即使我分配了一个值，std :: map的值还是空的？

Question

I have a std::map like this :

std::map<std::string, std::string> imagePaths;

Later in my code I give it one value, like this :

imagePaths.insert(std::make_pair("Square.bmp", "Square"));

However, when I loop trough the map and display both first and second values like this :

for (auto iterator = imagePaths.begin(); iterator != imagePaths.end(); iterator++)
{
    std::cout << "Loaded > " << imagePaths[iterator->first] << " image path : " << imagePaths[iterator->second] << std::endl;
}

I get the output :

Loaded > Square image path :

And the rest is, for some reason empty, even though I gave it a value of "Square.bmp" .

---

Can't figure out what I'm doing wrong. :/

Answer 1

You are using the wrong way to display a map content.

Try this:

for (auto iterator = imagePaths.begin(); iterator != imagePaths.end(); iterator++)
{
   std::cout << "Loaded > " << iterator->first << " image path : " << iterator->second << std::endl;
}

To lookup a value using the key you use .find() method. In your case, if you execute this statement:

std::map<std::string, std::string>::const_iterator i = imagePaths.find("Square.bmp");

std::string value = it->second;

value will be "Square".

Answer 2

The std::map maps the first element of the pair to the second, it does not work the other way round.

Aside from that, it does not make sense to apply the mapping in your loop at all because you already can access both values via the iterator.