如何解决这个一个或多个多重定义符号发现错误？

Question

以下项目中的错误是什么？

ma​​in.cpp

#include "template_specialization_conflict_test.hpp"

int main()
{
    std::cout << utils::my_template_function(0.555);
    std::cout<<utils::my_template_function<double>(0.555);
    return 0;
}

template_specialization_conflict_test.hpp

#ifndef UTILS__UTILS__UTILS__UTILS
#define UTILS__UTILS__UTILS__UTILS
#include <iostream>

namespace utils
{
    // A generic function
    template <class T>
    T my_template_function(T parameter)
    {
        std::cout << "function template";
        std::cout << parameter;
        return parameter;
    }

    // Template Specialization
    //      A function specialized for double data type
    template <>
    double my_template_function<double>(double parameter)
    {
        std::cout << "function specialization on double";
        std::cout << parameter;
        return parameter;
    }
}
#endif

template_specialization_conflict_test.cpp

#include "template_specialization_conflict_test.hpp"

namespace utils
{
    //empty
}

错误

>------ Rebuild All started: Project: template_specialization_conflict_test, Configuration: x64-Debug ------
  [1/1] Cleaning all built files...
  Cleaning... 2 files.
  [1/3] Building CXX object CMakeFiles\template_specialization_conflict_test.dir\main.cpp.obj
  [2/3] Building CXX object CMakeFiles\template_specialization_conflict_test.dir\template_specialization_conflict_test.cpp.obj
  [3/3] Linking CXX executable template_specialization_conflict_test.exe
  FAILED: template_specialization_conflict_test.exe 
  cmd.exe /C "cd . && "C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\Common7\IDE\CommonExtensions\Microsoft\CMake\CMake\bin\cmake.exe" -E vs_link_exe --intdir=CMakeFiles\template_specialization_conflict_test.dir --rc=C:\PROGRA~2\WI3CF2~1\10\bin\10.0.17763.0\x64\rc.exe --mt=C:\PROGRA~2\WI3CF2~1\10\bin\10.0.17763.0\x64\mt.exe --manifests  -- "C:\PROGRA~2\Microsoft Visual Studio\2019\Professional\VC\Tools\MSVC\14.29.30133\bin\Hostx64\x64\link.exe" /nologo CMakeFiles\template_specialization_conflict_test.dir\template_specialization_conflict_test.cpp.obj CMakeFiles\template_specialization_conflict_test.dir\main.cpp.obj  /out:template_specialization_conflict_test.exe /implib:template_specialization_conflict_test.lib /pdb:template_specialization_conflict_test.pdb /version:0.0 /machine:x64 /debug /INCREMENTAL /subsystem:console  kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib && cd ."
  LINK Pass 1: command "C:\PROGRA~2\Microsoft Visual Studio\2019\Professional\VC\Tools\MSVC\14.29.30133\bin\Hostx64\x64\link.exe /nologo CMakeFiles\template_specialization_conflict_test.dir\template_specialization_conflict_test.cpp.obj CMakeFiles\template_specialization_conflict_test.dir\main.cpp.obj /out:template_specialization_conflict_test.exe /implib:template_specialization_conflict_test.lib /pdb:template_specialization_conflict_test.pdb /version:0.0 /machine:x64 /debug /INCREMENTAL /subsystem:console kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib /MANIFEST /MANIFESTFILE:CMakeFiles\template_specialization_conflict_test.dir/intermediate.manifest CMakeFiles\template_specialization_conflict_test.dir/manifest.res" failed (exit code 1169) with the following output:
C:\Users\pc\source\repos\template_specialization_conflict_test\out\build\x64-Debug\main.cpp.obj : error LNK2005: "double __cdecl utils::my_template_function<double>(double)" (??$my_template_function@N@utils@@YANN@Z) already defined in template_specialization_conflict_test.cpp.obj
C:\Users\pc\source\repos\template_specialization_conflict_test\out\build\x64-Debug\template_specialization_conflict_test.exe : fatal error LNK1169: one or more multiply defined symbols found
  ninja: build stopped: subcommand failed.

Rebuild All failed.

我该如何解决这个问题？

Answer 1

我该如何解决这个问题？

您可以通过添加/使用关键字inline 来解决这个问题，这样专业化看起来像：

   //note the keyword inline in the below specialization
   template <> inline
    double my_template_function<double>(double parameter)
    {
        std::cout << "function specialization on double";
        std::cout << parameter;
        return parameter;
    }

这可以在here 中看到。

第二种解决此问题的方法是将您的专业化移动到源文件而不是标题中。所以你的 template_specialization_conflict_test.cpp 看起来像： template_specialization_conflict_test.cpp

#include "template_specialization_conflict_test.hpp"

namespace utils
{
    // Template Specialization
    //      A function specialized for double data type
    template <> 
    double my_template_function<double>(double parameter)
    {
        std::cout << "function specialization on double";
        std::cout << parameter;
        return parameter;
    }
}

该程序的工作原理如here 和here(with gcc and clang) 所示。