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std::set find() method

// (1) Const version
size_type count( const Key& key ) const;

// (2) Const version
template< class K >
size_type count( const K& x ) const;
  • (1-2) Finds an element with key equivalent to key.
  • (3-4) Finds an element with key that compares equivalent to the value x. This overload participates in overload resolution only if the qualified-id Compare::is_transparent is valid and denotes a type. It allows calling this function without constructing an instance of Key.

Parameters

  • key - key value of the elements to count
  • x - a value of any type that can be transparently compared with a key

Return value

Iterator to an element with key equivalent to key. If no such element is found, past-the-end (see end()) iterator is returned.

Complexity

Logarithmic in the size of the container - O(log size()).

Exceptions

(none)

Notes

Feature testing macro: __cpp_lib_generic_unordered_lookup (for overload (3-4)).

Example

Main.cpp
#include <iostream>
#include <set>

struct FatKey { int x; int data[1000]; };
struct LightKey { int x; };
// Note: as detailed above, the container must use std::less<> (or other
// transparent Comparator) to access these overloads.
// This includes standard overloads, such as between std::string and std::string_view.
bool operator<(const FatKey& fk, const LightKey& lk) { return fk.x < lk.x; }
bool operator<(const LightKey& lk, const FatKey& fk) { return lk.x < fk.x; }
bool operator<(const FatKey& fk1, const FatKey& fk2) { return fk1.x < fk2.x; }

int main()
{
// simple comparison demo
std::set<int> example = {1, 2, 3, 4};

auto search = example.find(2);
if (search != example.end()) {
std::cout << "Found " << (*search) << '\n';
} else {
std::cout << "Not found\n";
}

// transparent comparison demo
std::set<FatKey, std::less<>> example2 = { {1, {} }, {2, {} }, {3, {} }, {4, {} } };

LightKey lk = {2};
auto search2 = example2.find(lk);
if (search2 != example2.end()) {
std::cout << "Found " << search2->x << '\n';
} else {
std::cout << "Not found\n";
}

}
Possible output
Found 2
Found 2
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.

std::set find() method

// (1) Const version
size_type count( const Key& key ) const;

// (2) Const version
template< class K >
size_type count( const K& x ) const;
  • (1-2) Finds an element with key equivalent to key.
  • (3-4) Finds an element with key that compares equivalent to the value x. This overload participates in overload resolution only if the qualified-id Compare::is_transparent is valid and denotes a type. It allows calling this function without constructing an instance of Key.

Parameters

  • key - key value of the elements to count
  • x - a value of any type that can be transparently compared with a key

Return value

Iterator to an element with key equivalent to key. If no such element is found, past-the-end (see end()) iterator is returned.

Complexity

Logarithmic in the size of the container - O(log size()).

Exceptions

(none)

Notes

Feature testing macro: __cpp_lib_generic_unordered_lookup (for overload (3-4)).

Example

Main.cpp
#include <iostream>
#include <set>

struct FatKey { int x; int data[1000]; };
struct LightKey { int x; };
// Note: as detailed above, the container must use std::less<> (or other
// transparent Comparator) to access these overloads.
// This includes standard overloads, such as between std::string and std::string_view.
bool operator<(const FatKey& fk, const LightKey& lk) { return fk.x < lk.x; }
bool operator<(const LightKey& lk, const FatKey& fk) { return lk.x < fk.x; }
bool operator<(const FatKey& fk1, const FatKey& fk2) { return fk1.x < fk2.x; }

int main()
{
// simple comparison demo
std::set<int> example = {1, 2, 3, 4};

auto search = example.find(2);
if (search != example.end()) {
std::cout << "Found " << (*search) << '\n';
} else {
std::cout << "Not found\n";
}

// transparent comparison demo
std::set<FatKey, std::less<>> example2 = { {1, {} }, {2, {} }, {3, {} }, {4, {} } };

LightKey lk = {2};
auto search2 = example2.find(lk);
if (search2 != example2.end()) {
std::cout << "Found " << search2->x << '\n';
} else {
std::cout << "Not found\n";
}

}
Possible output
Found 2
Found 2
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.