Using the New C++11 Array and Tuple Containers
by Darryl Gove and Steve Clamage
Published July 2014
The C++11 standard introduces a couple of very useful container types: arrays and tuples.
About Arrays
The C++ 11 standard introduces a std::array which is equivalent to a traditional fixed length array, but is accessible through standard container methods. An array is potentially faster than a vector since it is a fixed size. Since the size of the array is known, an implementation can place the data on the stack with a locally declared std::array object.
Listing 1 shows how an array might be used.
#include <array>
#include <algorithm>
#include <iostream>
int main()
{
const int arraysize = 10;
std::array <int, arraysize> a;
for (int i=0; i<arraysize; i++)
{
a[i]=(( i*32315^393) &15);
}
std::for_each( a.begin(), a.end(),
[](int v ) { std::cout << v << '\n'; } );
}
Listing 1. Using an array
The output from compiling and running this code is shown in Listing 2.
$ CC -O -std=c++11 array.cpp
bash-3.2$ ./a.out
9
2
15
8
5
14
11
4
1
10
Listing 2. Compiling and running array example
The std::for_each loop in Listing 1 can also be rewritten using a range-based for, as shown in Listing 3. This is a shorter way of writing the same code.
#include <array>
#include <iostream>
int main()
{
std::array <int,10> a;
for (int i=0; i<10; i++)
{ a[i]=(( i*32315^393) &15); }
for( int v : a ) std::cout << v << '\n';
}
Listing 3. Using range-based for
About Tuples
A tuple is a generalization of a pair, an ordered set of heterogeneous elements. One way to imagine using a tuple is to hold a row of data in a database. The row might contain the attributes of a person, such as the person's name, age, height, and so on. All the elements might have different types, but they all belong together as one row.
In Listing 4 we store multiple tuples of integer values into a vector, and then print them out.
#include <vector>
#include <tuple>
#include <iostream>
typedef std::tuple<int,int,int> i3tuple;
int main()
{
std::vector <i3tuple> v;
for (int i=0; i<10; i++)
{
v.push_back(i3tuple(i,i*2, i*2+1) );
}
for(i3tuple t: v)
{
std::cout << std::get<0>(t) << ' ';
std::cout << std::get<1>(t) << ' ';
std::cout << std::get<2>(t) << '\n';
};
}
Listing 4. Storing and retrieving tuples from a vector
The results of compiling and running this code are shown in Listing 5.
$ CC -O -std=c++11 tuple.cpp
bash-3.2$ ./a.out
0 0 1
1 2 3
2 4 5
3 6 7
4 8 9
5 10 11
6 12 13
7 14 15
8 16 17
9 18 19
Listing 5. Compiling and running the tuple example
It is possible to create tuples without explicitly declaring the types, as shown in Listing 6.
#include <tuple>
#include <iostream>
int main()
{
auto t = std::make_tuple("String",5.2, 1);
std::cout << std::get<0>(t) << ' '
<< std::get<1>(t) << ' '
<< std::get<2>(t) << '\n';
}
Listing 6. Implicitly declaring a tuple
The output from the code in Listing 6 is shown in Listing 7.
$ CC -O -std=c++11 implicit_tuple.cpp
$ ./a.out
String 5.2 1
Listing 7. Output using implicitly declared tuple
Conclusion
The new std::array and std::tuple containers provide developers with additional ways to manage structured data efficiently.
Revision 1.1, 08/28/2014
About the Authors
Darryl Gove is a senior principal software engineer in the Oracle Solaris Studio team, working on optimizing applications and benchmarks for current and future processors. He is also the author of the books Multicore Application Programming, Solaris Application Programming, and The Developer's Edge. Find his blog at http://blogs.oracle.com/d.
Steve Clamage is a senior engineer in the Oracle Solaris Studio team and project lead for Oracle's C++ compiler. He has been the chair of the U.S. C++ Standards Committee since 1996.
