize) && (nread = read(sockd, filebuffer, sizeof(filebuffer))) > 0) {
    ...
}