When using regex in C, \d does not work but [0-9] does

Question

I do not understand why the regex pattern containing the \\d character class does not work but [0-9] does. Character classes, such as \\s

Answer 1

\d is a perl and vim character class.

Use instead:

 const char *rstr = "^[[:digit:]]+\\s+\\w+\\s+[[:digit:]]+\\s+\\w+$";