#include <string>
#include <regex>
//some code
std::string string = "example@[0]pochta.com";
std::smatchs results;
if (std::regex_match(mess, results, std::regex(R"(^example@\[(\d+)\]pochta\.com$)")))
{
WORD number = std::itoa(results[1].str());
}
[code]