Std::hash

Disabled specializations do not satisfy Hashdo not satisfy FunctionObjectand following values are all std::hash :.

The hash template defines a function object that implements a hash function. Instances of this function object define an operator that:. The hash template is both CopyConstructible and Destructible. The actual hash functions are implementation-dependent and are not required to fulfill any other quality criteria except those specified above. Notably, some implementations use trivial identity hash functions which map an integer to itself.

Std::hash

The hash class is default constructible, which means that one can construct this object without any arguments or initialization values. It is used to get the hash value of the argument that is being passed to it. Member functions: This Hash class only has one member function:. Skip to content. Change Language. Open In App. Related Articles. Solve Coding Problems. Improve Improve. Like Article Like. Save Article Save. Report issue Report. Output: String hash values: Bitset hash value: Vector hash value: Char hash values:

Notably, std::hash, some implementations use trivial identity hash functions which map an integer to std::hash. Work Experiences. Trait std :: hash :: Hash 1.

The hash template defines a function object that implements a hash function. Instances of this function object satisfy Hash. In particular, they define an operator that:. The hash template is both CopyConstructible and Destructible. The actual hash functions are implementation-dependent and are not required to fulfill any other quality criteria except those specified above.

Disabled specializations do not satisfy Hash , do not satisfy FunctionObject , and following values are all false :. Each header that declares the template std::hash also provides enabled specializations of std::hash for the following types:. On top of that, some headers also provide other enabled std::hash specializations for library types see below. For all std::hash specializations provided by the standard library except the following, all their member functions are noexcept :. The actual hash functions are implementation-dependent and are not required to fulfill any other quality criteria except those specified above. Notably, some implementations use trivial identity hash functions which map an integer to itself. In other words, these hash functions are designed to work with unordered associative containers, but not as cryptographic hashes, for example.

Std::hash

Each specialization of this template is either enabled "untainted" or disabled "poisoned". In other words, they exist, but cannot be used. Instances of this function object satisfy Hash. In particular, they define an operator const that:. All explicit and partial specializations of hash provided by the standard library are DefaultConstructible , CopyAssignable , Swappable and Destructible. User-provided specializations of hash also must meet those requirements. The actual hash functions are implementation-dependent and are not required to fulfill any other quality criteria except those specified above.

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Contents 1 Notes 2 Member types 3 Member functions 4 Standard specializations for basic types 5 Standard specializations for library types 6 Examples. The resulting hash will be the combination of the values from calling hash on each field. Add Other Experiences. Report issue Report. Related Articles. Run this code. Trait std :: hash :: Hash 1. Share your suggestions to enhance the article. Integer comparison functions. Improved By :. Article Tags :.

Each specialization of this template is either enabled "untainted" or disabled "poisoned". In other words, they exist, but cannot be used. Instances of this function object satisfy Hash.

Please Login to comment This means that unsafe code must not rely on the correctness of these methods. Disabled specializations do not satisfy Hash , do not satisfy FunctionObject , and following values are all false :. Create Improvement. Instances of this function object satisfy Hash. The hash template is both CopyConstructible and Destructible. HashMap and HashSet both rely on this behavior. Engineering Exam Experiences. The hash template defines a function object that implements a hash function. Contents 1 Nested types 2 Member functions 3 Standard library specializations 4 Specializations for library types 5 Notes 6 Example 7 Defect reports. Swap and type operations.