1. REGEX

2. Problems Have big text file, want to extract data Phone numbers
(503)

3. Regular Expressions Regular Expressions Pattern consists of
Format for specifying patterns
Pattern consists of
Literals
Ranges
Special values
Quantity indicators
Groupings

4. Literals Characters without special meaning are interpreted literally
Look for Look for A Look for 12A

5. Ranges [ ] enclose a group of options [123] Look for 1, 2, or 3
[AB] Look for A or B
2[BC] Look for 2 followed by B or C

6. Ranges [a-b] indicates a range [0-9] Look for 0-9 [1-3] Look for 1-3
[a-zA-Z] Look for lowercase a-z or upper
[0-9A-Z] digit or uppercase letter

7. Ranges [^ ] says not any of these [^123] Look for anything but 1,2,3
AA[^A] Look for 2 A's followed by anything not an A

8. Special Characters . Means any character but newline
A.C Matches ABC, ADC, A_C, A+C…

9. Special Characters ^ at start means nothing can be before
$ at end means nothing else after

10. Special Characters \s any whitespace \d any digit
Tab, space, etc…
\d any digit
Same as [0-9]
\w any word character
Same as [a-zA-Z]

11. Special Characters \S anything BUT whitespace \D anything BUT digit
\W anything BUT word character

12. Quantity Indicators {n} Must have n copies of whatever came before
\d{5} Match 5 digits
A{3}B Match 3 A's followed by a B

13. Quantity Indicators {n, m} n to m copies {n,} n or more copies
\d{2,5} Match 2 to 5 digits
{n,} n or more copies
{3,} Match any sequence of 3 or more digits

14. Quantity Indicators ? Indicates 0 or 1 + indicates 1 or more
A?B+C* could be:
BBBB, AB, ABBBC, ABCCCCC, B, BCCCC,…

15. \
\ to escape chars
\[ Find a [
\. Find a .
\\ Find a \

16. Grouping ( ) groups sequences Apply options to whole group
Can extract each group from results

17. |
| gives multiple options

18. Testing
QT Creator:

19. In C++ Part of c++11 Only partially implemented in current GCC
Available in boost xpression library