std::make_pair
Defined in header <utility>
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template
<
class T1, class T2 >
std::pair <T1, T2> make_pair( T1 x, T2 y ) ; |
(until C++11) | |
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template
<
class T1, class T2 >
std::pair < /*V1*/, /*V2*/ > make_pair( T1&& x, T2&& y ) ; |
(since C++11) (constexpr since C++14) (until C++20) |
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template
<
class T1, class T2 >
constexpr
std::pair
<
std::unwrap_ref_decay_t
<T1>, |
(since C++20) | |
Creates a std::pair object, deducing the target type from the types of arguments.
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Given types
std::decay
<T1>
::
type
as
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(since C++11) (until C++20) |
Parameters
| x, y | - | the values to construct the pair from |
Return value
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std::pair <T1, T2> (x, y) |
(until C++11) |
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std::pair < /*V1*/, /*V2*/ > ( std::forward <T1> (x), std::forward <T2> (y) ) |
(since C++11) (until C++20) |
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std::pair
<
std::unwrap_ref_decay_t
<T1>, std::unwrap_ref_decay_t
<T2>>
|
(since C++20) |
Example
#include <functional> #include <iostream> #include <utility> int main() { int n = 1; int a[5] = {1, 2, 3, 4, 5}; // build a pair from two ints auto p1 = std::make_pair(n, a[1]); std::cout << "The value of p1 is " << '(' << p1.first << ", " << p1.second << ")\n"; // build a pair from a reference to int and an array (decayed to pointer) auto p2 = std::make_pair(std::ref(n), a); n = 7; std::cout << "The value of p2 is " << '(' << p2.first << ", " << *(p2.second + 2) << ")\n"; }
Output:
The value of p1 is (1, 2) The value of p2 is (7, 3)
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 181 | C++98 | the parameter types were const-reference types, which made passing arrays impossible |
changed these types to value types |