STL algorithm to copy container elements.

std::copy assumes that the memory data is copied to is valid. For example, if you copy a std::vector of size 10 to another std::vector, the latter must have a size of 10 at least. But if the size is unknown, use an inserter like std::back_inserter.

Related algorithms are:

std::copy_backward: copy values to the back of a container
std::copy_if: for performing a conditional copy
std::transform: for copy and modify

Prefer algorithm calls over hand-written loops [1][2].

Example without using an inserter


#include <algorithm

#include <cassert>

#include <iostream>

#include <map>

#include <vector>

 

int main()

{

  const int size = 10;

  //Generate a std::map

  std::map<int,int> myMap;

  for (int i=0; i!=size; ++i) myMap[i] = i*i;

  //Generate a std::vector

  std::vector<std::pair<int,int> > myVector;

  myVector.resize(size);

 

  //Copy the std::map to the std::vector

  std::copy(myMap.begin(),myMap.end(),myVector.begin());

 

  assert(myVector.size()==size);

  //Display the std::vector

  for (int i=0; i!=size; ++i)

  {

    std::cout

      << myVector[i].first

      << " "

      << myVector[i].second

      << std::endl;

  }

}

Example with using an inserter

Copies a std::map to a std::vector.


#include <algorithm

#include <cassert>

#include <iostream>

#include <map>

#include <vector>

 

int main()

{

  const int size = 10;

  //Generate a std::map

  std::map<int,int> myMap;

  for (int i=0; i!=size; ++i) myMap[i] = i*i;

  //Generate a std::vector

  std::vector<std::pair<int,int> > myVector;

 

  //Copy the std::map to the std::vector

  std::copy(myMap.begin(),myMap.end(),std::back_inserter(myVector));

 

  //Display the std::vector

  for (int i=0; i!=size; ++i)

  {

    std::cout

      << myVector[i].first

      << " "

      << myVector[i].second

      << std::endl;

  }

}

Example: Append


#include <algorithm



//From http://www.richelbilderbeek.nl

template <class Container>

void Append(Container& toWhat, const Container& whatToAppend)

{

  std::copy(whatToAppend.begin(),whatToAppend.end(),std::back_inserter (toWhat));

}

Example: CoutVector


#include <iostream>

#include <iterator>

#include <ostream>

#include <vector>



//From http://www.richelbilderbeek.nl/CppCoutVector.htm

template <class T>

void CoutVector(const std::vector<T>& v)

{

  std::copy(v.begin(),v.end(),std::ostream_iterator<T>(std::cout,"\n"));

}

Example: CoutContainer


#include <iostream>

#include <iterator>

#include <ostream>

#include <vector>



//From http://www.richelbilderbeek.nl/CppCoutContainer.htm

template <class Container>

void CoutContainer(const Container& c)

{

  std::copy(c.begin(),c.end(),

    std::ostream_iterator<typename Container::value_type>(std::cout,"\n"));

}

External links

References

Bjarne Stroustrup. The C++ Programming Language (3rd edition). ISBN: 0-201-88954-4. Chapter 18.12.1: 'Prefer algorithms to loops.
Scott Meyers. Effective STL. ISBN: 0-201-74962-9. Item 43: 'Prefer algorithm calls over hand-written loops'

Go back to Richel Bilderbeek's C++ page.

Go back to Richel Bilderbeek's homepage.