tuple元组（C++11及以后，如C++14）

类tuple与array最本质的区别当数tuple元组元素类型可以不一样，而统一数组array的元素类型必须一样。

本文主要举例：

tuple_size

Example

// tuple example
#include <iostream>     // std::cout
#include <tuple>        // std::tuple, std::get, std::tie, std::ignore

int main ()
{
  std::tuple<int,char> foo (10,'x');
  auto bar = std::make_tuple ("test", 3.1, 14, 'y');

  std::get<2>(bar) = 100;                                    // access element and change its value

  int myint; char mychar;

  std::tie (myint, mychar) = foo;                            // unpack elements
  std::tie (std::ignore, std::ignore, myint, mychar) = bar;  // unpack (with ignore)

  mychar = std::get<3>(bar);

  std::get<0>(foo) = std::get<2>(bar);
  std::get<1>(foo) = mychar;

  std::cout << "foo contains: ";
  std::cout << std::get<0>(foo) << ' ';
  std::cout << std::get<1>(foo) << '\n';

  return 0;
}

Edit & Run

Output:

foo contains: 100 y

tie----（unpack）

Example

// packing/unpacking tuples
#include <iostream>     // std::cout
#include <tuple>        // std::tuple, std::make_tuple, std::tie

int main ()
{
  int myint;
  char mychar;

  std::tuple<int,float,char> mytuple;

  mytuple = std::make_tuple (10, 2.6, 'a');          // packing values into tuple

  std::tie (myint, std::ignore, mychar) = mytuple;   // unpacking tuple into variables

  std::cout << "myint contains: " << myint << '\n';
  std::cout << "mychar contains: " << mychar << '\n';

  return 0;
}

Edit & Run

Output:

myint contains: 10
mychar contains: a

std:tuple_element

Member types

member type	definition
`type`	The `I`th type in the `tuple` object

Example

// tuple_element
#include <iostream>     // std::cout
#include <tuple>        // std::tuple, std::make_tuple, std::tuple_element, std::get

int main ()
{
  auto mytuple = std::make_tuple (10,'a');

  std::tuple_element<0,decltype(mytuple)>::type first = std::get<0>(mytuple);
  std::tuple_element<1,decltype(mytuple)>::type second = std::get<1>(mytuple);

  std::cout << "mytuple contains: " << first << " and " << second << '\n';

  return 0;
}

Edit & Run

Output:

mytuple contains: 10 and a

tuple_size

Member constants

member constant	definition
`value`	The number of elements in the `tuple` or tuple-like object. This is a `constexpr` value of the unsigned integral type `size_t`.

Example

// tuple_size
#include <iostream>     // std::cout
#include <tuple>        // std::tuple, std::tuple_size

int main ()
{
  std::tuple<int,char,double> mytuple (10,'a',3.14);

  std::cout << "mytuple has ";
  std::cout << std::tuple_size<decltype(mytuple)>::value;
  std::cout << " elements." << '\n';

  return 0;
}

Edit & Run

Output:

mytuple has 3 elements

forward_as_tuple

Parameters

args: List of elements to be forwarded as a tuple object of references.

Return Value

A tuple object with rvalue references to args suitable to be forwarded as argument to a function.

Example

// forward_as_tuple example
#include <iostream>     // std::cout
#include <tuple>        // std::tuple, std::get, std::forward_as_tuple
#include <string>       // std::string

void print_pack (std::tuple<std::string&&,int&&> pack) {
  std::cout << std::get<0>(pack) << ", " << std::get<1>(pack) << '\n';
}

int main() {
  std::string str ("John");
  print_pack (std::forward_as_tuple(str+" Smith",25));
  print_pack (std::forward_as_tuple(str+" Daniels",22));
  return 0;
}

Edit & Run

Output:

John Smith, 25
John Daniels, 22

tuple_cat

Parameters

tpls: Comma-separated list of tuple objects. These may be of different types.

Return Value

A tuple object of the appropriate type to hold args.

The type of the returned object (tuple<CTypes...>) is the tuple type that contains the ordered sequence of all the extended types inTuples.

Example

// tuple_cat example
#include <iostream>     // std::cout
#include <utility>      // std::pair
#include <string>       // std::string
#include <tuple>        // std::tuple, std::tuple_cat, std::get

int main ()
{

  std::tuple<float,std::string> mytuple (3.14,"pi");
  std::pair<int,char> mypair (10,'a');

  auto myauto = std::tuple_cat ( mytuple, std::tuple<int,char>(mypair) );

  std::cout << "myauto contains: " << '\n';
  std::cout << std::get<0>(myauto) << '\n';
  std::cout << std::get<1>(myauto) << '\n';
  std::cout << std::get<2>(myauto) << '\n';
  std::cout << std::get<3>(myauto) << '\n';

  return 0;
}

Edit & Run

Output:

myauto contains:
3.14
pi
10
a

ignore tie

Parameters

args: List of objects (lvalues) to be tied as elements of a tuple.

Return Value

A tuple with lvalue references to args.

Example

// packing/unpacking tuples
#include <iostream>     // std::cout
#include <tuple>        // std::tuple, std::make_tuple, std::tie

int main ()
{
  int myint;
  char mychar;

  std::tuple<int,float,char> mytuple;

  mytuple = std::make_tuple (10, 2.6, 'a');          // packing values into tuple

  std::tie (myint, std::ignore, mychar) = mytuple;   // unpacking tuple into variables

  std::cout << "myint contains: " << myint << '\n';
  std::cout << "mychar contains: " << mychar << '\n';

  return 0;
}