C++ Copy an array created with new

Question

I have created two arrays List1 and List2 with new in C++. List1 is updated with data. I would like to copy List1 to List2. I tried using

std::copy(std::begin(List1), std::end(List1), std::begin(List2));

However, this does not work and gives the following error message:

error: ‘begin’ is not a member of ‘std’

Any possible suggestions for this error? Or alternative ways to copy in C++?

@KerrekSB : Instead of new? I would not like to change this to std::vector, as the code is already under distribution. — SKPS, Oct 08 '13 at 16:41
Is list2 big enough? Are you *sure* you want to copy the data? — doctorlove, Oct 08 '13 at 16:44
Maybe your compiler is missing support for this feature specifically, although I don't know of any that are off the top of my head. — chris, Oct 08 '13 at 16:45
You can use [std::array](http://stackoverflow.com/a/16137997/1560509) — memo1288, Oct 08 '13 at 16:49
Don't use begin and end then, just give it the first and one beyond the last members. std::copy(&List1[0], &List1[whatever_size_you_newed], List2); — doctorlove, Oct 08 '13 at 16:51
VS2012 gives different error messages, like `could not deduce template argument for '_Ty (&)[_Size]' from 'int *'` — doctorlove, Oct 08 '13 at 16:58

score 2 · Answer 1 · answered Oct 08 '13 at 16:45

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"I have created two arrays List1 and List2 with new in C++"

The begin and end free functions won't work on a pointer.

Even if everything is correct, you may end up with no matching call to begin(T *&)

T is the type of your pointer.

Use std::vector or std::list other STL container or just simply static arrays to work with std::begin and std::end

answered Oct 08 '13 at 16:45

P0W

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Is there an explanation? or they just didn't include its support – khajvah Oct 08 '13 at 16:46
@POW: Would you recommend using memcpy? – SKPS Oct 08 '13 at 16:51
@khajvah See [this](http://en.cppreference.com/w/cpp/iterator/begin), probably it answers your question – P0W Oct 08 '13 at 16:51
@SathishKrishnan that's why I asked what the arrays were. That will go wrong if the constructors need to do work – doctorlove Oct 08 '13 at 16:52
@P0W isn't that link saying std::begin *does* work on `a`, given `int a[] = { -5, 10, 15 };`? – doctorlove Oct 08 '13 at 16:54
@doctorlove yes I told for static array, it will work, see the answer. Also, here if a is passed in a function it won't, as arrays decays to pointer – P0W Oct 08 '13 at 16:55
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@khajvah The explanation is simply that a pointer is a pointer, not an array. A pointer can point to the start of an array (e.g., allocated with `new[]`), but there is no portable way to tell if it does, or how big that array is. This means that implementing `end()` is essentially impossible, and it would seem pointless to provide `begin()` without `end()`. – Mikael Persson Oct 08 '13 at 16:57

score 0 · Answer 2 · answered Oct 08 '13 at 16:43

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Put this line towards the top of your cpp file:

#include <iterator>

answered Oct 08 '13 at 16:43

Duncan Smith

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score 0 · Answer 3 · answered Oct 08 '13 at 16:43

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To use std::begin and std::end you need to include <iterator> and make sure your compiler supports C++11. However this won't fix your problem, as you cannot use them with pointers. Use std::vector instead.

answered Oct 08 '13 at 16:43

Neil Kirk

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C++ Copy an array created with new

3 Answers3