nestedFor

Loop through all permutations of some container.

For example, if you have a vector<vector<int>> as {{1, 2}, {3, 4}, {}, {5, 6}}, nestedFor iterates all 8 combinations.

Sample code:

#include "nestedFor.h"
#include <iostream>
#include <vector>

using namespace std;

int main()
{
    const std::vector<std::vector<int>>::size_type OUTER_VECTOR_SIZE = 4;
    const std::vector<int>::size_type INNER_VECTOR_SIZE = 2;

    vector<vector<int>> vec(OUTER_VECTOR_SIZE);

    int n = 0;

    for(auto& innerVec : vec)
    {
        // deliberately create a gap
        if(n == INNER_VECTOR_SIZE)
        {
            ++n;
            continue;
        }

        for(int m = 0; m < INNER_VECTOR_SIZE; ++m)
            innerVec.push_back(n++);
    }

    // output data structure JSON-like before
    for(auto& innerVec : vec)
    {
        std::cout << "{";
        for(auto& value : innerVec)
        {
            std::cout << value << ", ";
        }
        std::cout << "}";
    }

    std::cout << std::endl;

    // use nested for to create output
    nestedFor::run(vec.begin(), vec.end(),
                       [](const std::vector<int>& indices, const std::vector<int>& values){
                           for(int n = 0; n < values.size(); ++n)
                           {
                               if(indices[n] != -1)
                               {
                                   std::cout << values[n] << ", ";
                               }
                           }

                           std::cout << std::endl;
                       });

    return 0;
}

creates the output:

{0, 1, }{}{3, 4, }{5, 6, }
0, 3, 5, 
1, 3, 5, 
0, 4, 5, 
1, 4, 5, 
0, 3, 6, 
1, 3, 6, 
0, 4, 6, 
1, 4, 6, 

Notes

• C++11 required
• empty inner vectors are allowed, the corresponding index is -1, then
• you can easily modify the code to get iterators instead of indices and/or values in your callback function
• although you can leave out the const qualifiers in your callback, changing values has usually no reasonable effect
• although we use this function heavily, performance is not yet tested; especially due to indices and values given, a bare loop might be faster for some instances, you might need to test for yourself it is performance-critical