Question

Q: How would I determine if a "key" exists in a map?

Context: Im making an image manager that has a single function that takes a string paramater that is the file folder/file name of the image file.

Example: Image& Ret(string FileName)

I want it to return a reference to the image that has been stored in memory. The function will have a dual purpose of being a "setter" and "getter." The map is so the keys will be the FileName. How would I go about determining if map[FileName] exists? I tried using find() but it returns an iterator and I tried evaluating it as NULL but it didnt work, so im kind of lost as to how I would check it or if there is a better way.

Thank you! :)

Answer 1

You need to simply check if the iterator returned is == the end of the map. If it is, then the key wasn't found.

if (map.find("key") == map.end() )
{
    // Didn't Find it
}

Answer 2

Do you mean this?

struct Image
{
    Image(int a) : a(a) {}
    int a;
};

int main()
{
    map<string, Image> images;
    images.insert(make_pair("Five", Image(5)));
    images.insert(make_pair("Ten", Image(10)));
    cout << images.find("Five")->second.a << endl;
}