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

Question

I get this error  but I don t know how to fix it  I m using Visual Studio 2013  I made the solution name MyProjectTest This is the structure of my test solution   -function h  ifndef MY FUNCTION H  define MY FUNCTION H  int multiple int x  int y    endif  -function cpp  include  quot function h quot   int multiple int x  int y       return x y     -main cpp  include  lt iostream gt   include  lt cstdlib gt   include  quot function h quot   using namespace std   int main        int a  b      cin  gt  gt  a  gt  gt  b      cout  lt  lt  multiple a  b   lt  lt  endl       system  quot pause quot        return 0     I m a beginner  this is a simple program and it runs without error  I read on the Internet and became interested in the unit test  so I created a test project  Menu File   New   Project      Installed   Templates   Visual C     Test   Native Unit Test Project   Name  UnitTest1  Solution  Add to solution Then the location auto-switched to the path of the current open solution  This is the folder structure of the solution   I only edited file unittest1 cpp   include  quot stdafx h quot   include  quot CppUnitTest h quot   include  quot    MyProjectTest function h quot   using namespace Microsoft  VisualStudio  CppUnitTestFramework   namespace UnitTest1       TEST CLASS UnitTest1            public           TEST METHOD TestEqual                        Assert  AreEqual multiple 2  3   6                  TODO  Your test code here                      But I get   error LNK2019  unresolved external symbol   I know that the implementation of function multiple is missing  I tried to delete the function cpp file and I replaced the declaration with the definition  and it ran  But writing both declaration and definition in the same file is not recommended  How can I fix this error without doing that  Should I replace it with  include  quot    MyProjectTest function cpp quot  in file unittest cpp

User · Answer

It turned out I was using  c files with  cpp files  Renaming  c to  cpp solved my problem

User · Answer

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

User · Answer

In the Visual Studio solution tree  right click on the project  UnitTest1   and then Add   Existing item   choose the file    MyProjectTest function cpp

User · Answer

Check the character set of both projects in Configuration Properties   General   Character Set  My UnitTest project was using the default character set Multi-Byte while my libraries were in Unicode  My function was using a TCHAR as a parameter  As a result  in my library my TCHAR was transformed into a WCHAR  but it was a char  in my UnitTest  the symbol was different because the parameters were really not the same in the end

User · Answer

I just discovered that LNK2019 occurs during compilation in Visual Studio 2015 if forgetting to provide a definition for a declared function inside a class  The linker error was highly cryptic  but I narrowed it down to what was missing by reading through the error and provided the definition outside the class to clear this up

User · Answer

In my case  set the cpp file to  quot C C   compiler quot  in  quot property quot - gt  quot general quot   resolve the LNK2019 error

User · Answer

Since I want my project to compile to a stand-alone EXE file  I linked the UnitTest project to the function obj file generated from function cpp and it works  Right click on the  UnitTest1  project   Configuration Properties   Linker   Input   Additional Dependencies   add  quot    MyProjectTest Debug function obj quot

User · Answer

I just ran into this problem in Visual Studio 2013   Apparently now  having two projects in the same solution and setting the the dependencies is not enough   You need to add a project reference between them   To do that    Right-click on the project in the solution explore Click Add    References    Click the Add New Reference button Check the boxes for the projects that this project relies on Click OK

User · Answer

For me it works if I add this line below in  vcxproj in the itemGroup cpp file  which is connected to the header file   lt ClCompile Include  quot file cpp quot    gt

User · Answer

Another way you can get this linker error  as I was  is if you are exporting an instance of a class from a DLL file  but have not declared that class itself as import export   ifdef  MYDLL EXPORTS     define DLLEXPORT   declspec dllexport   else     define DLLEXPORT   declspec dllimport   endif  class DLLEXPORT Book     lt --- This class must also be declared as export import       public          Book             Book            int WordCount        DLLEXPORT extern Book book      lt -- This is what I really wanted  to export book object  So even though primarily I was exporting just an instance of the Book class called book above  I had to declare the Book class as export import class as well otherwise calling book WordCount   in the other DLL file was causing a link error

User · Answer

In Visual Studio 2017 if you want to test public members  simply put your real project and test project in the same solution  and add a reference to your real project in the test project   See C   Unit Testing in Visual Studio from the MSDN blog for more details  You can also check Write unit tests for C C   in Visual Studio as well as Use the Microsoft Unit Testing Framework for C   in Visual Studio  the latter being if you need to test non public members and need to put the tests in the same project as your real code   Note that things you want to test will need to be exported using   declspec dllexport   See Exporting from a DLL Using   declspec dllexport  for more details

[c++] How can I solve the error LNK2019: unresolved external symbol - function?

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