Generating permuataions

[Script Coder]

I know how to generate all permutations of a list like:
{'h','e','k','p'}

But I am needing to know how to generate all permutations like:
{{'a','b'}, {'h','k','d'}, ..... }
such that the first character is either an 'a' or a 'b' and the second character is one of the three in the second list, etc.
There will be less than 600 000 permutations.

[Catfish666]

Nested for() loops? Of course there must exist a smarter way.

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#include <iostream> #include <string> int main() { std::string permutation(3, ' '); for (char c0: {'a', 'b'}) { permutation[0] = c0; for (char c1: {'h', 'k', 'd'}) { permutation[1] = c1; for (char c2: {'u', 'v', 'w'}) { permutation[2] = c2; std::cout << permutation << '\n'; } } } std::cout << std::endl; }

ahu ahv ahw aku akv akw adu adv adw bhu bhv bhw bku bkv bkw bdu bdv bdw

Edit: 600,000 permutations... hmm.

[JLBorges]

#include <iostream>
#include <iterator>
#include <vector>
#include <string>

template < typename ITERATOR >
void perms( std::string str, ITERATOR begin, ITERATOR end )
{
    if( begin != end )
        for( char c : *begin ) perms( str+c, std::next(begin), end ) ;
    else
    {
        static constexpr int WIDTH = 120 ;
        static int w = 0 ;

        w += str.size() + 3 ;
        if( w > WIDTH ) { std::cout << '\n' ; w = str.size() + 3  ; }
        std::cout << '"' << str << "\" " ;
    }
}

template < typename PERM_LIST > void perms( const PERM_LIST& list )
{ perms( "", list.begin(), list.end() ) ; }

int main()
{
    std::vector<std::string> perm_list = { "ab", "cdefg", "hij", "klmn", "opq", "rstuvw", "xyz" } ;
    perms( perm_list ) ;
}

http://coliru.stacked-crooked.com/a/c91ebb024f51de8b

[Script Coder]

Thank you guys very much.