Question

I need to read a string in a following order:

1. Read any amount of numbers separated by spaces, discard all but the last one, saving it to n
2. Read a space followed by n characters followed by space, save only the characters
3. Read two more numbers separated by spaces and save them as well

I thought of using string stream to read the numbers and stop at the string, but I don’t know how to predict a string in string stream and stop reading numbers without “reading” the string as number and killing the string stream.
How predict a string and stop reading numbers before it?
Is there a better way to read this whole pattern?
I use C++11.

Edit:
Example input:

1 2 3 4 6 abc de 7 8

Excepted output:

The string: 'abc de'
Number 1: 7
Number 2: 8

Answer 1

You can do that without using any regex, just by using standard C++ streams functionality. Here is an example using std::cin as input stream, but you can use a string stream if you want to read from a string.

#include <iostream>
#include <iomanip>
#include <vector>

int main(int argc, char* const argv[]) {

        int n,tmp;

        /// read integers, discarding all but the last
        while(std::cin >> tmp)
                n = tmp;
        if(std::cin.bad()) {
                std::cout << "bad format 1" << std::endl;
                return -1;
        }

        /// skip whitespaces
        std::cin >> std::ws;
        std::cin.clear();

        /// read a string of 'n' characters
        std::vector<char> buffer(n+1, '\0');
        if(! std::cin.read(buffer.data(), n) ) {
                std::cout << "bad format 2" << std::endl;
                return -1;
        }
        std::string s(buffer.data());

        /// Read 2 numbers
        int nb1, nb2;
        if(! (std::cin >> nb1 >> nb2)) {
                std::cout << "bad format 3" << std::endl;
                return -1;
        }

        std::cout << "The string: " << s << std::endl;
        std::cout << "Number 1: " << nb1 << std::endl;
        std::cout << "Number 2: " << nb2 << std::endl;
        return 0;
}