C++ map to track when the end of map is reached

Question

Currently I have a map that prints out the following

map<string, map<int,int> > mapper;
map<int,int>::iterator inner;
map<string, map<int,int> >::iterator outer;


for(outer = mapper.begin(); outer != mapper.end(); outer++){
    cout<<outer->first<<": ";
  for(inner = outer->second.begin(); inner != outer->second.end(); inner++){
      cout<<inner->first<<","<<inner->second<<",";
  }
}

As of now this prints out the following

  stringone: 1,2,3,4,6,7,8,
  stringtwo: 3,5,6,7,
  stringthree: 2,3,4,5,

What i want it to print out is

  stringone: 1,2,3,4,6,7,8
  stringtwo: 3,5,6,7
  stringthree: 2,3,4,5

how can i check for the end of the map inside my inner map? Any help would be appreciated Thank you

Answer 1

You could store the result in a string for example and trim the last character after the for.

Answer 2

Change your output line to print the comma first and only if it is not the first element:

if (inner != outer->second.begin())
    std::cout << ",";
std::cout << inner->first << "," << inner->second;

Answer 3

You need to modify your inner loop so that it prints the comma separator at the start for each iteration other than the first, something like:

// inside the loop
cout << ( inner == outer->second.begin() ? "" : "," ) << inner->first << "," << inner->second;

Answer 4

You have specified how you want to solve your problem technically 'finding the end of the loop' but the formatting you are trying to resolve can be managed in other ways.

Unroll the inner loop, and move the seperator.

for(m = mapper.begin(); m != mapper.end(); m++){
    cout<<m->first<<": ";

  if( inner = m->second.begin() != m->second.end() ) {
    cout<<inner->first<<","<<inner->second;
    ++inner
    for(; inner != m->second.end(); ++inner){
      cout<<","<<inner->first<<","<<inner->second;
    }
  }
}

This means you don't have to do a in if test in each iteration of the loop

Answer 5

I'd change it to use std::copy, which I'd use along with an infix_ostream_iterator.

Edit: I'd also note for the record that what you're doing looks an awful lot like an std::multimap. If you don't want to use a multimap, it still looks like a lot simpler way to go would be something like:

std::ostream &operator<<(std::ostream &os, std::vector<int> const &v) { 
    std::copy(v.begin(), v.end(),
              infix_ostream_iterator<int>(os, ","));
    return os;
}

std::map<std::string, std::vector<int> > mapper;

std::copy(mapper.begin(), mapper.end(), 
          std::ostream_iterator<std::vector<int> >(std::cout, "\n");

Answer 6

  for(inner = m->second.begin(); inner != m->second.end(); inner++){ 
      cout<<inner->first<<","<<inner->second;
      if (next(inner) != m->second.end()){
          cout<<",";
      }
  } 

Edit: It has been pointed out that map::iterator doesn't support addition, and that a suitable substitute is a nonstandard next function. I've updated the above code, and here's my own version of next.

template<typename T>
T next(T incrementable)
{
    return ++incrementable;
}

Answer 7

Change your inner loop to this:

if(outter->second.size()) {
    inner = outter->second.begin();
    while(true) {
        cout<<inner->first<<","<<inner->second;
        if(++inner != outer->second.end()) {
            cout<<",";
        } else {
            break;
        }
    }
}