CODEWITHSUNDEEP
c++c++11vectorcopy
atoipowered
atoipowered

Reputation: 506

Cannot use the copy function

What is wrong with copy (which is a generic function), here? I cannot run the code.

vector<int> a(10, 2);
vector<int> b(a.size());

auto ret = copy(a.begin(), a.end(), b);

for (auto i : b) cout << i << endl;

Here's the output after compiling:

1>------ Build started: Project: Project1, Configuration: Debug Win32 ------
1>  MainEx.cpp
1>c:\program files (x86)\microsoft visual studio 11.0\vc\include\xutility(2176): error C4996: 'std::_Copy_impl': Function call with parameters that may be unsafe - this call relies on the caller to check that the passed values are correct. To disable this warning, use -D_SCL_SECURE_NO_WARNINGS. See documentation on how to use Visual C++ 'Checked Iterators'
1>          c:\program files (x86)\microsoft visual studio 11.0\vc\include\xutility(2157) : see declaration of 'std::_Copy_impl'
1>          c:\users\amin\documents\visual studio 2012\projects\project1\project1\mainex.cpp(40) : see reference to function template instantiation '_OutIt std::copy<std::_Vector_iterator<_Myvec>,std::vector<_Ty>>(_InIt,_InIt,_OutIt)' being compiled
1>          with
1>          [
1>              _OutIt=std::vector<int>,
1>              _Myvec=std::_Vector_val<std::_Simple_types<int>>,
1>              _Ty=int,
1>              _InIt=std::_Vector_iterator<std::_Vector_val<std::_Simple_types<int>>>
1>          ]
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Upvotes: 1

Views: 2302

Answers (4)

billz
billz

Reputation: 45470

std::copy 3rd parameter is an iterator, pass b.begin() instead:

 #include <iterator>
 ...

 auto ret = std::copy(a.begin(), a.end(), b.begin());

The better way is to construct b from a, in this case, compiler knows to allocate all needed memory at once and construct elements from a:

 vector<int> b(a.begin(), a.end());

or 

 std::vector<int> b = a;

Upvotes: 7

Sebastian Steger
Sebastian Steger

Reputation: 166

auto ret = copy(a.begin(), a.end(), b.begin());

should do the job.

all arguments of std::copy need to be iterators.

Upvotes: 3

juanchopanza
juanchopanza

Reputation: 227608

You need to pass an iterator, and you are passing an std::vector<int>. In your case, you should pass b.begin():

auto ret = copy(a.begin(), a.end(), b.begin());
//                                    ^^^^^^^

Of course, the simple way to achieve the same result would be

vector<int> b = a;

Upvotes: 4

Didier Trosset
Didier Trosset

Reputation: 37487

You have to copy to b.begin() as the third argument to copy is an iterator, not a container.

auto ret = copy(a.begin(), a.end(), b.begin());

Upvotes: 2

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