How to solve the 'error LNK2019' problem | Together C & C++ | Page 1

wooden finch Oct 17, 2022, 9:37 AM

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I met LNK2019, but I don't know how to solve it.

hollow mortarBOT Oct 17, 2022, 9:37 AM

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wooden finch Oct 17, 2022, 9:38 AM

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AimEM.obj : error LNK2019: 无法解析的外部符号 "struct ifr::Config::ConfigController __cdecl ifr::Config::createConfig<struct EM::AimEM::AimOffset>(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,struct EM::AimEM::AimOffset *,struct ifr::Config::ConfigInfo<struct EM::AimEM::AimOffset> const &)" (??$createConfig@UAimOffset@AimEM@EM@@@Config@ifr@@YA?AUConfigController@01@AEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@PEAUAimOffset@AimEM@EM@@AEBU?$ConfigInfo@UAimOffset@AimEM@EM@@@01@@Z)，函数 "public: __cdecl EM::AimEM::AimEM(bool)" (??0AimEM@EM@@QEAA@_N@Z) 中引用了该符号 [...\cmake-build-debug\XXX.vcxproj]
...\cmake-build-debug\Debug\XXX.exe : fatal error LNK1120: 1 个无法解析的外部命令 [...\cmake-build-debug\XXX.vcxproj]

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Declaration and implementation

template<class T>
 ConfigController createConfig(const std::string &name, T *data, const ConfigInfo<T> &info);

template<class T>
ConfigController createConfig(const std::string &name, T *data, const ConfigInfo<T> &info){
 //some code
}

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dire spear Oct 17, 2022, 9:41 AM

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are you putting template implementation in a source file instead of a header?

wooden finch Oct 17, 2022, 9:42 AM

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dire spear are you putting template implementation in a source file instead of a header?

I have written in both places.

dire spear Oct 17, 2022, 9:42 AM

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typically template needs to be in header file, refer to this, https://stackoverflow.com/questions/115703/storing-c-template-function-definitions-in-a-cpp-file

Stack Overflow

Storing C++ template function definitions in a .CPP file

I have some template code that I would prefer to have stored in a CPP file instead of inline in the header. I know this can be done as long as you know which template types will be used. For exam...

wooden finch Oct 17, 2022, 9:44 AM

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delicate creek Oct 17, 2022, 9:45 AM

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I had this problem when I was compiling my project with clang, but linking with ld and not lld

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check your linker settings and see if you're mixing g++ and clang

wooden finch Oct 17, 2022, 9:54 AM

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Hmm, I'm sorry. I don't know where to check. I use Clion, maybe this ?

dire spear Oct 17, 2022, 10:00 AM

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did you try what I suggested?

wooden finch Oct 17, 2022, 10:05 AM

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#ifndef IFR_OPENCV_CONFIG_HPP
#define IFR_OPENCV_CONFIG_HPP

namespace ifr {
    namespace Config {        
        struct ConfigController {
            std::function<void()> save;//save config
            std::function<void()> load;//load config
        };

        template<class T>
        struct ConfigInfo {
            std::function<void(T *, rapidjson::Writer<StringBuffer> &)> serialize;
            std::function<void(T *, const rapidjson::Document &)> deserialization;
        };

        template<class T>
        ConfigController createConfig(const std::string &name, T *data, const ConfigInfo<T> &info);
    };
} // ifr

#endif //IFR_OPENCV_CONFIG_HPP

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My header file is similar to this. It is different from that in the link. It is not a class

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😭

delicate creek Oct 17, 2022, 11:23 AM

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Since youre not really giving enough information I'd just start commenting stuff out untill it compiles and then start adding stuff back to see exactly where compilation fails.

wooden finch Oct 17, 2022, 12:03 PM

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Well, I finally understand that it seems that my current compiler (C++14) cannot separate the declaration and implementation of template functions unless I use C++20.

hollow mortarBOT Oct 17, 2022, 12:04 PM

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Thank you and let us know if you have any more questions!

#How to solve the 'error LNK2019' problem