在这个示例中,程序会输出“Key exists in the map with value: 10”,因为键“banana”存在于unordered_map中。如果你将keyToCheck更改为一个不存在的键,如“date”,程序将输出“Key does not exist in the map”。
相反，我更愿意使用std::unordered_map::find。因此，如果您确定第一个键存在，但第二个键不存在，您...
1template <class_Key,class_Tp,class_Hash = hash<_Key>,class_Pred = equal_to<_Key>,2class_Alloc = allocator<pair<const_Key, _Tp> > >3class_LIBCPP_TEMPLATE_VIS unordered_map4{5public:6//types7typedef _Key key_type;8typedef _Tp mapped_type;9typedef _Hash hasher;10typedef _Pred key...
10)Ifnhis an emptynode handle, does nothing and returns the end iterator. Otherwise, inserts the element owned bynhinto the container, if the container doesn't already contain an element with a key equivalent tonh.key(), and returns the iterator pointing to the element with key equivalent ...
key,因此您可以简单地使用 unordered_map::find方法来检查它是否存在: void addEmployee(std::string_view newName, int newTime) { // first check if they name already exists, if it does then do nothing and return auto it = myDictionary.find(newName); if (it != myDictionary.end()) { std...
When accessing with [], if the key does not exist, the map will insert a new element with the default value. When accessing with at(), if the key does not exist, an exception will be thrown. Using find() allows you to check if the key exists without modifying the map. ...
containsC++20 Check if there's an element with the specified key in the unordered_map. emplace Adds an element constructed in place. emplace_hint Adds an element constructed in place, with hint. empty Tests whether no elements are present. end Designates the end of the controlled sequence. eq...
The first element has the key 50, which is not the same as the 256 we are looking for, so the map will continue to iterate. The next element has the key 256, which is exactly the one we need. The corresponding value is xyz. If the key weren't in the dictionary, the map would ...
containsC++20 Check if there's an element with the specified key in the unordered_map. emplace Adds an element constructed in place. emplace_hint Adds an element constructed in place, with hint. empty Tests whether no elements are present. end Designates the end of the controlled sequence. eq...
key(). The behavior is undefined if nh is not empty and get_allocator() != nh.get_allocator().8) If nh is an empty node handle, does nothing and returns the end iterator. Otherwise, inserts the element owned by nh into the container, if the container doesn't already contain an ...