C++ regex for overlapping matches

Question

I have a string \'CCCC\' and I want to match \'CCC\' in it, with overlap.

My code:

...
std::string input_seq = \"CCCC\";
std::regex re(\"CCC\");
std:         


        

Answer 1

Your regex can be put into the capturing parentheses that can be wrapped with a positive lookahead.

To make it work on Mac, too, make sure the regex matches (and thus consumes) a single char at each match by placing a . (or - to also match line break chars - [\s\S]) after the lookahead.

Then, you will need to amend the code to get the first capturing group value like this:

#include 
#include 
#include 
using namespace std;

int main() {
    std::string input_seq = "CCCC";
    std::regex re("(?=(CCC))."); // <-- PATTERN MODIFICATION
    std::sregex_iterator next(input_seq.begin(), input_seq.end(), re);
    std::sregex_iterator end;
    while (next != end) {
        std::smatch match = *next;
        std::cout << match.str(1) << "\t" << "\t" << match.position() << "\t" << "\n"; // <-- SEE HERE
        next++;
    }
    return 0;
}

See the C++ demo

Output:

CCC     0   
CCC     1