Qt Creator：未解析的外部符号 [英] Qt Creator: Unresolved External Symbol

问题描述

我一直在挣扎一段时间，在Qt中出现错误：

  mainwindow.obj：-1： LNK2019：未解析的外部符号_git_repository_open在函数public：__thiscall中引用。MainWindow :: MainWindow（class QWidget *）（?? 0MainWindow @@ QAE @ PAVQWidget @@@ Z）
  pre> 
 
 
这显然是一个链接错误，但我还没能找出导致这种情况的原因。这是所有正在Windows上编译，我目标的库是libgit2。
 
 
 
我编译libgit2使用MVSC2010（我也用于我的Qt构建），然后将外部库添加到我的Qt项目中。包括被承认没有问题，但库没有正确链接。因为libgit2是一个C库，我试图将其包含在extern块（也没有exern块）无效：
  externC{
 #include< git2.h> 
} 
  
此外，lib文件中的 ：
  dumpbin / EXPORTS git2.lib 
 ... 
 _git_repository_open @ 8 
。 .. 
  
引发错误的相关行（第一行自行工作，因为它在git标题中定义，但是第二行在链接时失败）：
  git_repository * repo; 
 git_repository_open（& repo，/opt/libgit2-test/.git）; 
  
相关qt.pro文件行：
  win32：CONFIG（release，debug | release）：LIBS + = -L $$ PWD / libgit2 / lib / -lgit2 
 else：win32：CONFIG | release）：LIBS + = -L $$ PWD / libgit2 / lib / -lgit2d 
 else：unix：LIBS + = -L $$ PWD / libgit2 / lib / -lgit2 
 
 INCLUDEPATH + = $$ PWD / libgit2 / include 
 DEPENDPATH + = $$ PWD / libgit2 / include 
  
 
 
解决方案
看起来您遇到了这个问题：
 
 
 
  https://github.com/libgit2/libgit2/issues/741  
 
 
 
您可以从这里试用建议：
 
 
 
  https://github.com/ libgit2 / libgit2 / pull / 749＃issuecomment-6434565  
 
 
在Windows上使用MSVC工具链构建时，默认构建
使用__stdcall约定。但是这不会反映在
头文件中，所以你必须在自己的
构建中使用/ Gz编译器选项，以便能够成功地链接到libgit2构建的
的方式。如果这不可能或不可取，在初始cmake时设置
 -DSTDCALL = OFF选项。
 
 
 
I've been struggling for a while with an error in Qt:
mainwindow.obj:-1: error: LNK2019: unresolved external symbol _git_repository_open referenced in function "public: __thiscall MainWindow::MainWindow(class QWidget *)" (??0MainWindow@@QAE@PAVQWidget@@@Z)
This is obviously a linking error, but I haven't been able to figure out what is causing this. This is all being compiled on Windows, and the library that I'm targeting is libgit2.

I compiled libgit2 using MVSC2010 (which I'm also using for my Qt builds), and then added the external library to my Qt project. The includes are being acknowledged without issue, but the library isn't being linked properly. Since libgit2 is a C library, I've tried included the library in an extern block (and also without the exern block) to no avail:
extern "C" {
    #include  <git2.h>
}
Also, the function is in the lib file:
dumpbin /EXPORTS git2.lib
...
_git_repository_open@8
...
The relevant lines which are throwing an error (the first one works if on its own, since it is defined in the git header, but the second line fails upon linking):
git_repository *repo;
git_repository_open(&repo, "/opt/libgit2-test/.git");
The relevant qt.pro file lines:
win32:CONFIG(release, debug|release): LIBS += -L$$PWD/libgit2/lib/ -lgit2
else:win32:CONFIG(debug, debug|release): LIBS += -L$$PWD/libgit2/lib/ -lgit2d
else:unix: LIBS += -L$$PWD/libgit2/lib/ -lgit2

INCLUDEPATH += $$PWD/libgit2/include
DEPENDPATH += $$PWD/libgit2/include

解决方案
It looks like you ran across this problem:

https://github.com/libgit2/libgit2/issues/741

You can try the suggestion from here:

https://github.com/libgit2/libgit2/pull/749#issuecomment-6434565

  
When building on Windows with the MSVC tool chain, the default build
  uses the __stdcall convention. However this is not reflected in the
  header files, so you have to use the /Gz compiler option in your own
  build as well for being able to successfully link with a libgit2 built
  that way. If this is not possible or not desirable, set the
  -DSTDCALL=OFF option when doing the initial cmake.


                        
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