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copy_if is an algorithm that was dropped
from the C++98 STL by accident, but added to the
C++11 STL.
std::copy_if is an algorithm that was dropped
from the C++98 STL by accident.
Prefer algorithm calls over hand-written loops [1][2].
std::copy_if is an algorithm similar to
std::copy, except that a predicate can also
be supplied. std::copy_if resides in the C++11
STL header file algorithm.
#include <algorithm>
#include <cassert>
#include <vector>
int main()
{
//C++11 initializer list
const std::vector<int> v = { 0,1,2,3,4,5,6 };
//Only copy the even values to w
//using C++11 lambda expression
std::vector<int> w;
std::copy_if(v.begin(), v.end(),
std::back_inserter(w),
[](const int i) { return i % 2 == 0; } );
//Check all even values are indeed copied
//using another C++11 initializer list
assert(w == std::vector<int>( { 0,2,4,6 } ) );
}
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Prefer algorithm calls over hand-written loops [1][2].
- Bjarne Stroustrup. The C++ Programming Language (3rd edition). 1997. 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'
copy_if.h
//---------------------------------------------------------------------------
/*
Copy_if, what should have been std::copy_if
Copyright (C) 2011 Richel Bilderbeek
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
//---------------------------------------------------------------------------
//From http://www.richelbilderbeek.nl/CppCopy_if.htm
//---------------------------------------------------------------------------
#ifndef COPY_IF_H
#define COPY_IF_H
//---------------------------------------------------------------------------
//Copy_if was dropped from the standard library by accident.
//From http://richelbilderbeek.nl/CppCopy_if.htm
template<typename In, typename Out, typename Pred>
Out Copy_if(In first, In last, Out res, Pred Pr)
{
while (first != last)
{
if (Pr(*first))
*res++ = *first;
++first;
}
return res;
}
//---------------------------------------------------------------------------
#include <string>
#include <vector>
//---------------------------------------------------------------------------
struct Copy_if_version
{
static const std::string GetVersion()
{
return "2.0";
}
static const std::vector<std::string> GetVersionHistory()
{
std::vector<std::string> v;
v.push_back("2011-xx-xx: Version 1.0: initial version");
v.push_back("2011-06-22: Version 2.0: added versioning");
return v;
}
};
//---------------------------------------------------------------------------
#endif // COPY_IF_H
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std::copy_if
std::copy_if