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Example shown above demonstrates the usage of some of the functions provided by map, such as insert() (place element into the map), erase() (remove element from the map), find() (check presence of the element in the container), etc.
The Standard Template Library (STL) is a software library originally designed by Alexander Stepanov for the C++ programming language that influenced many parts of the C++ Standard Library. It provides four components called algorithms , containers , functions , and iterators .
To use custom objects in std::unordered_map, a custom hash function must be defined. This function takes a const reference to the custom type and returns a size_t #include <unordered_map> struct X { int i , j , k ;}; struct hash_X { size_t operator ()( const X & x ) const { return std :: hash < int > ()( x . i ) ^ std :: hash < int > ()( x . j ...
Although std::map is typically implemented using a self-balancing binary search tree, C++11 defines a second map called std::unordered_map, which has the algorithmic characteristics of a hash table. This is a common vendor extension to the Standard Template Library (STL) as well, usually called hash_map , available from such implementations as ...
The C++ Standard Library is based upon conventions introduced by the Standard Template Library (STL), and has been influenced by research in generic programming and developers of the STL such as Alexander Stepanov and Meng Lee. [4] [5] Although the C++ Standard Library and the STL share many features, neither is a strict superset of the other.
Lookup, find, or get find the value (if any) that is bound to a given key. The argument to this operation is the key, and the value is returned from the operation. If no value is found, some lookup functions raise an exception, while others return a default value (such as zero, null, or a specific value passed to the constructor).
In Haskell, the polymorphic function map :: (a -> b) -> [a] -> [b] is generalized to a polytypic function fmap :: Functor f => (a -> b) -> f a -> f b, which applies to any type belonging the Functor type class. The type constructor of lists [] can be defined as an instance of the Functor type class using the map function from the previous example:
Since C++20, using auto or Concept auto in any of the parameters of a function declaration, that declaration becomes an abbreviated function template declaration. [4] Such a declaration declares a function template and one invented template parameter for each placeholder is appended to the template parameter list: