C++11 New data structure tuple

About tuple

A tuple is one of C + + 11 's new standard libraries, which represents an n-tuple array, which is equivalent to a struct with n members, except that the members of the struct are anonymous. A tuple is a pair-like template , a tuple is like a generalized version of a pair, a pair can hold only two members, and a tuple can have multiple members, and the same is true for a pair and a tuple to allow its members to be of different types.

Use of tuple

The most common use of a tuple is to use it as the return value of a function, which allows the function to return multiple values. (although C + + can also be implemented by structs to return multiple worthwhile capabilities, it is more cumbersome relative to a tuple.) ）

Use of tuple defines tuple

tuple<int,double,string> testtuple1;//新建tuple类型tuple<int,double,string> testtuple2(1,2.0,"test");//新建tuple类型的变量，其类型为tuple<int,double,string>auto testtuple3=make_tuple("test2",123,3.14);//通过初值来初始化tuple，其类型从初值的类型中推断。

Accessing tuple values

With the pair using first and second to get the element is different, because the number of elements of a tuple is not fixed, so you cannot use this way, the members of the tuple are unnamed, to access a tuple member, you need to use a standard library function template called GET, Since it is a function template, you need to make its template arguments,

It is important to note that N in,get< n> (type) requires a constant expression, not a variable.

auto str=get<0>(testtuple3);//访问第一个元素，注意从0开始，auto int_v=get<1>(testtuple3);//访问第二个元素。get<2>(testtuple3)=2.0;//更改第三个元素的值。

Tuple helper Functions

method to get the number of elements of a tuple

size_t sz=tupe_size<testtuple3>::value;//返回3

tupe_size< Tupletype >::value is a class template.

Gets the data type of the first element of the tuple type:

// tuple_element<i,tupletype>::type 是类模板，返回第i个元素的数据类型。cout<<tuple_element<i,tupletest3>::type<<endl;

Relational operators

Two tuple variables can be compared directly to the size, but there are prerequisites. It needs to meet two conditions:
1. Two tuples have the same number of members.
2. Each pair of members of two tuple uses the = = operator to be legal (equal or not), and if it is a relational operator, the < of each member is legal.

bool b=(testtuple1==testtuple2);bool b=(testtuple2<testtuple3);

In addition, because tuple defines the < and = = operators, we can pass the tuple series to the sorting algorithm. And in unordered containers, you can use a tuple variable as the keyword type.

Use a tuple to return multiple values to the function

tuple<int,double,string> get_tuple(){       tuple<int,double,string> tp;    ...    return tp;}auto tp=get_tuple();cout<<get<0>(tp)<<get<1>(tp)<<get<2>(tp)<<endl;

Reference material: "C + + Primer 5th"

C++11 New data structure tuple