How Can I Efficiently Extract Multiple Regex Matches from a String Using C \'s std::regex?

Matching Multiple Regex Results with std::regex

Matching multiple occurrences of a regular expression pattern in a string can be achieved using std::regex library. Consider a scenario where we want to extract every word from the string "first second third forth" in a single operation.

The initial attempt to use "(bS*b){0,}" did not yield the desired output because the repetition operator {0,} matches zero or more occurrences, including none, leading to empty matches.

To address this issue, we can employ a technique called lazy iteration. This involves iterating over the string while performing regex searches. Here's an example code:

#include <iostream>
#include <string>
#include <regex>

int main() {
    std::regex exp("(\b\S*\b)");
    std::smatch res;
    std::string str = "first second third forth";

    std::string::const_iterator searchStart(str.cbegin());
    while (std::regex_search(searchStart, str.cend(), res, exp)) {
        std::cout << (searchStart == str.cbegin() ? "" : " ") << res[0];
        searchStart = res.suffix().first;
    }
    std::cout << std::endl;
}

In this code, we loop through the string using searchStart, which represents the starting point of the next potential match. After each successful match, searchStart is updated to the end of the matched substring. This allows us to continue searching for subsequent matches until the entire string has been processed. The output of this code is:

first second third forth

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