blocks|key|174218|text|在许多其他语言中，您所需要的就是头文件的等价物。但是Windows上常见的C链接器总是使用导入库，C%2B%2B链接器也是如此，现在改变可能已经太晚了。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|174219|作为一个思维实验，我们可以想象这样的语法：|174220|__declspec(dllimport,+"kernel32")+void+__stdcall++Sleep(DWORD+dwMilliseconds);|code-block|syntax|javascript|174221|有了这些信息，编译器/链接器工具链就可以完成剩下的工作。|174222|再举一个例子，在Delphi中，可以使用隐式链接导入此函数，如下所示：|174223|procedure+Sleep(dwMilliseconds:+DWORD);+stdcall;+external+'kernel32';|174224|这表明导入库对于链接到DLL来说并不是必须的。|174225|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|X|8|@]|9|@]|A|$G|H]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

In many other languages, the equivalent of the header file is all you need. But the common C linkers on Windows have always used import libraries, C++ linkers followed suit, and it's probably too late to change.

As a thought experiment, one could imagine syntax like this:

<pre><code>__declspec(dllimport, "kernel32") void __stdcall Sleep(DWORD dwMilliseconds);
</code></pre>

Armed with that information the compiler/linker tool chain could do the rest.

As a further example, in Delphi one would import this function, using implicit linking, like so:

<pre><code>procedure Sleep(dwMilliseconds: DWORD); stdcall; external 'kernel32';
</code></pre>

which just goes to show that import libraries are not, a priori, essential for linking to DLLs.

blocks|key|3783649|text|这是一个所谓的“导入库”，它包含稍后(在加载时)要求操作系统加载DLL的最小连接。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3783650|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

That is a so-called "import library" that contains minimal wiring that will later (at load time) ask the operating system to load the DLL.

blocks|key|1883414|text|DLL是Windows+(MS/Intel)的东西。(生成的)+lib包含调用DLL所需的代码，它向应用程序的其余部分公开“普通”函数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1883415|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

DLLs are a Windows (MS/Intel) thing. The (generated) lib contains the code needed to call into the DLL and it exposes 'normal' functions to the rest of your App.

blocks|key|3498364|text|不，头文件并不是必须的。头文件可以只包含函数和类的声明以及您需要的其他东西，而不是它们的实现。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3498365|这段代码之间有很大的不同：|3498366|void+Multiply(int+x,+int+y);|code-block|syntax|javascript|3498367|这段代码是：|3498368|void+Multiply(int+x,+int+y)
{
+++return+x+*+y;
}|3498369|第一个是声明，第二个是定义或实现。通常第一个示例放在头文件中，第二个示例放在.CPP文件中(如果您正在创建库)。如果您在第一个头中包含了一个头，但没有链接任何内容，那么您的应用程序如何知道如何实现Multiply？|3498370|现在，如果您使用的头文件包含全部内联的代码，则不需要链接任何内容。但是，如果有一个方法没有内联，而是在编译成.lib文件的.CPP文件中实现，那么就需要在.lib文件中进行链接。|3498371|编辑通过使用Import+Libraries，您将告诉链接器不要将导入的代码的实现详细信息包含到您的二进制文件中。相反，操作系统将在运行时将导入DLL加载到您的进程中。这将使您的应用程序更小，但您必须随附另一个DLL。如果库的实现发生变化，您只需向客户重新安装另一个DLL，而不必重新安装整个应用程序。|3498372|还有另一种选择，你可以只链接到一个库中，而不需要发布另一个DLL。该选项是链接器将实现包含到您的应用程序中的地方，使其更大。如果您必须更改导入库中的实现细节，则必须重新编译和重新链接整个应用程序，并将整个过程重新封装给您的客户。|3498373|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|11|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|12|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|13|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|14|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

No, the header file isn't necassarily enough. The header file can contain just the declarations of the functions and classes and other things you need, not their implementations.

There is a world of difference between this code:

<pre><code>void Multiply(int x, int y);
</code></pre>

and this code:

<pre><code>void Multiply(int x, int y)
{
 return x * y;
}
</code></pre>

The first is a declaration, and the second is a definition or implementation. Usually the first example is put in header files, and the second one is put in .CPP files (If you are creating libraries). If you included a header with the first and didn't link in anything, how is your application supposed to know how to implement Multiply?

Now if you are using header files that contain code that is ALL inlined, then you do not need to link anything. But if even one method is NOT inlined, but has its implementation in a .CPP file that is compiled to a .lib file, than you need to link in the .lib file.

[EDIT]
With your use of Import Libraries, you are telling the linker to NOT include the implementation details of the imported code into your binary. Instead the OS will then load the import DLL at run-time into your process. This will make your application smaller, but you have to ship another DLL with it. If the implementation of the library changes, you can just reship another DLL to your customers, and not have to reship the entire application.

There is another option where you can just link in a library and you don't need to ship another DLL. That option is where the Linker will include the implementation into your application, making it bigger in size. If you have to change the implementation details in the imported library, then you have to recompile and relink your entire application, and reship the entire thing to your customers.

blocks|key|3498438|text|在构建过程中有两个相关的阶段：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3498439|3498440|编译:从源代码到目标文件。在编译过程中，编译器需要知道哪些外部内容是可用的，因为这需要一个声明。要在多个编译单元中使用的声明在标题中进行分组。所以你需要静态库的library.|unordered-list-item|3498441|linking:的头文件，你需要库的编译版本。对于动态库，在Unix中您需要该库，在windows中，您需要“导入库”。|3498442|3498443|您可能认为库也可以嵌入声明，或者头文件可以包含需要链接的库。第一个通常是在其他语言中完成的。第二种方法有时可以通过C和C%2B%2B中的编译指示来实现，但是没有标准的方法来实现这一点，并且会与常用用法冲突(例如，从为相同声明提供代码变体的几个库中选择一个库，例如调试/释放单线程/多线程)。而且，这两种选择都不能很好地与起源于60年代的C和C%2B%2B的简单编译模型相对应。|3498444|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|N|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|O|8|@]|9|@]|A|$]]|$1|F|3|G|5|E|7|P|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|L|$]]

There are two relevant phases in the building process here:

<ul>
<li>compilation: from the source code to an object file. During the compilation, the compiler needs to know what external things are available, for that one needs a declaration. Declarations designed to be used in several compilation units are grouped in header. So you need the headers for the library.</li>
<li>linking: For static libraries, you need the compiled version of the library. For dynamic libraries, in Unix you need the library, in windows, you need the "import library".</li>
</ul>

You could think that a library could also embed the declarations or the header could include the library which needs to be linked. The first is often done in other languages. The second is sometimes available through pragmas in C and C++, but there is no standard way to do this and would be in conflict with common usage (such as choosing a library among several which provide code variant for the same declarations, for instance debug/release single thread/multithreads). And neither choice correspond well with the simple compilation model of C and C++ which has its roots in the 60's.

blocks|key|3498482|text|头文件由编译器使用。它包含将要使用的函数、类和全局变量的所有正向声明。它还可能包含一些内联函数定义。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3498483|编译器使用它们来为其提供编译代码所需的最少信息。它不会包含实现的详细信息。|3498484|然而，你仍然需要链接所有的函数，以及你已经告诉编译器的变量定义。否则将导致链接器错误。通常，这包含在其他目标文件中，这些目标文件可以连接到单个静态库中。|3498485|在使用DLL+(或.so文件)的情况下，我们仍然需要告诉链接器在DLL或共享对象中缺少的符号在哪里。在windows上，此信息包含在.lib文件中。这将生成在运行时加载和链接代码的代码。|3498486|在unix上，dll和lib文件被合并到一个.so文件中，您必须链接到关于链接器错误的链接。|3498487|您仍然可以在没有.lib文件的情况下使用dll，但是您必须使用操作系统API手动加载和链接所有符号。|3498488|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|P|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|Q|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|R|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|S|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|M|$]]

The header file is consumed by the compiler. It contains all the forward declarations of functions, classes and global variables that will be used. It may also contain some inline function definitions as well.

These are used by the compiler to give it the bare minimum information that it needs to compile your code. It will not contain the implementation details.

However you still need to link in all the function, and variable definitions that you have told the compiler about. Failure to do so will result in a linker error. Often this is contains in other object files which may be joined into a single static library.

In the case of DLLs (or .so files), we still need to tell the linker where in the DLL or shared object the missing symbols are. On windows, this information is contained in a .lib file. This will generate the code to load and link the code at runtime. 

On unix the the dll and lib files are combined into a single .so file which you must link against to about linker errors.

You can still use a dll without a .lib file but you will then have to load and link in all the symbols manually using operating system APIs.

blocks|key|1883589|text|从1000英尺开始，lib包含dll导出的函数列表和调用所需的地址。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1883590|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

from 1000 ft, the lib contains the list of the functions that dll exports and addresses that are needed for the call.

I am creating a project that uses a DLL. To build my project, I need to include a header file, and a lib file. Why do I need to include the respective lib file? shouldn't the header file declare all the needed information and then at runtime load any needed library/dll?

Thanks

why do I need to link a lib file to my project?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在创建一个使用DLL的项目。要构建我的项目，我需要包含一个头文件和一个lib文件。为什么我需要包含相应的lib文件？头文件不是应该声明所有需要的信息，然后在运行时加载任何需要的库/dll吗？谢谢

问为什么我需要将lib文件链接到我的项目？
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