如何使用visual studio 2015（C ++项目）解决特定的LNK2001错误 [英] How to resolve a specific LNK2001 error using visual studio 2015 (C++ project)

问题描述

从历史上看，为了让我们的项目成功编译和链接，编译器选项'Treat WChar_t as built in type'一直设置为No.



现在我们通过使用第三部分库文件添加新功能。通过测试看来，为了成功使用这个库，上面的编译器选项必须设置为Yes或者我会得到一个链接错误：



错误LNK2001未解析的外部符号public：int __thiscall BluetoothClient :: Connect（unsigned short *）（？Connect @ BluetoothClient @@ QAEHPAG @ Z）cmj C：\dev\Products\cmj\cmj\VC7 Project\main.obj



BluetoothClient :: Connect方法接受一个LPWSTR类型的变量，它是根据WCHAR定义的，WCHAR是根据wchar_t（winnt.h）定义的。 />


如果我将编译器选项设置为yes，它将在我的测试项目中成功链接（并运行）。



但是，如果我为真实项目设置为yes，则会在项目的其他区域中导致数百个C2664编译器错误，其中wchar_t和tchar类型的变量等等，作为参数传递。



如何在不打开'Treat WChar_t as built in type'编译器选项的情况下解决此链接错误？

（如果有帮助，我可以提供更多细节）。



我尝试过：



我尝试将参数传递给BluetoothClient :: Connect以多种方式。我认为问题在于BluetoothClient :: Connect接受类型为LPWSTR的参数，该参数在wchar_t中是不定义的，这不是一个定义的类型（我不能使编译器opion on ...导致太多其他编译器错误）。



BluetoothClient :: Connect包含在库中，我没有源代码。

Historically, in order for our project to compile and link successfully the compiler option 'Treat WChar_t as built in type' has always been set to No.

Now we are adding a new feature through the use of a 3rd part library file. Through testing it appears that in order to use this library successfully the above compiler option must be set to Yes or I will get a linking error:

Error LNK2001 unresolved external symbol "public: int __thiscall BluetoothClient::Connect(unsigned short *)" (?Connect@BluetoothClient@@QAEHPAG@Z) cmj C:\dev\Products\cmj\cmj\VC7 Project\main.obj

The BluetoothClient::Connect method accepts one variable of type LPWSTR which is defined in terms of WCHAR which is defined in terms of wchar_t (winnt.h).

If I set the compiler option to yes it will link successfully (and run) in my test project.

​But, ​If I set it to yes for the real project it causes hundreds of C2664 compiler errors in other areas of the project where variables of type wchar_t and tchar, etc, are passed as arguments.

How can I resolve this linking error without turning on the 'Treat WChar_t as built in type' compiler option?
(I can provide more details if it helps).

What I have tried:

I have tried passing the argument to BluetoothClient::Connect many different ways. I think the problem is that BluetoothClient::Connect accepts an argument of type LPWSTR which is defiend in termes of wchar_t which is not a defined type (I can't tur that compiler opion on...causes too many other compiler errors).

BluetoothClient::Connect is contained ina library for whcih I do not have the source code.

推荐答案

请参阅 / Zc：wchar_t（wchar_t是原生类型） [ ^ ]：

See /Zc:wchar_t (wchar_t Is Native Type)[^]:

引用：

如果从早期版本的Visual C ++升级并遇到编译器错误C2664，因为代码试图将wchar_t隐式转换为unsigned short，我们建议您更改修复错误的代码，而不是设置/ Zc：wchar_t - 。

If you upgrade from earlier versions of Visual C++ and encounter compiler error C2664 because the code is trying to implicitly convert a wchar_t to unsigned short, we recommend that you change the code to fix the error, instead of setting /Zc:wchar_t-.

可能有一个解决方案，但我不是确定它是否有效（只需试一试）：



更改函数声明中的参数类型（例如通过编辑库头文件）到 __ wchar_t （resp。 * __ wchar_t 和 const * __ wchar_t ）并在调用函数时强制转换参数：

There may be one solution but I'm not sure if it works (just give it a try):

Change the parameter types in the function declarations (e.g. by editing the library header file) to __wchar_t (resp. *__wchar_t and const *__wchar_t) and cast the parameters when calling the functions:

// Library header file
// Old
//int Connect(LPWSTR str);
// New
int Connect(__wchar_t *str);

// Cast when calling
wchar_t lpParam[] = L"test";
BluetoothClient::Connect((__wchar_t *)lpParam);

[更新]

解决方案经过验证工作后，我会解释在这里做了什么。



取决于编译器设置， wchar_t 定义为 unsigned short 或内置类型 __ wchar_t 。



因为库是使用内置类型构建的，所以函数声明必须使用该类型才能使链接器满意。使用相同设置构建应用程序时， LPWSTR 将根据需要 __ wchar_t * 。否则 LPWSTR 将是 unsigned short * ，这会导致链接器错误。因此，更改函数声明以使用正确的类型 __ wchar_t * 可以避免链接器错误。



但是这样做编译器会抱怨传递 LPWSTR 参数（ unsigned short * ），其中预计__wchar_t * 。这可以通过将参数转换为所需类型来解决。

[/ UPDATE]

[UPDATE]
After the solution has been verified as working, I will explain what is done here.

Depending on the compiler setting, wchar_t is defined as unsigned short or the built-in type __wchar_t.

Because the library has been build using the built-in type, the function declaration must use that type to make the linker happy. When the application is build with the same setting, LPWSTR will be __wchar_t * as required. Otherwise LPWSTR will be unsigned short * which leads to the linker error. So changing the function declaration to use the correct type __wchar_t * avoids the linker error.

But when doing so the compiler would complain about passing a LPWSTR argument (which is unsigned short *) where a __wchar_t * is expected. This is solved by casting the parameter to the required type.
[/UPDATE]

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