Question

How to use C++ to get all the STDIN and parse it?

For example, my input is

2
1 4
3
5 6 7

I want to use C++ to read the STDIN using cin and store the each line in an array. So, it will be an vector/array of array of integers.

Thanks!

Answer 1

Since this isn’t tagged as homework, here’s a small example of reading from stdin using std::vectors and std::stringstreams. I added an extra part at the end also for iterating through the vectors and printing out the values. Give the console an EOF (ctrl + d for *nix, ctrl + z for Windows) to stop it from reading in input.

#include <iostream>
#include <vector>
#include <sstream>

int main(void)
{
   std::vector< std::vector<int> > vecLines;

   // read in every line of stdin   
   std::string line;
   while ( getline(std::cin, line) )
   {
      int num;
      std::vector<int> ints;
      std::istringstream ss(line); // create a stringstream from the string

      // extract all the numbers from that line
      while (ss >> num)
         ints.push_back(num);

      // add the vector of ints to the vector of vectors         
      vecLines.push_back(ints);      
   }

   std::cout << "\nValues:" << std::endl;
   // print the vectors - iterate through the vector of vectors   
   for ( std::vector< std::vector<int> >::iterator it_vecs = vecLines.begin();
         it_vecs != vecLines.end(); ++it_vecs )
   {
      // iterate through the vector of ints and print the ints
      for ( std::vector<int>::iterator it_ints = (*it_vecs).begin();
         it_ints < (*it_vecs).end(); ++it_ints )
      {
         std::cout << *it_ints << " ";
      }

      std::cout << std::endl; // new line after each vector has been printed
   }

   return 0;
}

Input/Output:

2
1 4
3
5 6 7

Values:
2 
1 4 
3 
5 6 7 

EDIT: Added a couple more comments to the code. Also note that an empty vectors of ints can be added to vecLines (from an empty line of input), that’s intentional so that the output is the same as the input.