Question

I had trouble searching for potential duplicates because I’m not sure what the correct terminology is.

If I have many vectors which are already created, how can I loop through them? To make things simple, suppose I have three vectors of strings named "vec_one", "vec_two", "vec_three".

I want to do something like:

for i in ("vec_one", "vec_two", "vec_three") {
    for (vector<string>::const_iterator iter = i.begin(); iter != i.end(); ++iter) {
        //do something with the elements ***and I need to access "i"***, that is, the vector name.
    }
}

This would be the same as writing three different for loops, but would be more readable and in fact I have more than three in my non-simple application.

Note that because I need to access the vector name (see the comment), I can’t just merge them all together and then run one loop.

Answer 1

You could put the the vectors in a vector<std::pair<std::string, std::vector<...>*>:

std::vector<std::pair<std::string, std::vector<std::string>*> > vectors;
vectors.emplace_back(std::string("vec_one"), &vec_one); //or push_back(std::make_pair(...)) in C++03
vectors.emplace_back(std::string("vec_two"), &vec_two); 
vectors.emplace_back(std::string("vec_three"), &vec_three); 
for(auto iter = vectors.begin(); iter != vectors.end(); ++iter)//used c++11 auto here for brevity, but that isn't necessary if C++11 is not availible
    for(auto vecIter = iter->second->begin(); vecIter != iter->second->end(); ++vecIter)
    //get name with iter->first, body here

That way you can get the name easily from the outer iterator.

If you use C++11 you can use std::array instead:

std::array<std::pair<std::string, std::vector<std::string>*>, 3> vectors =
{
    std::make_pair(std::string("vec_one"), &vec_one),
    std::make_pair(std::string("vec_two"), &vec_two),
    std::make_pair(std::string("vec_three"), &vec_three)
};

In C++03 you could use buildin arrays instead, but unless the extra overhead for the vector is a problem for you (unlikely) I don’t see a compelling reason to do so. boost::array is also a noteworthy alternative if you can’t use C++11

If you do need the absolute optimal performance it might be worthwile to directly use const char* instead of std::string for the names.