how to properly iterate over a container

[Dy7SLyTq]

so i have a container called Source that is of type std::map<std::string, std::vector<std::string>> but when I try to print it with this function:

void Lexer::PrintSource()
{
    for(auto Iterator = this->Source.begin(); Iterator != this->Source.end(); Iterator++)
        for(auto SubIterator = Iterator->begin(); SubIterator != Iterator->end(); SubIterator++)
            cout<< *SubIterator << endl;
}

i get these errors:

Lexer.cpp: In member function 'void Lexer::PrintSource()':
Lexer.cpp:29:42: error: 'struct std::pair<const std::basic_string<char>, std::vector<std::basic_string<char> > >' has no member named 'begin'
         for(auto SubIterator = Iterator->begin(); SubIterator != Iterator->end(); SubIterator++)
                                          ^
Lexer.cpp:29:76: error: 'struct std::pair<const std::basic_string<char>, std::vector<std::basic_string<char> > >' has no member named 'end'
         for(auto SubIterator = Iterator->begin(); SubIterator != Iterator->end(); SubIterator++)
                                                                            ^

[Disch]

'Iterator' is a iterator to a map. Which means *Iterator is a pair<string,vector<blah>>.

If you want to iterate over the vector:

    for(auto Iterator = this->Source.begin(); Iterator != this->Source.end(); ++Iterator) // favor prefix form of ++
        for(auto SubIterator = Iterator->second.begin(); SubIterator != Iterator->second.end(); ++SubIterator)
            cout<< *SubIterator << endl;

Or... more simply:

for(auto& i : Source)
    for(auto& sub : i.second)
        cout << sub << endl;

[Dy7SLyTq]

thank you that worked

[Dy7SLyTq]

one more question:
is it possible to convert an iterator to int to find out how many times it has iterated through the container?

[Disch]

For most containers... no. Having that ability would mean the container would have to be indexed.

For random access containers (like vector), however... yes:

int index = myiter - myvector.begin();

[JLBorges]

> is it possible to convert an iterator to int to find out how many times it has iterated through the container?

Obviously yes. It is the number of times std::begin(cntr) would have to be incremented before it becomes equal to the iterator.

auto pos = std::distance( some_iter, std::begin(cntr) ) ;
http://en.cppreference.com/w/cpp/iterator/distance

O(1) if the iterator is a RandomAccessIterator, linear otherwise.

[Disch]

Whooop forgot about std::distance.

Though just note, as you mentioned it's linear complexity for non-random access containers so it's less "conversion" and more "iterating over the container again".