How to find whether an element exists in std::map?

Question

My use case:

map<string, Car> cars;
bool exists(const string& name) {
  // somehow I should find whether my MAP has a car
  // with the name provided
  return false;
} 

Could you please suggest the best and the most elegant way to do it in C++? Thanks.

Answer 1

bool exists(const string& name)
{
    return cars.find(name) != cars.end();
}

Answer 2

return cars.find(name) != cars.end();

Answer 3

Sure, use an iterator

map<string,Car>::const_iterator it = cars.find(name);
return it!=cars.end();

Answer 4

bool exists(const std::map<std::string, Car>& cars, const std::string& name) {
  return cars.end() != cars.find(name);
}

Answer 5

std::map::find(const key_type& x );

It returns map::end if the item doesn't exist.

Answer 6

You could also use

bool exists(const string& name) {
  return cars.count(name) != 0;
} 

Answer 7

What about:

template <typename KeyType, typename Collection>
bool exists_in(Collection const& haystack, KeyType const& needle) {
    return std::find(haystack.begin(), haystack.end(), needle) != haystack.end();
}

template <typename K, typename V>
bool exists_in(std::map<K,V> const& haystack, K const& needle) {
    return haystack.find(needle) != haystack.end();
}

This makes exists_in work with any standard container via std::find and use a special version for std::map since it offers a more efficient searching alternative. You could add additional specializations as necessary (e.g., for std::set and others).