gistfile1.txt

#include <iostream>
#include <vector>
#include <string>
#include <string_view>
#include <algorithm>

auto find_colons(std::string_view s) -> std::vector<std::size_t>
{
    std::vector<std::size_t> indices;
    auto it = s.begin();
    while ((it = std::find(it, s.end(), ':')) != s.end())
    {
        indices.emplace_back(std::distance(s.begin(), it++));
    }
    return indices;
}

auto find_digits(std::string_view s, const std::vector<std::size_t>& colon_indices) -> std::vector<std::string>
{
    std::vector<std::string> numbers;
    for (auto index : colon_indices)
    {
        index += 1;
        const auto start = s.begin() + index;
        if (const auto length = std::distance(start, std::find_if_not(start, s.end(), std::isdigit));
            length)
        {
            numbers.emplace_back(s.substr(index, length));
        }
    }
    return numbers;
}

int main()
{
    std::string s = "hello:123world:1488:!";
    for (auto i : find_digits(s, find_colons(s)))
        std::cout << i << '\n';
    std::cout << s << std::endl;
}