Using regex to parse out numbers - c++

Question

My problem is more or less self-explanatory, I want to write a regex to parse out numbers out of a string that user enters via console. I take the user input using:
getline(std::cin,stringName); //1 2 3 4 5
I asume that user enters N numbers followed by white spaces except the last number.
I have solved this problem by analyzing string char by char like this:
std::string helper = "";
std::for_each(stringName.cbegin(), strinName.cend(), [&](char c)
{
if (c == ' ')
{
intVector.push_back(std::stoi(helper.c_str()));
helper = "";
}
else
helper += c;
});
intVector.push_back(std::stoi(helper.c_str()));
I want to achieve the same behavior by using regex. I've wrote the following code:
std::regex rx1("([0-9]+ )");
std::sregex_iterator begin(stringName.begin(), stringName.end(), rx1);
std::sregex_iterator end;
while (begin != end)
{
std::smatch sm = *begin;
int number = std::stoi(sm.str(1));
std::cout << number << " ";
}
Problem with this regex occurs when it gets to the last number since it doesn't have space behind it, therefore it enters an infinite loop. Can someone give me an idea on how to fix this?

Answer 1

You're going to get an endless loop there because you never increment begin. If you do that, you'll get all the numbers except the last one (which, as you say, is not followed by a space).
But I don't understand why you feel it necessary to include the whitespace in the regular expression. If you just match a string of digits, the regex will automatically select the longest possible match, so the following character (if any) cannot be a digit.
I also see no value in the capture in the regex. If you wanted to restrict the capture to the number itself, you would have used ([0-9]+). (But since stoi only converts until it finds a non-digit, it doesn't matter.)
So you just use this:
std::regex rx1("[0-9]+");
for (auto it = std::sregex_iterator{str.begin(), str.end(), rx1},
end = std::sregex_iterator{};
it != end;
++it) {
std::cout << std::stoi(it->str(0)) << '\n';
}
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