I have a C library A with no test and I am trying to add tests for one of its functions funC:

in funC is not declared in A/lib.h and only declared in A/lib.c:

static int funC();

static int funC(){
    // do something
}

and I created a test file in test/A.t.cpp and want to access funC to test it. funC is only declared in .c file so i decide to use extern C. in test/A.t.cpp I have:

extern "C"{
    static int funC();
}

TEST(A,test){
    funC();
    .....
}

I thought with the declaration in the .t.cpp file, it would be able to link against the actual implementation in the .c file so I should be able to call the function and test it, but I got:

Error: The function funC() has not had a body defined

how should I fix it? Then I also tried to add the implementation within the test file and it worked but that's not what I want. I want the .t.cpp file to link against the actual implementation in .c file. Thanks!

CodePudding user response：

Your function funC() has internal linkage (this is the meaning of static for functions and file-scope variables in C). It cannot be called by name from other translation units than the one it is defined in, whether C or C .

In your test source, the same name refers to a different function, for which you have not provided a definition.

If you want funC() to be callable from your separate test file then you should change it to have external linkage by removing its static qualifier or changing it to extern. You will need to make the same change to the declaration in the test file.

CodePudding user response：

To unit test static functions, this is one of the rare cases where you would need to include a .c file:

extern "C"{

#include "A/lib.c"

}

TEST(A,test){
    funC();
    .....
}

Then the static functions and variables will be visible in the test code.