Get every regex match one by one with their positions - c++

Question

I need to get all regex matches and their positions.
For example, I have this regex:
std::regex r("(a)|(b)|(c)");
And this input text:
std::string text("abcab");
Now I want to loop the matches there in every loop I can access all occurrences from one match. So in first loop I could get "a" at position 0 and "a" at position 3. In second loop it'd be "b" at 1 and "b" at 4. And in third loop it'd be "c" at position 2. How can I do this?
Currently I have every regex part separately (regex for (a), (b) and (c)) and go through them one by one. But there are quite many of them so I'm looking for better/faster solution.

Answer 1

You can declare string vectors to store the captured values in, and then check which alternative branch matched, and add it to the corresponding vector.
Here is a C++ demo:
#include <string>
#include <iostream>
#include <regex>
using namespace std;
int main() {
std::regex r("(a)|(b)|(c)");
std::string s = "abcab";
std::vector<std::string> astrings; // Declare the vectors to
std::vector<std::string> bstrings; // populate with the contents
std::vector<std::string> cstrings; // of capturing groups
for(std::sregex_iterator i = std::sregex_iterator(s.begin(), s.end(), r);
i != std::sregex_iterator();
++i)
{
std::smatch m = *i;
if (m[1].matched) { // Check if Group 1 matched and
astrings.push_back(m[1].str()); // Put a value into a string vector
}
else if (m[2].matched) { // Check if Group 2 matched and
bstrings.push_back(m[2].str()); // Put a value into b string vector
}
else if (m[3].matched) { // Check if Group 3 matched and
cstrings.push_back(m[3].str()); // Put a value into c string vector
}
}
// Printing vectors - DEMO
for (auto i: astrings)
std::cout << i << ' ';
std::cout << "\n";
for (auto i: bstrings)
std::cout << i << ' ';
std::cout << "\n";
for (auto i: cstrings)
std::cout << i << ' ';
return 0;
}
You may also consider using std::regex_constants::optimize flag when declaring the regexp (see Galik's comment).