Thank you all for your replies, I can see that each have been carefully though out and well documented :) Tkil: With new concepts such as this, I often have trouble explaining myself. This is the exact same problem as the initial one, merely with a simpler explanation. My current thinking sees what I am doing as being outside the scope of regex, so I am planning to address the problem using just standard C++. Problem[1] - Compare 3 strings of text, if follows pattern[2] return s1.substr(text1+number) else return "" [2] Pattern is: s1.substr(text1+number)==s2.substr(text1+number-2)==s3.substr(text1+number-4) std::string answer=analyse(std::string("He ode 1"), std::string("Ze ode 3zczvsfd"), std::string("e ode 5")); So in this case the answer would equate to: "e ode 1" It seems to me that the only way to do this would be: 1. Search the 3 std::string for number, store number, length of number and position in a data-structure 2. Check if number in s1 == 2-number in s2 == 4-number in s3 3. If it does, find and the Longest Common Substring which includes the number, return the s1.substr LCS found 4. Else return "" I am thinking to piece this together using just the stdlib (std::isdigit &etc)... what do you think? Thanks for all suggestions, Alec Taylor [1]: Note that this is the same problem as my initial one stated, but I think this time I have figured out a completely unambiguous method of explaining both the pattern, input data, and expected results.