tuple元組定義了一個有固定數目元素的容器,其中的每個元素型別都可以不相同,這與其他容器有著本質的區別.是對pair的泛化。
首先來介紹元組的建立和元組元素的訪問。通過make_tuple()建立元組，通過get<>()來訪問元組的元素。通過下面這段程式來認識這兩個函式的用法：
#include <iostream>
#include <tuple>
#include <functional>
int main()
{
auto t1 = std::make_tuple(10, "Test", 3.14);
std::cout << "The value of t1 is "
<< "(" << std::get<0>(t1) << ", " << std::get<1>(t1)
<< ", " << std::get<2>(t1) << ")\n";
int n = 1;
auto t2 = std::make_tuple(std::ref(n), n);//ref表示引用
n = 7;
std::cout << "The value of t2 is "
<< "(" << std::get<0>(t2) << ", " << std::get<1>(t2) << ")\n";
}
執行結果為：
The value of t1 is (10, Test, 3.14)
The value of t2 is (7, 1)
接下來介紹tie()函式。 tie()函式可以將變數連線到一個給定的tuple上，生成一個元素型別全是引用的tuple,相當於make_tuple(ref(a),ref(b),…)。可以通過tie()函式的使用方便的對tuple進行“解包”操作。看下面的程式碼：
#include <iostream>
#include <tuple>
int main ()
{
int myint;
char mychar;
float myfloat;
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 【1】
std::tie (myint,myfloat, mychar) = mytuple;
std::cout << "myint contains: " << myint << std::endl;
std::cout << "mychar contains: " << mychar << std::endl;
std::cout << "myfloat contains: "<< myfloat <<std::endl;
std::get<0>(mytuple) = 100;//修改tuple的值
std::cout <<"After assignment myint contains: "<< std::get<0>(mytuple) << std::endl;
return 0;
}
執行結果：
myint contains: 10
mychar contains: a
myfloat contains: 2.6
After assignment myint contains: 100
注：正如【1】處我們可以使用std::ignore,從而不用關聯tuple中的第二個元素.
最後介紹一個tuple_cat()函式，通過該函式可以將多個tuple連線起來形成一個tuple（注：在VC11中只能連線兩個tuple並不是真正的多個tuple）。
#include <iostream>
#include <utility>
#include <string>
#include <tuple>
int main ()
{
std::tuple<float,std::string> mytuple (3.14,"pi");
std::pair<int,char> mypair (10,'a');
auto myauto = std::tuple_cat ( mytuple, mypair );
std::cout << "myauto contains: " << std::endl;
std::cout << std::get<0>(myauto) << std::endl;
std::cout << std::get<1>(myauto) << std::endl;
std::cout << std::get<2>(myauto) << std::endl;
std::cout << std::get<3>(myauto) << std::endl;
return 0;
}
執行結果：
myauto contains:
3.14
pi
10
a