问题:

我正在尝试使用名为 DCMTK 的库它使用了一些其他外部库(zlib、libtiff、libpng、libxml2、libiconv)。我从同一网站下载了这些外部库(*.LIB 和 *.h 文件)。现在，当我编译 DCMTK 库时，出现如下链接错误(793 错误):

Error   2   error LNK2005: __encode_pointer already defined in MSVCRTD.lib(MSVCR90D.dll)    LIBCMTD.lib dcmmkdir 
Error   3   error LNK2005: __decode_pointer already defined in MSVCRTD.lib(MSVCR90D.dll)    LIBCMTD.lib dcmmkdir 
Error   4   error LNK2005: __CrtSetCheckCount already defined in MSVCRTD.lib(MSVCR90D.dll)  LIBCMTD.lib dcmmkdir 
Error   5   error LNK2005: __invoke_watson already defined in MSVCRTD.lib(MSVCR90D.dll) LIBCMTD.lib dcmmkdir 
Error   6   error LNK2005: __errno already defined in MSVCRTD.lib(MSVCR90D.dll) LIBCMTD.lib dcmmkdir 
Error   7   error LNK2005: __configthreadlocale already defined in MSVCRTD.lib(MSVCR90D.dll)    LIBCMTD.lib dcmmkdir 
Error   8   error LNK2005: _exit already defined in MSVCRTD.lib(MSVCR90D.dll)   LIBCMTD.lib dcmmkdir 

文档:

这似乎是该库的一个常见错误，因此，他们确实有一个解决此问题的常见问题解答条目，其中 ( http://forum.dcmtk.org/viewtopic.php?t=35) 说:

• The problem is that the linker tries to combine different, incompatible versions of the Visual C++ runtime library into a single binary.
• This happens when not all parts of your project and the libraries you link against are generated with the same code generation options in Visual C++.

• Do not use the /NODEFAULTLIB workaround, because strange software crashes may follow. Fix the problem!

• DCMTK is by default compiled with the "Multithreaded" or "Multithreaded Debug" code generation option (the latter for Debug mode).

• Either change the project settings of all of your code to use these code generation options,
• or change the code generation for all DCMTK modules and re-compile.
• MFC users beware: DCMTK should be compiled with "Multithreaded DLL" or "Multithreaded DLL Debug" settings if you want to link the libraries into an MFC application.

其他人相同问题的解决方案:

Huge Amount of Linker Issues with Release Build Only说:

It seems that your release build is trying to link to something that was built debug. You probably have a broken dependency in your build, (or you missed rebuilding something to release by hand if your project is normally built in pieces).

More technically, you seem to be linking projects built with different C Run Time library settings, one with "Multi-Threaded", another one with "Multi-Threaded Debug". Adjust the settings for all the projects to use the very same flavour of the library and the issue should go away

问题:

直到现在，我一直认为名称修改是唯一可能导致链接失败的问题，如果它没有被标准化的话。刚才我知道还有其他事情也可以导致同样的效果。

1. “ Debug模式”(多线程调试)和“ Release模式”(多线程)是怎么回事？ 到底背后发生了什么？为什么正是这个东西导致链接错误？

2. 我想知道是否有一种叫做“单线程调试”和“单线程”的东西再次导致同样的事情。

3. 文档讨论了有关“代码生成选项”的内容。什么代码生成选项？他们是什么？

4. 文档特别警告我们不要使用/NODEFAULTLIB 解决方法。 (例如/NODEFAULTLIB :msvcrt )。为什么？我怎么会惹是生非？到底是什么？

5. 请为 MFC 用户解释文档中的最后一点。因为我稍后将在这个项目中使用 MFC。解释我们为什么要这样做？不做会有什么麻烦。
6. 还有什么想说的吗？我的意思是关于类似的错误。我对链接器及其问题非常感兴趣。所以，如果有任何类似的事情，你可以提及它们或至少一些关键字。

最佳答案

Whats up with the "Debug Mode" (Multi-Threaded Debug) and "Release Mode" (Multi-Threaded)? What exactly is happening under the hood? Why exactly this thing is causing linking error?

链接器由于多种原因拖入库。最简单的是在链接器命令行上列出一个库，或者在链接器命令行上的链接器应答文件中。但是任何目标文件，无论是在您的项目中编译还是打包到库中，也可以包含 linker options包括请求链接特定的库。事实上，Visual C++ 编译器会自动嵌入与您在编译时使用的项目选项相匹配的链接器选项。

在链接时，来自所有目标文件和静态库文件中的对象的所有链接器选项被合并。如果请求了多个 CRT 库文件名，链接器会读入所有文件名，并且会出现命名冲突，链接器不知道要使用哪一个。

I wonder if there is something called "Single-Threaded Debug" and "Single-Threaded" which again causes the same thing.

曾经有，但最近几个版本的 Visual C++ 只提供了多线程兼容库。

Documentation talks something about "Code Generation Options". What Code Generation Options? WTH are they?

看inside your project options .

Documentation specifically warns us not to use /NODEFAULTLIB workaround. (example /NODEFAULTLIB :msvcrt ). Why? How would I cause troubles? what exactly is it?

如果您使用/NODEFAULTLIB，所有存储在目标文件和库中的对象中的链接器设置都会被忽略。您最终将没有运行时库，并且可能会丢失其他库。您可以手动将它们添加回去，但这仍然是一团糟。

Please explain the last point in the documentation for MFC users. Because I'm going to use MFC later in this project. Explain Why should we do it? What troubles would it cause if I don't. Anything more you'd like to mention? I mean regarding similar errors. I'm very interested in Linker & its problems. So, if there are any similar things you can mentions them or some keywords atleast.

MFC 应用程序和 MFC 库必须使用相同的内存管理函数，以便应用程序可以释放 MFC 分配的内存，反之亦然。文件句柄和其他资源也是共享的。 MFC DLL 已编译为在 DLL 中使用 CRT，为了能够共享资源，您需要使用相同的 CRT，这意味着也要使用 DLL。

关于c++ - Link Error : xxx is already defined in *****.LIB::究竟是什么错误？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/2725815/