从DLL中返回std :: wstring是否安全？ [英] Is it safe to return std::wstring from a DLL?

问题描述

根据一些较旧的StackOverflow问题（无法传递std :: wstring跨DLL ， C ++ DLL将指针返回到std :: list< std :: wstring> ），认为C ++ DLL返回 std :: wstring 是不安全的，因为不能保证主程序具有相同的 std :: wstring 的定义，因此可能导致崩溃。

According to some older StackOverflow questions ( Unable to pass std::wstring across DLL , C++ DLL returning pointer to std::list<std::wstring> ) it's not considered safe for a C++ DLL to return a std::wstring because there's no guarantee the main program has the same definition of std::wstring and therefore it might cause a crash.

但是，在 http://en.cppreference.com/w/cpp/string/basic_string ，看起来 std :: wstring 可以与 WCHAR 数组互换使用：

However, in http://en.cppreference.com/w/cpp/string/basic_string , it seems std::wstring can be used interchangeably with a WCHAR array now:

（从C ++ 11开始）
basic_string的元素是连续存储的，即对于basic_string s，& *（s.begin（）+ n）对于[0，s.size（）]中的任何n，==& * s.begin（）+ n，或者等价地，指向s [0]的指针可以传递给期望指向第一个元素的CharT []数组。

(Since C++11) The elements of a basic_string are stored contiguously, that is, for a basic_string s, &*(s.begin() + n) == &*s.begin() + n for any n in [0, s.size()), or, equivalently, a pointer to s[0] can be passed to functions that expect a pointer to the first element of a CharT[] array.

我已经通过传递& s [0] / code>到一个WINAPI函数，期望一个 WCHAR * 缓冲区，它似乎工作（ std :: wstring 正确填充WINAPI的结果）。因此，由于 std :: wstring 现在看起来像一个 WCHAR 数组，我决定重新访问这个问题：can从DLL中安全地返回 std :: wstring ？为什么或为什么不？

I've tested this by passing &s[0] to a WINAPI function that expected a WCHAR* buffer and it appeared to work (the std::wstring was correctly populated with the results of the WINAPI). So since std::wstring can apparently be treated like a WCHAR array now, I decided to revisit this question: can a std::wstring be safely returned from a DLL? Why or why not?

推荐答案

关于跨DLL边界传递C ++对象没有什么变化。这仍然不允许有同样的原因。边界另一侧的模块可能有不同的类定义。

Nothing has changed with regards passing C++ objects across DLL boundaries. That is still not allowed for the same reason as before. The module on the other side of the boundary may have a different definition of the class.

事实上& s [0] code>是一个有效的可修改的指针，字符数组不是真正相关的。因为 std :: basic_string 不仅仅是一个字符数组。

The fact that &s[0] is a valid modifiable pointer to character array is not really relevant. Because a std::basic_string is a lot more than just an array of characters.

请记住， std :: basic_string 的每个实现都可以有不同的内部存储。对于 operator [] 可以有不同的实现。可以分配不同的堆。等等。

Remember that each implementation of std::basic_string can have different internal storage. Can have a different implementation for operator[]. Can be allocated off a different heap. And so on.

我认为它是安全的，假定它永远不会有效的传递C ++对象跨越一般的DLL边界。它只有在你保证边界的两边都链接到同一个运行时实例时才可行。

I think it is safe to assume that it will never be valid to pass C++ objects across general DLL boundaries. It is only viable if you guarantee that both sides of the boundary are linked against the same runtime instance.

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