Thread: If user enters wrong information in scanf

>If a bastard user can't respect my program and input a Y or an N, he's going to hear it.
You don't have to type that much you know, just a little nice error message:

Code:

fprintf(stderr, "Um...I said Y or N. You didn't do either. Now I'll have to cast you into the bowels of hell. Have a nice day. :-)\n");
strlen(NULL);

>what is the strlen(NULL) for?
Smiting sinful users.

Originally Posted by Emmanuel Delaha

Sounds terrible to me. The "%s" will try to convert the input to a string. Imagine you just hit 'y'<ENTER>. You will get a 'y' at 'response', and a 0 at response + 1 (I assume you know what a C-string is). The problem is that response + 1 is not defined. Writing to an undefined memory location invokes an undefined behaviour. It's a serious bug.

At minimum, you want ;

Code:

	char response [2];

	scanf(" %s", response);

but using "%s" without a limit is dangerous (the gets() problem)

Code:

	scanf(" %1s", response);

but it's hard to maintain (but there are some ugly tricks). For all these reasons (among others), the good way to get a line from a user (or more generally from a stream) is to use fgets() or a smart function of yours based on it.

Well thank you for the correction. You explained it quite well actually.