C Programming Interview Question:

Why does everyone say not to use scanf? What should I use instead?

Submitted by: Administrator

scanf has a number of problems, its %s format has the same problem that gets() has --it's hard to guarantee that the receiving buffer won't overflow.
More generally, scanf is designed for relatively structured, formatted input (its name is in fact derived from ``scan formatted''). If you pay attention, it will tell you whether it succeeded or failed, but it can tell you only approximately where it failed, and not at all how or why. You have very little opportunity to do any error recovery.
Yet interactive user input is the least structured input there is. A well-designed user interface will allow for the possibility of the user typing just about anything--not just letters or punctuation when digits were expected, but also more or fewer characters than were expected, or no characters at all (i.e. just the RETURN key), or premature EOF, or anything. It's nearly impossible to deal gracefully with all of these potential problems when using scanf; it's far easier to read entire lines (with fgets or the like), then interpret them, either using sscanf or some other techniques. (Functions like strtol, strtok, and atoi are often useful; If you do use any scanf variant, be sure to check the return value to make sure that the expected number of items were found. Also, if you use %s, be sure to guard against buffer overflow.
Submitted by: Administrator