Way better way of finding ints in strings

gistfile1.txt

int main() {
    std::string foostring = "this is a test [[6379]] of the number finding system.";
    auto digstart = foostring.find_first_of("1234567890");
    auto tail = foostring.substr(digstart);
    auto digend = tail.find_first_not_of("1234567890");
    auto digit = tail.substr(0,digend);
    auto digint = atoi(digit.c_str());
    std::cout << digint << std::endl;
    return 0;
}