(C++) Triple

 

Container code snippet to triple all values in a container.

 

There are multiple ways to perform Triple:

• The general algorithm way using std::bind2nd
• The general algorithm way using BOOST_FOREACH
• The general algorithm way using boost::lambda
• The C++98 algorithm way on a std::vector<int>
• Using a C++11 lambda expressions on a std::vector<int>
• The for-loop way on a std::vector<int>

 

• Download the Qt Creator project 'CppTriple' (zip)

 

 

 

 

The general algorithm way using std::bind2nd

 

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#include <algorithm> #include <numeric> #include <functional> //From http://www.richelbilderbeek.nl/CppTriple.htm template <class Container> void Triple(Container& c) {   std::transform(c.begin(),c.end(),c.begin(),     std::bind2nd(std::multiplies<typename Container::value_type>(),3)); }

 

 

 

 

 

The general algorithm way using BOOST_FOREACH

 

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#include <boost/foreach.hpp> //From http://www.richelbilderbeek.nl/CppTriple.htm template <class Container> void Triple(Container& c) {   BOOST_FOREACH(typename Container::value_type& i, c)   {     i*=3;   } }

 

 

 

 

 

The general algorithm way using boost::lambda

 

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#include <algorithm> #include <boost/lambda/lambda.hpp> template <class Container> void Triple(Container& c) {   std::for_each(c.begin(),c.end(), boost::lambda::_1 *=3); }

 

 

 

 

 

The C++98 algorithm way on a std::vector<int>

 

This version is given as the answer of Exercise #9: No for-loops.

 

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#include <vector> #include <algorithm #include <numeric> //From http://www.richelbilderbeek.nl/CppTriple.htm void Triple(std::vector<int>& v) {   std::transform(v.begin(),v.end(),v.begin(),     std::bind2nd(std::multiplies<int>(),3)); }

 

 

 

 

 

Using a C++11 lambda expressions on a std::vector<int>

 

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#include <algorithm> #include <vector> //From http://www.richelbilderbeek.nl/CppTriple.htm void TripleCpp0x(std::vector<int>& v) {   std::for_each(v.begin(),v.end(),     [](int& i) { i*=3; } ); }

 

 

 

 

 

The for-loop way on a std::vector<int>

 

Prefer algorithms over loops [1][2]

 

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#include <vector> //From http://www.richelbilderbeek.nl/CppTriple.htm void Triple(std::vector<int>& v) {   const int sz = v.size();   for (int i=0; i!=sz; ++i)   {     v[i]*=3;   } }

 

 

 

 

 

References

 

1. Bjarne Stroustrup. The C++ Programming Language (3rd edition). ISBN: 0-201-88954-4. Chapter 18.12.1: 'Prefer algorithms over loops'
2. Herb Sutter and Andrei Alexandrescu. C++ coding standards: 101 rules, guidelines, and best practices. ISBN: 0-32-111358-6. Chapter 84: 'Prefer algorithm calls to handwritten loops'