error LNK: unresolved external symbol, resulting from virtual functions - visual-c++

Question

Following are the errors when I compile my code. I am sorry that I cannot share my code here. FYI, I don't use any externals libs, so I am really not sure about these linker errors. They seem to come from the virtual functions I declared in DeviceManager class. Their respective implementations are in two other classes.
Could someone help me out with these errors?
1>device_manager.obj : error LNK2028: unresolved token (0A000397) "public: virtual void __clrcall DeviceManager::loadConfig(class System::IO::StreamReader ^)" (?DeviceManager#DeviceManager##$$FUAMXP$AAVStreamReader#IO#System###Z) referenced in function "void __clrcall `dynamic initializer for 'const DeviceManager::`vftable'''(void)" (???__E??_7DeviceManager##6B###YMXXZ#?A0xc2524ebc##$$FYMXXZ)
1>device_manager.obj : error LNK2019: unresolved external symbol "public: virtual void __clrcall DeviceManager::loadConfig(class System::IO::StreamReader ^)" (?loadConfig#DeviceManager##$$FUAMXP$AAVStreamReader#IO#System###Z) referenced in function "void __clrcall `dynamic initializer for 'const DeviceManager::`vftable'''(void)" (???__E??_7DeviceManager##6B###YMXXZ#?A0xc2524ebc##$$FYMXXZ)
1>device_manager.obj : error LNK2001: unresolved external symbol "public: virtual class Device * __thiscall DeviceManager::createDevice(void)" (?createDevice#DeviceManager##UAEPAVDevice##XZ)
1>device_manager.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall DeviceManager::initializeDevices(void)" (?initializeDevices#DeviceManager##UAEXXZ)
1>C:\Users\CH\Documents\Visual Studio 2010\Projects\Test Devices\Test Devices\Debug\Test Devices.exe : fatal error LNK1120: 4 unresolved externals
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1>Build FAILED.
1>
1>Time Elapsed 00:00:01.50
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
Update 1 (Possible Solution):
The problem seems to be because of the virtual function(s) declared in DeviceManagerclass not being pure virtual and not having definition(s) in the .cpp of DeviceManager class.
If the DeviceManagerclass does not have any non-virtual function(s), then making the virtual function(s) pure will be the solution. Something like this virtual void testFunction(); is not pure, so changing it to virtual void testFunction()=0; is the solution. For this, it is enough to have the definition(s) of this virtual function implemented in other classe(s) that inherit the DeviceManager class. In such a case, the DeviceManagerclass becomes abstract and therefore cannot be instantiated.
But in my case, the DeviceManagerclass has some non-virtual functions as well and also needs to be instantiated to call the non-virtual functions. Therefore, the solution is to implement the definitions of the virtual functions in the .cpp of the DeviceManagerclass apart from declarations and definitions in other classes that inherit the DeviceManager class.

Answer 1

Have you tried a full clean and rebuild?
Does your class have at least one non virtual member function?
I have seen that issue a few years ago.
Other than that I suggest copying the function prototype and full parameter list out into word pad or something and changing the font (to stop it looking so familiar that your eyes scan over it) and then comparing every call to every function to make sure that they match up(more likely to cause a complile problem but is worth checking).