std::map<keyT, valueT> foo; // ...
keyT key; // ...

std::map<keyT, valueT>::const_iterator item = foo.find(key);

if(item != foo.end()) {
    // The iterator is valid, so we can dereference the pointed item directly.
    const std::pair<keyT, valueT>& real_item = *item;
    // And do something with it.
} else {
    // The iterator is not valid, so that means there's no element whose key is 'key'
    // in the 'foo' container.
}