Error Lnk2019 Unresolved External Symbol

How can I solve the error LNK2019: unresolved external symbol - function?

One option would be to include function.cpp in your UnitTest1 project, but that may not be the most ideal solution structure. The short answer to your problem is that when building your UnitTest1 project, the compiler and linker have no idea that function.cpp exists, and also have nothing to link that contains a definition of multiple. A way to fix this is making use of linking libraries.

Since your unit tests are in a different project, I'm assuming your intention is to make that project a standalone unit-testing program. With the functions you are testing located in another project, it's possible to build that project to either a dynamically or statically linked library. Static libraries are linked to other programs at build time, and have the extension .lib, and dynamic libraries are linked at runtime, and have the extension .dll. For my answer I'll prefer static libraries.

You can turn your first program into a static library by changing it in the projects properties. There should be an option under the General tab where the project is set to build to an executable (.exe). You can change this to .lib. The .lib file will build to the same place as the .exe.

In your UnitTest1 project, you can go to its properties, and under the Linker tab in the category Additional Library Directories, add the path to which MyProjectTest builds. Then, for Additional Dependencies under the Linker - Input tab, add the name of your static library, most likely MyProjectTest.lib.

That should allow your project to build. Note that by doing this, MyProjectTest will not be a standalone executable program unless you change its build properties as needed, which would be less than ideal.

LNK2019: unresolved external symbol error in Visual Studio C++

'unresolved external symbol' means that you're not linking with required library.
Go to Properties -> Linker -> Additional Library dependencies and add path to OpenCV libs.

Unresolved external symbol in object files

This error often means that some function has a declaration, but not a definition.

Example:

// A.hpp
class A
{
public:
  void myFunc(); // Function declaration
};

// A.cpp

// Function definition
void A::myFunc()
{
  // do stuff
}

In your case, the definition cannot be found. The issue could be that you are including a header file, which brings in some function declarations, but you either:

1. do not define the functions in your cpp file (if you wrote this code yourself)
2. do not include the lib/dll file that contains the definitions

A common mistake is that you define a function as a standalone and forget the class selector, e.g. A::, in your .cpp file:

Wrong: void myFunc() { /* do stuff */ }
Right: void A::myFunc() { /* do stuff */ }

How do I fix error LNK2019: unresolved external symbol _glfwInit

First I had to install the windows 10 SDK
Then I had to change my vcvarsall in path to the VS2022 one
Then I had to run the vcvarsall x64
Then I had to remove the glfw3.lib in favor of the glfw3_mt.lib
Then I had to add the vulkan-1.lib to my lib/ directory
And finally it compiled and showed a window

LNK2019 Unresolved external symbol OOP and polymorphism?

Since you didn't post your code, I can only guess. If you are implementing your stack using a template (very common) then you may see this error if you define your template functions/methods in a separate .cpp file. Typically template functions & classes are defined inline or contain their definitions within the same header file as their declarations.

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