smatch | Regex (Regular Expressions) in C++
smatch is an instantiation of the match_results class template for matches on string objects. Functions that can be called using smatch: str(), position(), and length() member functions of the match_results object can be called to get the text that was matched, or the starting position and its length of the match relative to the subject string.
- Call these member functions without a parameter or with 0 as the parameter to get the overall regex match.
- Call them passing 1 or greater to get the match of a particular capturing group.
- The size() member function indicates the number of capturing groups plus one for the overall match.
- Thus you can pass a value up to size()-1 to the other three member functions(str(), position(), length() ).
What is capturing group ? Examples:
Example-1: Suppose you create a regex object like : regex re("(geeks)(.*)") Here no of capturing group is = 2 [ one is "geeks" and second is any character after "geeks" ]. Example-2: regex re("a(b)c") Here no of capturing group is = 1[ 'b' is the capturing group]. whatever within '(' and ')' braces is treated as capturing group.
Below is the program to show the working of smatch:
Match size = 3 Whole match : geeksforgeeks First capturing group is 'geeks' which is captured at index 0 Second capturing group is 'forgeeks' which is captured at index 5
Time Complexity: O(n)
Auxiliary Space: O(1)
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