std::tuple
std::tuple
| Defined in header | | |
|---|---|---|
| template< class... Types > class tuple; | | (since C++11) |
Class template std::tuple is a fixed-size collection of heterogeneous values. It is a generalization of std::pair.
| If (std::is_trivially_destructible_v | (since C++17) |
|---|
Template parameters
| Types... | - | the types of the elements that the tuple stores. Empty list is supported. |
|---|
Member functions
| (constructor) | constructs a new tuple (public member function) |
|---|---|
| operator= | assigns the contents of one tuple to another (public member function) |
| swap | swaps the contents of two tuples (public member function) |
Non-member functions
| make_tuple | creates a tuple object of the type defined by the argument types (function template) |
|---|---|
| tie | creates a tuple of lvalue references or unpacks a tuple into individual objects (function template) |
| forward_as_tuple | creates a tuple of rvalue references (function template) |
| tuple_cat | creates a tuple by concatenating any number of tuples (function template) |
| std::get(std::tuple) | tuple accesses specified element (function template) |
| operator==operator!=operator<operator<=operator>operator>= | lexicographically compares the values in the tuple (function template) |
| std::swap(std::tuple) (C++11) | specializes the std::swap algorithm (function template) |
Helper classes
| tuple_size | obtains the size of tuple at compile time (class template specialization) |
|---|---|
| tuple_element | obtains the type of the specified element (class template specialization) |
| std::uses_allocator<std::tuple> (C++11) | specializes the std::uses_allocator type trait (class template specialization) |
| ignore | placeholder to skip an element when unpacking a tuple using tie (constant) |
Notes
Until C++17, a function could not return a tuple using list-initialization:
std::tuple<int, int> foo_tuple()
{
return {1, -1}; // Error until C++17
return std::make_tuple(1, -1 // Always works
}
Example
#include <tuple>
#include <iostream>
#include <string>
#include <stdexcept>
std::tuple<double, char, std::string> get_student(int id)
{
if (id == 0) return std::make_tuple(3.8, 'A', "Lisa Simpson"
if (id == 1) return std::make_tuple(2.9, 'C', "Milhouse Van Houten"
if (id == 2) return std::make_tuple(1.7, 'D', "Ralph Wiggum"
throw std::invalid_argument("id"
}
int main()
{
auto student0 = get_student(0
std::cout << "ID: 0, "
<< "GPA: " << std::get<0>(student0) << ", "
<< "grade: " << std::get<1>(student0) << ", "
<< "name: " << std::get<2>(student0) << '\n';
double gpa1;
char grade1;
std::string name1;
std::tie(gpa1, grade1, name1) = get_student(1
std::cout << "ID: 1, "
<< "GPA: " << gpa1 << ", "
<< "grade: " << grade1 << ", "
<< "name: " << name1 << '\n';
}
Output:
ID: 0, GPA: 3.8, grade: A, name: Lisa Simpson
ID: 1, GPA: 2.9, grade: C, name: Milhouse Van Houten
References
- C++11 standard (ISO/IEC 14882:2011):
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