std::tuple_cat

 

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std::tuple

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tuple::tuple

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make_tuple

tie

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tuple_cat

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Defined in header <tuple>
template< class... Tuples > std::tuple<CTypes...> tuple_cat( Tuples&&... args );		(since C++11) (until C++14)
template< class... Tuples > constexpr std::tuple<CTypes...> tuple_cat( Tuples&&... args );		(since C++14) (until C++23)
template< /*tuple-like*/... Tuples > constexpr std::tuple<CTypes...> tuple_cat( Tuples&&... args );		(since C++23)

Constructs a tuple that is a concatenation of all tuples in args.

The behavior is undefined if any type in std::decay_t<Tuples>... is not a specialization of std::tuple. However, an implementation may choose to support types (such as std::array and std::pair) that follow the tuple-like protocol.	(until C++23)
The types std::decay_t<Tuples>... are constrained to be tuple-like, i.e. each type therein is required to be a specialization of std::tuple or another type (such as std::array and std::pair) that models the tuple-like concept.	(since C++23)

Parameters

args

-

zero or more tuples to concatenate

Return value

A std::tuple object composed of all elements of all argument tuples constructed from std::get<j>(std::forward<Ti>(arg)) for each individual element.

Example

Run this code

#include <iostream>
#include <tuple>
#include <string>
 
// 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 <typename... Args, std::enable_if_t<sizeof...(Args) == 0, int> = 0>
void print(const std::tuple<Args...>& t)
{
    std::cout << "()\n";
}
 
template <typename... Args, std::enable_if_t<sizeof...(Args) != 0, int> = 0>
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, float> t1(10, "Test", 3.14);
    int n = 7;
    auto t2 = std::tuple_cat(t1, std::make_tuple("Foo", "bar"), t1, std::tie(n));
    n = 42;
    print(t2);
}

Output:

(10, Test, 3.14, Foo, bar, 10, Test, 3.14, 42)

See also

make_tuple (C++11)	creates a tuple object of the type defined by the argument types (function template)
tie (C++11)	creates a tuple of lvalue references or unpacks a tuple into individual objects (function template)
forward_as_tuple (C++11)	creates a tuple of forwarding references (function template)