C++ utility get function

The ‘get‘ function of <utility> returns either the first or second value of the pair<Tp1,Tp2> object.

There are three types of get function:

1 template<std::size_t Val , class Tp1, class Tp2>   T& get(pair<Tp1, Tp2>& pr) noexcept;
2 template<std::size_t Val , class Tp1, class Tp2>   T& get(pair<Tp1, Tp2>&& pr) noexcept;
3 template<std::size_t Val , class Tp1, class Tp2>   const T& get(pair<Tp1, Tp2>& pr) noexcept;

Some points to note:

*The functions are all a template functions and the first template argument is of size_t type.

*The syntax of calling the function is get<Val>( Arg ).We can differentiate whether the returned value should be either the first or the second object of the pair<Tp1,Tp2> template by mentioning the value of Val as 0 or 1.

*The return type is a reference of the type as specified by the Val value.If Val is 0 the return reference type is Tp1,if Val is 1 the type is Tp2.

*The argument can be only a pair<Tp1,Tp2> type.

*The only difference between the first and the third version given above is that the 3rd version returned a const reference.

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Code example: Using the 1st version

#include <utility>
#include <iostream>

using namespace std;

int main( )
{
pait<string , string> pr{ “New” , “Greenford” };

cout<< get<1>(pr) << endl ;

get<0>(pr)=”Happy string”; //work fine

cout<< get<0>(pr) << endl ;

cin.get( ) ;
return 0 ;
}

Output

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The second version is only call when you try to move the object instead of trying to copy the object.You can move the object by calling the function std::move.An example is given below.

Code example: Using the second version

#include <utility>
#include <iostream>

using namespace std;

int main( )
{
pait<float , char> prM{ 54.5 , ‘G’ };

cout<< get<0>(std::move(pr)) << endl ; //calls the second version

get<1>(std::move(prM))=’o’ ; //work fine

cout<< get<1>(std::move(pr)) << endl ; //calls the second version

cin.get( ) ;
return 0 ;
}

Output