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Why do I get an undefined reference to a symbol that is defined in the library I am linking?(为什么我会得到一个未定义的引用，指向一个在我链接的库中定义的符号？)

转载 作者：bug小助手 更新时间：2023-10-28 21:33:41 26 4
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I was trying to compile an unrelated project when I got an undefined reference when using a specific function of the Raylib library.

当我使用Raylib库的特定函数时，当我尝试编译一个不相关的项目时，得到了一个未定义的引用。


I was able to reproduce this behaviour using the following test.c

我能够使用下面的测试重现这种行为。


#include <raylib.h>

int main(){
        InitWindow(500,500, "test");
        
        int w = GetRenderWidth(); // undefined reference symbol
                                                                                
        while(!WindowShouldClose()){                                            
                BeginDrawing();                                                 
                ClearBackground(BLACK);                                  
                EndDrawing();                                                   
        }                                                                       
        CloseWindow();                                                          
        return 0;                                                               
}

This code was compiled using the following command.

此代码是使用以下命令编译的。


gcc test.c -o app -L/usr/local/lib -lraylib

The resulting output was

产生的输出是


/usr/bin/ld: /tmp/ccxqgamX.o: in function `main':
code.c:(.text+0x27): undefined reference to `GetRenderWidth'
collect2: error: ld returned 1 exit status

Once I commented the offending line out however (// int w = GetRenderWidth();)
The app compiled fine and also was able run succesfully.

然而，一旦我注释掉了令人不快的一行(//int w=GetRenderWidth()；)，应用程序编译得很好，也能够成功运行。


I examined the libraylib.a library in my /usr/local/lib folder using

我使用以下命令检查了/usr/local/lib文件夹中的libraylib.a库


nm /usr/local/lib/libraylib.a | grep GetRenderWidth

This resulted in the following outputt:

这导致了以下输出：


0000000000027b1e T GetRenderWidth

From this I surmise that the symbol is actually present in the library I linked and thus my question.
Why does my compiler (both gcc and clang) report an undefined reference on GetRenderWidth() but not on other symbols from the same library?

由此，我推测该符号实际上存在于我所链接的库中，因此我的问题也是如此。为什么我的编译器(GCC和clang)在GetRenderWidth()上报告一个未定义的引用，而不是同一个库中的其他符号？


更多回答

Do you have multiple installs of Raylib? Perhaps one that is searched and used before the one in /usr/local/lib? When building, if you remove the -L/usr/local/lib option, does it still find the Raylib library?

你有多个版本的Raylib吗？也许是在/usr/local/lib中的搜索和使用之前搜索和使用的那个？在构建时，如果删除-L/usr/local/lib选项，它是否仍能找到Raylib库？

What does width: height: title: do? Are they an artifact of the code editor?

Width：Height：TITLE：做什么？它们是代码编辑器的产物吗？

@Someprogrammerdude yes it still displays the same behaviour including compiling and running when the GetRenderWidth function call is removed.

@SomeProgram是的，它仍然显示相同的行为，包括在删除GetRenderWidth函数调用时编译和运行。

@WeatherVane yes sorry that is because I use neoclide with neovim so when I copied the text it copied everything neovim was displaying, I have removed it now.

@weathervane是的，对不起，这是因为我使用了neoclide和nevim，所以当我复制文本时，它复制了nevim显示的所有内容，现在我已经删除了它。

"Why does my compiler (both gcc and clang) report an undefined reference on GetRenderWidth() but not on other symbols from the same library?" -- because the version of libraylib being linked does not provide an external definition of function GetRenderWidth(). Since the one you are examining does define one, you must be linking a different library. Possibly there's a shared-library version (libraylib.so) somewhere that is being linked in preference to the static one.

“为什么我的编译器(GCC和clang)在GetRenderWidth()上报告了一个未定义的引用，而不是同一个库中的其他符号？”--因为要链接的libraylib版本不提供GetRenderWidth()函数的外部定义。因为您正在检查的库确实定义了一个库，所以您必须链接一个不同的库。可能有一个共享库版本(libraylib.so)在某个地方优先被链接，而不是静态版本。

优秀答案推荐

Turns out that /usr/local/lib also contained a shared version of the same library which my compilers linked with. This version did not contain the GetRenderWidth symbol which is what caused my confusion. I was able to force my compiler to use the static library by replacing -lraylib with -l:libraylib.a.

原来/usr/local/lib也包含我的编译器所链接的同一个库的一个共享版本。这个版本不包含GetRenderWidth符号，这就是导致我困惑的原因。通过将-lraylib替换为-L：libraylib.a，我可以强制编译器使用静态库。


更多回答

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