Question

gcc 4.4.2

I was reading an article about scanf. I personally have never checked the return code of a scanf.

#include <stdio.h>

int main(void)
{
  char buf[64];
  if(1 == scanf("%63s", buf))
  {
    printf("Hello %s\n", buf);
  }
  else
  {
    fprintf(stderr, "Input error.\n");
  }
  return 0;
}

I am just wondering what other techniques experienced programmers do when they use scanf when they want to get user input? Or do they use another function or write their own?

Thanks for any suggestions,

EDIT =========

#include <stdio.h>

int main(void)
{
    char input_buf[64] = {0};
    char data[64] = {0};

    printf("Enter something: ");
    while( fgets(input_buf, sizeof(input_buf), stdin) == NULL )
    {
    /* parse the input entered */
    sscanf(input_buf, "%s", data);
    }

    printf("Input [ %s ]\n", data);

    return 0;
}

I think most programmers agree that scanf is bad, and most agree to use fgets and sscanf. However, I can use fgets to readin the input. However, if I don’t know what the user will enter how do I know what to parse. For example, like if the user was to enter their address which would contain numbers and characters and in any order?

Answer 1

Don’t use scanf directly. It’s surprisingly hard to use. It’s better to read an entire line of input and to then parse it (possibly with sscanf).

Read this entry (and the entries it references) from the comp.lang.c FAQ:
http://c-faq.com/stdio/scanfprobs.html

Edit:
Okay, to address your additional question from your own edit: If you allow unstructured input, then you’re going to have to attempt to parse the string in multiple ways until you find one that works. If you can’t find a valid match, then you should reject the input and prompt the user again, probably explaining what format you want the input to be in.

For anything more complicated, you’d probably be better off using a regular expression library or even using dedicated lexer/parser toolkits (e.g. flex and bison).