^\s*\#include\s+["<]([^">]+)*[">]
You then want to look at the first capture group when you get a match. You don't say what language you're using, the factor you mention regcomp() leads me to believe that you're using POSIX regex library in C. If that's right, then you want to use the regexec function and use the nmatch and pmatch parameters to get the first capture group.
Type: match, Date: 7/12/2015 4:16:57 PMAuthor: stackoverflow
Replace multiple spaces example
Type: replace, Date: 7/12/2015 4:10:18 PMAuthor: stackoverflow
If Possible, Don't Use Regex To Validate Numbers. If at all possible, use your language. There may be functions to help you determine if the value contained by a string is a valid number. That being said, if you're accepting a variety of formats (commas, etc.) you may not have a choice.
Type: match, Date: 7/12/2015 4:07:04 PMAuthor: stackoverflow
Use ([0-9]+) if you need to match more than one digit (only Arabic numbers!).
Use (\d+) if you need all digits (all unicode digits).
Type: match, Date: 7/12/2015 4:00:33 PMAuthor: stackoverflow
Replace this Regex with an empty string + Compiled flag
Type: replace, Date: 7/12/2015 3:52:40 PMAuthor: stackoverflow