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std::tuple::tuple

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< cpp‎ | utility‎ | tuple
Revision as of 05:10, 24 August 2013 by Cubbi (Talk | contribs)

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Defined in header <tuple>
constexpr tuple();
(1) (since C++11)
explicit tuple( const Types&... args );
(2) (since C++11)
(until C++14)
explicit constexpr tuple( const Types&... args );
(2) (since C++14)
template< class... UTypes >
explicit tuple( UTypes&&... args );
(3) (since C++11)
(until C++14)
template< class... UTypes >
explicit constexpr tuple( UTypes&&... args );
(3) (since C++14)
template< class... UTypes >
tuple( const tuple<UTypes...>& other );
(4) (since C++11)
(until C++14)
template< class... UTypes >
constexpr tuple( const tuple<UTypes...>& other );
(4) (since C++14)
template <class... UTypes>
tuple( tuple<UTypes...>&& other );
(5) (since C++11)
(until C++14)
template <class... UTypes>
constexpr tuple( tuple<UTypes...>&& other );
(5) (since C++14)
template< class U1, class U2 >
tuple( const pair<U1,U2>& p );
(6) (since C++11)
(until C++14)
template< class U1, class U2 >
constexpr tuple( const pair<U1,U2>& p );
(6) (since C++14)
template< class U1, class U2 >
tuple( pair<U1,U2>&& p );
(7) (since C++11)
(until C++14)
template< class U1, class U2 >
constexpr tuple( pair<U1,U2>&& p );
(7) (since C++14)
tuple( const tuple& other ) = default;
(8) (since C++11)
tuple( tuple&& other ) = default;
(9) (since C++11)
template< class Alloc >
tuple( std::allocator_arg_t, const Alloc& a );
(10) (since C++11)
template< class Alloc >
tuple( std::allocator_arg_t, const Alloc& a, const Types&... args );
(11) (since C++11)
template< class Alloc, class... UTypes >
tuple( std::allocator_arg_t, const Alloc& a, UTypes&&... args );
(12) (since C++11)
template <class Alloc, class... UTypes>
tuple( std::allocator_arg_t, const Alloc& a, const tuple<UTypes...>& other );
(13) (since C++11)
template< class Alloc, class... UTypes >
tuple( std::allocator_arg_t, const Alloc& a, tuple<UTypes...>&& other );
(14) (since C++11)
template< class Alloc, class U1, class U2 >
tuple( std::allocator_arg_t, const Alloc& a, const pair<U1, U2>& p );
(15) (since C++11)
template< class Alloc, class U1, class U2 >
tuple( std::allocator_arg_t, const Alloc& a, pair<U1, U2>&& p );
(16) (since C++11)
template< class Alloc >
tuple( std::allocator_arg_t, const Alloc& a, const tuple& other );
(17) (since C++11)
template< class Alloc >
tuple( std::allocator_arg_t, const Alloc& a, tuple&& other );
(18) (since C++11)

Constructs a new tuple.

1) Default constructor. Value-initializes all elements.

2) Initializes each element of the tuple with the corresponding parameter.

3) Initializes each element of the tuple with the corresponding value in std::forward<Utypes>(args).

4) For all i in sizeof...(UTypes), initializes ith element of the tuple with std::get<i>(other).

5) For all i in sizeof...(UTypes), initializes ith element of the tuple with std::forward<Ui>(std::get<i>(other)).

6) Constructs a 2-element tuple with the first element constructed from p.first and the second element from p.second

7) Constructs a 2-element tuple with the first element constructed from std::forward<U1>(p.first) and the second element from std::forward<U2>(p.second)

8) Compiler-generated copy constructor. Initializes each element of the tuple with the corresponding element of other. This constructor is constexpr if every operation it performs is constexpr. For the empty tuple std::tuple<>, it is constexpr.

9) Compiler-generated move constructor. Initializes each ith element of the tuple with std::forward<Ui>(std::get<i>(other)). This constructor is constexpr if every operation it performs is constexpr. For the empty tuple std::tuple<>, it is constexpr.

10 - 18) Identical to 1-9 except each element is created by uses-allocator construction, that is, the Allocator object a is passed as an additional argument to the constructor of each element for which std::uses_allocator<Ui, Alloc>::value is true.

[edit] Parameters

args - values used to initialize each element of the tuple
other - a tuple of values used to initialize each element of the tupe
p - pair of values used to initialize both elements of this 2-tuple
a - allocator to use in uses-allocator construction

[edit] Example

#include <iostream>
#include <string>
#include <vector>
#include <tuple>
#include <memory>
 
// helper function to print a tuple of any size
template<class Tuple, std::size_t N>
struct TuplePrinter {
    static void print(const Tuple& t) 
    {
        TuplePrinter<Tuple, N-1>::print(t);
        std::cout << ", " << std::get<N-1>(t);
    }
};
 
template<class Tuple>
struct TuplePrinter<Tuple, 1>{
    static void print(const Tuple& t) 
    {
        std::cout << std::get<0>(t);
    }
};
 
template<class... Args>
void print(const std::tuple<Args...>& t) 
{
    std::cout << "(";
    TuplePrinter<decltype(t), sizeof...(Args)>::print(t);
    std::cout << ")\n";
}
// end helper function
 
int main()
{
    std::tuple<int, std::string, double> t1;
    std::cout << "Value-initialized: "; print(t1);
    std::tuple<int, std::string, double> t2(42, "Test", -3.14);
    std::cout << "Initialized with values: "; print(t2);
    std::tuple<char, std::string, int> t3(t2);
    std::cout << "Implicitly converted: "; print(t3);
    std::tuple<int, double> t4(std::make_pair(42, 3.14));
    std::cout << "Constructed from a pair"; print(t4);
 
    // given Allocator my_alloc with a single-argument constructor my_alloc(int)
    // use my_alloc(1) to allocate 10 ints in a vector
    std::vector<int, my_alloc> v(10, 1, my_alloc(1));
    // use my_alloc(2) to allocate 10 ints in a vector in a tuple
    std::tuple<int, std::vector<int, my_alloc>, double> t5(std::allocator_arg,
                                                           my_alloc(2), 42, v,  -3.14);
}

Output:

Value-initialized: (0, , 0)
Initialized with values: (42, Test, -3.14)
Implicitly converted: (*, Test, -3)
Constructed from a pair(42, 3.14)

[edit] See also

creates a tuple object of the type defined by the argument types
(function template) [edit]
creates a tuple of lvalue references or unpacks a tuple into individual objects
(function template) [edit]
creates a tuple of rvalue references
(function template) [edit]