如何解决由于在Visual Studio中添加.lib文件到C ++项目的LINK错误？ [英] How to resolve LINK errors due to addition of .lib files to a C++ project in Visual Studio?

问题描述

我使用Visual Studio Pro 2012创建了一个新的c ++项目。

我试图添加C语言 1ib 文件，但我收到一些 LINK 错误：

错误2错误LNK2019：未解析的外部符号_av_malloc @ 4在函数_video_encode_example @ 4中引用D：\C-Sharp\C ++ Compiling\ConsoleApplication7\ConsoleApplication7\example.obj ConsoleApplication7

在我的部分，我在解决方案资源管理器中的项目名称 ，然后到 Linker>然后在附加依赖关系中，我已编辑，并添加了所有 .lib 档案：

  avcodec.lib 
 avdevice.lib 
 avfilter.lib 
 avformat.lib 
 avutil.lib 
  

我需要添加更多缺少的.lib文件吗？我再次查看，这些是我唯一的.lib文件。

我没有改变任何其他的链接器。在VC ++我改变了包括目录： D：\ C-Sharp\C ++ Compiling\ConsoleApplication4\ConsoleApplication1\include

include 目录每个目录中都有一些目录以及一些头文件。

参考目录和库目录已更改两个到同一目录：'D：\c ++ dev\ffmpeg-20130418-git-ee94362-win64-dev\lib'.在此目录中有 Lib 文件， DEF 文件和一些 A 文件。

如何解决这些错误？

**我在google中搜索我试图将子系统更改为控制台，但它没有帮助。
**我已经有主要功能：

  #includestdafx.h
 #include targetver.h
 
 int _tmain（int argc，_TCHAR * argv []）
 {
 
 return 0; 
} 
  

我有8个LINK错误，错误编号9是：

错误10错误LNK1120：8未解析的外部D：\C-Sharp\C ++ Compiling\ConsoleApplication7\Debug\ConsoleApplication7.exe 1 1 ConsoleApplication7

我还能做些什么来解决这个问题？

** EDIT **

将项目目标更改为x64现在我只有两个链接错误：

错误2错误LNK2019：未解析的外部符号avcodec_open在函数video_encode_example中引用D：\C -Sharp \C ++ Compiling\ConsoleApplication7\ConsoleApplication7\example.obj ConsoleApplication7

和

错误3错误LNK1120：1未解析的外部D：\C-Sharp\C ++ Compiling\ConsoleApplication7\x64\Debug\ConsoleApplication7.exe 1 1 ConsoleApplication7

试图双击它们，但什么也没有。我现在不知道该怎么办。

解决方案

我在你的问题中发现你使用ffmpeg库。 / p>

如果你想将这些链接到一个C ++项目，你必须确保你包装 #include 语句在 externC块中，像这样：

  extern C
 {
 #includeavformat.h//等等。
} 
  

这将通过确保导入的函数名在导入时不会被破坏来修复链接错误。

I've created a new c++ project with Visual Studio Pro 2012.

I tried to add C language 1ib files,but I'm getting some LINK errors like:

Error 2 error LNK2019: unresolved external symbol _av_malloc@4 referenced in function _video_encode_example@4 D:\C-Sharp\C++ Compiling\ConsoleApplication7\ConsoleApplication7\example.obj ConsoleApplication7

On my part I went to "Properties" on my "Project Name" in the Solution Explorer, then to Linker > Input and then at the top,in Additional Dependencies I did edit and added all the .lib files:

avcodec.lib
avdevice.lib
avfilter.lib
avformat.lib
avutil.lib

Do I need to add more missing .lib files ? I looked again and these are the only .lib files I have.

I didn't change anything else in the Linker.In the VC++ I changed the Include Directories to: D:\C-Sharp\C++ Compiling\ConsoleApplication4\ConsoleApplication1\include

In the include directory there are some directories in each directory along with some header files.

The reference directories and library directories changed both to the same directory: 'D:\c++dev\ffmpeg-20130418-git-ee94362-win64-dev\lib'.In this directory there are Lib files,DEF files and some A files.

How can I resolve these errors ?

** I search in google i tried to change the SubSystem to Console but it didn't help. ** I have main function already:

#include "stdafx.h"
#include "targetver.h"

int _tmain(int argc, _TCHAR* argv[])
{

    return 0;
}

I have 8 LINK errors and error number 9 is:

Error 10 error LNK1120: 8 unresolved externals D:\C-Sharp\C++ Compiling\ConsoleApplication7\Debug\ConsoleApplication7.exe 1 1 ConsoleApplication7

What else can i do to resolve this problems ?

** EDIT **

Changed the project target to x64 now i have only two link erros:

Error 2 error LNK2019: unresolved external symbol avcodec_open referenced in function video_encode_example D:\C-Sharp\C++ Compiling\ConsoleApplication7\ConsoleApplication7\example.obj ConsoleApplication7

And

Error 3 error LNK1120: 1 unresolved externals D:\C-Sharp\C++ Compiling\ConsoleApplication7\x64\Debug\ConsoleApplication7.exe 1 1 ConsoleApplication7

Tried to make double click on them but nothing. I'm not sure what to do now.

解决方案

I just spotted in your question that you're using ffmpeg libraries.

If you want to link these into a C++ project, you have to make sure that you wrap the #include statements in an extern "C" block, like this:

extern "C"
{
    #include "avformat.h"   // etc. etc.
}

This will fix the link errors by making sure that the exported function names are not mangled on import.

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