Question

I’m using a map to store a bunch of keys and values. I want to use find() to find the key and return the value. Unfortunately, when I can’t find the key, it get’s upset. How can I make it return 0 if no key is found?

 int bag::getItem( const string item)
 {
    return this->bagItems.find(item)->second;
    return 0;
 }

Any suggestions would be greatly appreciated.

Answer 1

map::find returns the value of map::end() if the value was not found. That’s an iterator value that you cannot dereference, so blindly doing bagItems.find(item)->second is a no-no.

Instead, check the return value and act accordingly:

int bag::getItem( const string item) 
{ 
    // We don't know what CONST_ITERATOR_TYPE is, but you do
    CONST_ITERATOR_TYPE i = this->bagItems.find(item);
    return i == this->bagItems.end() ? 0 : i->second;
} 

To do this, you ‘ll want to have a local variable of const_iterator type; however, that type depends on the template arguments of your map (which we don’t know). So you will have to fill the blank in yourself.

If you are in the pleasant position of using a C++11 compiler, the convenient

auto i = this->bagItems.find(item);

will work.