When should I use perror(“…”) and fprintf(stderr, “…”)?

Question

Reading the man pages and some code did not really help me in understanding the difference between - or better, when I should use - perror(\"...\") or fp

Answer 1

They do rather different things.

You use perror() to print a message to stderr that corresponds to errno. You use fprintf() to print anything to stderr, or any other stream. perror() is a very specialized printing function:

perror(str);

is equivalent to

if (str)
    fprintf(stderr, "%s: %s\n", str, strerror(errno));
else
    fprintf(stderr, "%s\n", strerror(errno));