error LNK2001: Linking error with VS C++ 6.0

[Wizard1981]

When building my project, I'm getting following error:

Test1Dlg.obj : error LNK2001: unresolved external symbol "int __cdecl get_contact_state(enum CONTACT)" (?get_contact_state@@YAHW4CONTACT@@@Z)
Debug/Test1.exe : fatal error LNK1120: 1 unresolved externals

I have included the function by it's header in Test1Dlg.cpp so it should work. There is no error if I dont call the function.
The directory of the header file is known to the project, the other files would link without any problem.

Any idea what could be the problem would be helpful!

[JosAH]

When building my project, I'm getting following error:

Test1Dlg.obj : error LNK2001: unresolved external symbol "int __cdecl get_contact_state(enum CONTACT)" (?get_contact_state@@YAHW4CONTACT@@@Z)
Debug/Test1.exe : fatal error LNK1120: 1 unresolved externals

I have included the function by it's header in Test1Dlg.cpp so it should work. There is no error if I dont call the function.
The directory of the header file is known to the project, the other files would link without any problem.

Any idea what could be the problem would be helpful!

Mentioning that function's prototype available just keeps the compiler's mouth shut.
There's still no guarantee though whether or not a compiled version of that function
exists and you have to make that compiled version available to the linker.

You didn't do that so the linker opened its mouth. If that function is stored in a
library you have to feed that library to the linker, otherwise if the compiled function
is just available in its own .o or .obj file you should feed that to the linker.

kind regards,

Jos

[oler1s]

The header allows the program to compile. You are getting a linker error, which means you forgot to link the library in. You need to specify the library directory and the actual library that gets linked in.

[Wizard1981]

Thx for your help so far!
The function is NOT available via a library but as a obj-File located in the same dir than its header. Thats why Im expecting the linker to find it. Actually, all obj-Files are in the Debug-Folder where the compiler put them.

[oler1s]

The function is NOT available via a library but as a obj-File located in the same dir than its header. Thats why Im expecting the linker to find it.

Header files aren't compiled. Only source files are. Besides, the include directories and source file directories are not relevant to the linker. Only where the intermediate and linkage time files are. If it so happens that they are in the same folder as the header or source files, well, ok.

Actually, all obj-Files are in the Debug-Folder where the compiler put them.

Object files? As in get_contact_state is a function you wrote? Did you properly write up the code in a source file, as opposed to merely declaring the existence of such a function?

[Wizard1981]

Did you properly write up the code in a source file, as opposed to merely declaring the existence of such a function?

Sure. I declared the function in a header, defined it in a source and included the header in the source-File using it (Test1Dlg). I compiled the source of the function independently with success so its obj-File is available in the Debug-Folder.

[Banfa]

I compiled the source of the function independently with success so its obj-File is available in the Debug-Folder.

Independently? You mean outside of your normal project? If this is the case them the object will not be included on the link command which is why the symbol is unresolved, the linker can not find it in the objects and libraries it is linking.

You will have to either change the project linker settings to include the object as an input to the linker or add the C file to your project so that it just gets compiled and linked when you build the project normally.

[JosAH]

Thats why Im expecting the linker to find it.

A linker doesn't go hunting for the needed files. You have to explicitly supply it
with the files you want to have linked together. IDEs might hide this fact a bit
by doing it for you but linkers have other things to do; they don't hunt for, nor
find files for you.

kind regards,

Jos

[Wizard1981]

Maybe I should have mentioned that I wanted to link obj-Files compiled from c-sources... Now that I renamed all c-Files to cpp everything workes fine :)
Thank you anyway!

[JosAH]

Maybe I should have mentioned that I wanted to link obj-Files compiled from c-sources... Now that I renamed all c-Files to cpp everything workes fine :)
Thank you anyway!

Oh great. Next time please supply correct and sufficient information along with
your question. This forum is not for guessing games.

kind regards,

Jos

[Wizard1981]

Unfortunately, often it IS the problem to know which information is relevant and which not. If I guessed that the problem is with the c-Files, I propably had not posted this problem

[weaknessforcats]

Maybe I should have mentioned that I wanted to link obj-Files compiled from c-sources... Now that I renamed all c-Files to cpp everything workes fine :)
Thank you anyway!

This is not what you do to get C object files in your executable.

If you have the source code, add the .c files to your project as .c files. Do not make a copy of the code. Add the files from the locations where they normally reside. .c files are compiled as C and .cpp files are compiled as C++.

C++ is not C. By renaming, something that compiled in C may no longer compile in C++ and if you fix it to compile in C++ it may no longer compile in C.

[Wizard1981]

That is exactly what I wanted to do. But as I now know, obj-Files compiled from c are not compatible with cpp. You have to tell the compiler that you want to use a function defined in c explicitly.
Anyway, I'm just using quite basic c which should be compilable by an cpp compiler.

[Banfa]

You have to tell the compiler that you want to use a function defined in c explicitly.

Yes but it isn't very hard to put

#ifdef __cplusplus
extern "C" {              /* Declare declarations as C in a C++ file  */
#endif  /* __cplusplus */
 
/* Function prototypes etc */
 
#ifdef __cplusplus
}
#endif  /* __cplusplus */
 
 

in your header file