Extraction of integers from strings

Question

What is the best and shortest way to extract integers from a string and save them to an array of integers?

Sample string " 65 865 1 3 5 65 234 65 32 #$!@#"

I tried taking look at some other posts but couldn't find one about this specific issue... Some help and explanation would be great.

Answer 1

It seems this can all be done with std::stringstream:

#include <iostream>
#include <string>
#include <sstream>
#include <vector>
using namespace std;

int main() {
    std::string str(" 65 865 1 3 5 65 234 65 32 #$!@#");
    std::stringstream ss(str);
    std::vector<int> numbers;

    for(int i = 0; ss >> i; ) {
        numbers.push_back(i);
        std::cout << i << " ";
    }
    return 0;
}

---

Here is a solution that accounts for non digits between numbers:

#include <iostream>
#include <string>
#include <sstream>
#include <vector>
#include <algorithm>
using namespace std;

struct not_digit {
    bool operator()(const char c) {
        return c != ' ' && !std::isdigit(c);
    }
};

int main() {
    std::string str(" 65 865 1 3 5 65 234 65 32 #$!@# 123");
    not_digit not_a_digit;
    std::string::iterator end = std::remove_if(str.begin(), str.end(), not_a_digit);
    std::string all_numbers(str.begin(), end);
    std::stringstream ss(all_numbers);
    std::vector<int> numbers;

    for(int i = 0; ss >> i; ) {
        numbers.push_back(i);
        std::cout << i << " ";
    }
    return 0;
}

Answer 2

Because of the complexities of the delimiters here (you seem to have spaces and non-numeric characters) I'd use the string splitting available in the boost library:

http://www.boost.org/

This allows you to split using regular expressions as delimiters.

First, pick the delimiter which is a regular expression:

boost::regex delim(" "); // I have just a space here, but you could include other things as delimiters.

Then extract as follows:

std::string in(" 65 865 1 3 5 65 234 65 32 ");
std::list<std::string> out;
boost::sregex_token_iterator it(in.begin(), in.end(), delim, -1);
while (it != end){
    out.push_back(*it++);
}

So you can see I've reduced it to a list of strings. Let me know if you need to do the whole step to an array of integers (not sure what array type you want); happy to include that too if you want to go the boost way.