What is the purpose of using the [^ notation in scanf?

Question

I have run into some code and was wondering what the original developer was up to. Below is a simplified program using this pattern:

      #include 

        

Answer 1

The constructs like %[a] and %[^a] exist so that scanf() can be used as a kind of lexical analyzer. These are sort of like %s, but instead of collecting a span of as many "stringy" characters as possible, they collect just a span of characters as described by the character class. There might be cases where writing %[a-zA-Z0-9] might make sense, but I'm not sure I see a compelling use case for complementary classes with scanf().

IMHO, scanf() is simply not the right tool for this job. Every time I've set out to use one of its more powerful features, I've ended up eventually ripping it out and implementing the capability in a different way. In some cases that meant using lex to write a real lexical analyzer, but usually doing line at a time I/O and breaking it coarsely into tokens with strtok() before doing value conversion was sufficient.

Edit: I ended ripping out scanf() typically because when faced with users insisting on providing incorrect input, it just isn't good at helping the program give good feedback about the problem, and having an assembler print "Error, terminated." as its sole helpful error message was not going over well with my user. (Me, in that case.)