C++文档阅读笔记-Tuples in C++

Posted 2022-08-17 IT1995

tuple是什么

tuple是个对象，这个对象能放很多元素，这些元素可以是不同类型的，这些元素在tuple中存储的顺序和放入tuple时的顺序一致。

tuple的操作

1.get()：可以获取tuples中的数据并且也能修改他们，通过索引下标能直接获取tuple中的元素。

2.make_tuple()：设置tuple中的值，设置的顺序就是索引的顺序，这里要注意，程序员是从0开始计数的。

如下代码：

// C++ code to demonstrate tuple, get() and make_pair()
#include<iostream>
#include<tuple> // for tuple
using namespace std;
int main()

    // Declaring tuple
    tuple <char, int, float> geek;
  
    // Assigning values to tuple using make_tuple()
    geek = make_tuple('a', 10, 15.5);
  
    // Printing initial tuple values using get()
    cout << "The initial values of tuple are : ";
    cout << get<0>(geek) << " " << get<1>(geek);
    cout << " " << get<2>(geek) << endl;
  
    // Use of get() to change values of tuple
    get<0>(geek) = 'b';
    get<2>(geek) =  20.5;
  
     // Printing modified tuple values
    cout << "The modified values of tuple are : ";
    cout << get<0>(geek) << " " << get<1>(geek);
    cout << " " << get<2>(geek) << endl;
  
    return 0;

输出如下：

The initial values of tuple are : a 10 15.5
The modified values of tuple are : b 10 20.5

上面的代码中使用get()函数后修改了第一个元素的值和第三个元素的值。

3.tuple_size()：返回当前tuple中元素的个数。

//C++ code to demonstrate tuple_size
#include<iostream>
#include<tuple> // for tuple_size and tuple
using namespace std;
int main()

  
    // Initializing tuple
    tuple <char,int,float> geek(20,'g',17.5);
  
    // Use of size to find tuple_size of tuple
    cout << "The size of tuple is : ";
    cout << tuple_size<decltype(geek)>::value << endl;
  
    return 0;
  

输出如下：

The size of tuple is : 3

4.swap()：交换2个tuples的值。

//C++ code to demonstrate swap()
#include<iostream>
#include<tuple> // for swap() and tuple
using namespace std;
int main()

  
    // Initializing 1st tuple
    tuple <int,char,float> tup1(20,'g',17.5);
      
    // Initializing 2nd tuple
    tuple <int,char,float> tup2(10,'f',15.5);
      
    // Printing 1st and 2nd tuple before swapping
    cout << "The first tuple elements before swapping are : ";
    cout <<  get<0>(tup1) << " " << get<1>(tup1) << " "
         << get<2>(tup1) << endl;
    cout << "The second tuple elements before swapping are : ";
    cout <<  get<0>(tup2) << " " << get<1>(tup2) << " " 
         << get<2>(tup2) << endl;
      
    // Swapping tup1 values with tup2
    tup1.swap(tup2);
      
    // Printing 1st and 2nd tuple after swapping
    cout << "The first tuple elements after swapping are : ";
    cout <<  get<0>(tup1) << " " << get<1>(tup1) << " " 
         << get<2>(tup1) << endl;
    cout << "The second tuple elements after swapping are : ";
    cout <<  get<0>(tup2) << " " << get<1>(tup2) << " " 
         << get<2>(tup2) << endl;
  
    return 0;

输出：

The first tuple elements before swapping are : 20 g 17.5
The second tuple elements before swapping are : 10 f 15.5
The first tuple elements after swapping are : 10 f 15.5
The second tuple elements after swapping are : 20 g 17.5

5.tie()：把tuples中某个元素分离出来，如下面tie()中的两个变量，一个带有“ignore”，一个无“ignore”

如下代码：

// C++ code to demonstrate working of tie()
#include<iostream>
#include<tuple> // for tie() and tuple
using namespace std;
int main()
   
    // Initializing variables for unpacking
    int i_val;
    char ch_val;
    float f_val;   
      
    // Initializing tuple
    tuple <int,char,float> tup1(20,'g',17.5);
  
    // Use of tie() without ignore
    tie(i_val,ch_val,f_val) = tup1;
      
    // Displaying unpacked tuple elements
    // without ignore
    cout << "The unpacked tuple values (without ignore) are : ";
    cout << i_val << " " << ch_val << " " << f_val;
    cout << endl;
      
    // Use of tie() with ignore
    // ignores char value
    tie(i_val,ignore,f_val) = tup1;
      
    // Displaying unpacked tuple elements
    // with ignore
    cout << "The unpacked tuple values (with ignore) are : ";
    cout << i_val  << " " << f_val;
    cout << endl;
  
    return 0;
  

输出：

The unpacked tuple values (without ignore) are : 20 g 17.5
The unpacked tuple values (with ignore) are : 20 17.5

6.tuple_cat()：将2个tuples构造成一个新的tuple

代码如下：

// C++ code to demonstrate working of tuple_cat()
#include<iostream>
#include<tuple> // for tuple_cat() and tuple
using namespace std;
int main()

    // Initializing 1st tuple
    tuple <int,char,float> tup1(20,'g',17.5);
  
    // Initializing 2nd tuple
    tuple <int,char,float> tup2(30,'f',10.5);
      
    // Concatenating 2 tuples to return a new tuple
    auto tup3 = tuple_cat(tup1,tup2);
      
    // Displaying new tuple elements
    cout << "The new tuple elements in order are : ";
    cout << get<0>(tup3) << " " << get<1>(tup3) << " ";
    cout << get<2>(tup3) << " " << get<3>(tup3) << " ";
    cout << get<4>(tup3) << " " << get<5>(tup3) << endl;
  
    return 0;

输出如下：

The new tuple elements in order are : 20 g 17.5 30 f 10.5