How to validate input using scanf

Question

How can I validate the user input by using scanf. Right now I have something like this, but doesn\'t work.

NOTE: I have the atoi just to validate that the scanf vali

Answer 1

What you specified in the first argument to scanf are conversion specifiers. scanf will try to convert the input to the format but sometimes you might be surprised what it will match against :)

The first check you should do is on the return value from scanf (it will give you the number of matching inputs). If you don't get the number you are expecting then you know that something is wrong with the input. In your case it should be 1.

if( scanf("%[0987654321.-]s", buf) == 1 )
{
      if( sanit_check( buf ) ) 
      {
      /* good input */
      }
      else
      {
      /* invalid input */
      }
}
else 
{
/* invalid input */
}

Beyond that you will need to do you own sanity checks on the conversion that you asked scanf to do.