从DLL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 ::跨越DLL ， C ++ DLL返回指向std ::的指针列表< std :: wstring> ）C ++ DLL不能返回 std :: wstring 是不安全的，因为主程序不能保证定义 std :: wstring ，因此可能会导致崩溃。

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 ，它似乎 std :: wstring 现在可以与 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:

（由于C ++ 11）
basic_string的元素连续存储，也就是说，对于[0，s.size（））中的任何n，对于basic_string s，& *（s.begin（）+ n）==& * s.begin（）+ n）可以将一个指向s [0]的指针传递给希望指向CharT []数组的第一个元素的指针的函数。

(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.

我已经通过将& s [0] 传递给预期一个 WCHAR * 缓冲区的WINAPI函数来测试它似乎工作（ std :: wstring 正确填充了WINAPI的结果）。所以因为现在， std :: wstring 可以显然被视为一个 WCHAR 数组，我决定重新访问这个问题：can从DLL中安全地返回一个 std :: wstring 为什么或为什么不这样做？

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

在DLL边界上传递C ++对象时，没有任何改变。与以前相同的原因仍然不允许。边界另一边的模块可能对类有不同的定义。

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.

& s [0] 是一个有效的可修改的指向字符数组的指针并不真正相关。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。可以分配一个不同的堆。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.

我认为可以安全地假设在一般DLL边界内传递C ++对象永远不会有效。如果您保证边界的两边都与相同的运行时实例链接，那只能是可行的。

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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