What are Tuples?
In C++ language, the classes work as user defined data types. The class contains both data and function together. Therefore, to make the data more and more organized, C++11 has introduced a new concept of tuple. Tuples give very good flexibility for creating a collection of different or same data types.
In a class, we can access a data member or function using its name. However, in a tuple we use get<index> helper function for the same. Undoubtedly, in Object Oriented programming, the Tuple concept provides much more power for creating and handling multiple user defined data.
Header file required
#include<tuple>How to define tuple data type
std::tuple<int,int> t1 (5,5);
// t1 tuple holding 2 int values
std::tuple<int,char,float>t2(5,'a',34.3);
// t2 tuple holding int, char and float values
std::tuple<char,string,float>t3('a',"MainFunda".23.80);
// t3 tuple holding char, string and float Basic Example of tuple in C++
Lets us create a Sample application for seeing how to set and get data from tuples
#include <iostream> //Main header file
#include <string> // for string
#include <tuple> //for tuple
using namespace std;
int main()
{
std::tuple<int, float, char,std::string> t1
(5,23.8,'a',"MainFunda");
//created tuple holding 4 data values
int iData = std::get < 0 > (t1);
// get 1st int value
float fData= std::get < 1 > (t1);
// get 2nd float value
char cData = std::get<2>(t1);
// get 3rd char vaue
std::string strData = std::get < 3 > (t1);
// get 3rd char value
cout <<"Int is "<< iData
<<"\nFloat is "<<fData
<<"\nChar is "<<cData
<<"\nString is "<<strData
<<endl;
return 0;
}As seen above getting data from a tuple object is very easy . We just need to call get<index-1> for knowing the content of data from tuple.
Error scenario with invalid get<index>
Lets see one more application where we are calling get<index-1> with invalid index
#include <iostream> //Main header file
#include <string> // for string
#include <tuple> //for tuple
using namespace std;
int main()
{
std::tuple<int, float, char,std::string> t1
(5,23.8,'a',"MainFunda");
//created tuple holding 4 data values
int iData = std::get < 5 > (t1);
// get 5th (invalid) value
cout <<"Int is "<< iData
<<endl;
return 0;
}We are getting compile time error for accessing invalid index for tuple. This is the advantage of tuple .
Tuple – Helper Function
get( )
The function get( ) takes an integer index as input and returns the reference to tuple data member at that index . In turn, we can use such reference for setting a tuple data member also. Below application demonstrates this
#include <iostream> //Main header file
#include <string> // for string
#include <tuple> //for tuple
using namespace std;
int main()
{
std::tuple<int, float, char,std::string> t1
(5,23.8,'a',"MainFunda");
//created tuple holding 4 data values
int iData = std::get < 0 > (t1);
// get first data member of tuple
cout <<"Int is "<< iData
<<endl;
std::get<0>(t1) = 30;
// set first data member of tuple
iData = std::get<0>(t1);
cout <<"Int after modification "
<< iData
<<endl;
return 0;
}Output
tuple_size( )
At any time we can get the size of tuple by using tuple_size( ) function.
#include <iostream> // main header
#include <tuple> // tuple header
#include<string> // string header
using namespace std;
int main ()
{
std::tuple<int,char,float,std::string> t1
(1,'a',1.1,"MainFunda");
cout << "size of tuple is "
<<std::tuple_size<decltype(t1)>::value
<< endl;
// value contain the number of elements
return 0;
}Output
make_tuple( )
The function make_tuple( ) is used for creating a tuple from a list of elements passed in the arguments. List of elements which we are passing as argument can be of different data types.
#include <iostream> //main header
#include <tuple> // for tuple
using namespace std;
int main()
{
auto t1 = std::make_tuple(1,2.4, "MainFunda");
// tuple creation
cout << "The value of t1 is "
<< std::get<0>(t1)
<< ", "
<< std::get<1>(t1)
<< ", "
<< std::get<2>(t1)
<<endl;
}Output
forward_as_tuple( )
The function forward_as_tuple( ) creates a temporary tuple as r-value reference from argument passed as parameter to this function.
// forward_as_tuple example
#include <iostream> // main header
#include <tuple> // for tuple
using namespace std;
void show_Data(std::tuple<int&&, int&&> t1)
{
std::cout << std::get<0>(t1)
<< ", "
<< std::get<1>(t1)
<< endl;
}
int main()
{
show_Data (std::forward_as_tuple(30,30));
return 0;
}Output
tuple_cat( )
The function tuple_cat( ) concatenates two or more tuples which are passed as the arguments.
#include <iostream> //main header
#include <string> // for string
#include <tuple> // for tuple
using namespace std;
int main () {
std::tuple<char,std::string> t1 ('c',"MainFunda");
std::pair<int,float> t2 (100,12.5);
auto t3 = std::tuple_cat ( t1, t2 );
std::cout << "ConCat T3" <<endl ;
std::cout << std::get<0>(t3) << endl;
std::cout << std::get<1>(t3) << endl;
std::cout << std::get<2>(t3) << endl;
std::cout << std::get<3>(t3) << endl;
auto t4 = std::tuple_cat(t3,
std::make_tuple(" test",
"begin"));
std::cout << "ConCat T4" <<endl ;
std::cout << std::get<0>(t4) << endl;
std::cout << std::get<1>(t4) << endl;
std::cout << std::get<2>(t4) << endl;
std::cout << std::get<3>(t4) << endl;
std::cout << std::get<4>(t4) << endl;
std::cout << std::get<5>(t4) << endl;
return 0;
}Output
What are Pairs in C++?
Pairs creates class template from 2 different or same datatypes . It is a specialized version of tuple with 2 elements.
Header File required for pairs
#include <utility>Basic example of Pairs
lets see below simple example for creating and displaying the Pair content
#include <iostream> // main header
#include <utility> // for pair
using namespace std;
int main ()
{
std::pair <int,float> p1 (1,2);
std::cout << "foo: "
<< p1.first
<< ", "
<< p1.second
<< endl;
return 0;
}Output
Pair-Helper Functions
make_pair( )
This function creates a pair object from its first and second argument.
#include <iostream> // main header
#include <utility> // for pair
using namespace std;
int main () {
std::pair <int,float> p1 = make_pair(1,2);
std::cout << "foo: "
<< p1.first
<< ", "
<< p1.second
<< endl;
return 0;
}Output
What is a Tie of in C++?
We have read tuple data types above. A tie creates an L-vlaue tuple for future use. Tie is mainly used for extracting element from tuple.
Basic Example with Tie
// packing/unpacking tuples
#include <iostream> // std::cout
#include <tuple> // std::tuple, std::make_tuple, std::tie
int main ()
{
int i1;
float f1;
std::tuple<int,float> t1 = std::make_tuple (1, 22.3);
// packing values into tuple
std::tie (i1,f1) = t1; //unpacking tuple into variables
std::cout << "1st element "
<< i1
<< '\n';
std::cout << "2nd element: "
<< f1 << '\n';
//example to ignore some element
std::tie (i1, std::ignore) = t1;
// unpacking tuple into variables
//and ignoring 2ns element
std::cout << "1st element "
<< i1
<< '\n';
return 0;
}Output
Main Funda: Tuples provides additional flexibility to play around with user-defined data types