为什么checked_array_iterator在没有包含的情况下工作 <iterator> 在VS2013但在VS2017中失败了？

Question

Given the following code:

#include <memory>
#include <locale>

int main() {
    auto source = std::make_unique<int[]>(16);
    auto dest = std::make_unique<int[]>(16);
    auto dp = stdext::checked_array_iterator<int*>(dest.get(), 16);
    std::copy_n(source.get(), 16, dp);
    return 0;
}

It compiles cleanly on Visual Studio 2013 by running cl.exe /EHsc <file>.cpp . However, on Visual Studio 2017 the following errors (among others) are thrown by cl.exe :

vc12.cpp(7): error C2653: 'stdext': is not a class or namespace name
vc12.cpp(7): error C2065: 'checked_array_iterator': undeclared identifier

Why does this code no longer compile?

Answer 1

The example is missing an #include <iterator> . Technically, it was also missing for Visual Studio 2013 (see Why include what you use ), but due to the chain of includes it worked there. Between Visual Studio 2013 and Visual Studio 2017 the includes of the std -headers got revamped.

The example shows #include <locale> . In the old version, #include <iterator> was part of the include-chain of locale , which is no longer the case in Visual Studio 2017.

However, the documentation of VS2017 is hard to find at the moment since it is so new. The important document can be found at doc.microsoft.com , it lists the required header <iterator> .

Answer 2

This is included in visual-studio-2017 according to the documentation: https://docs.microsoft.com/en-us/cpp/standard-library/checked-array-iterator-class However you'll need to #include <iterator> .

Though rather than pursuing correcting this, I'd entourage writing standard conformant code. The best way to do that would be to just use a statically allocated array. This will allow you to use C++'s begin , end , and size functions to work with it: https://stackoverflow.com/a/33442842/2642059

There are some cases where that wouldn't be a good suggestion, if a dynamic array is a must have, consider using a vector . If you can't abide a container then using a unique_ptr is a good way to do this, but rather than depending upon checked_array_iterator prefer maintaining your own size:

const size_t sourceSize = 16;
auto source = std::make_unique<int[]>(sourceSize);
auto dest = std::make_unique<int[]>(sourceSize);
std::copy_n(source.get(), sourceSize, dest.get())