Visual C++ error LNK2019

Question

Okay, So I have always used the gcc compiler. This is my first project with this IDE. My project is organised like this:

main.cpp which includes a.h a.c which includes a.h and implements the methods declared in a.h

When I compiled it I get the following:

1>main.obj : error LNK2019: unresolved external symbol "void __cdecl destroyPlayer(struct player *)" (?destroyPlayer@@YAXPAUplayer@@@Z) referenced in function _main
1>main.obj : error LNK2019: unresolved external symbol "void __cdecl drawPlayer(struct player *)" (?drawPlayer@@YAXPAUplayer@@@Z) referenced in function _main
1>main.obj : error LNK2019: unresolved external symbol "void __cdecl movePlayer(struct player *,int *)" (?movePlayer@@YAXPAUplayer@@PAH@Z) referenced in function _main
1>main.obj : error LNK2019: unresolved external symbol "struct player * __cdecl createPlayer(int,int)" (?createPlayer@@YAPAUplayer@@HH@Z) referenced in function _main

These are all the functions in a.h. With the GCC command line I could compile them together. All files are added to the project. Am I missing something?

Solution 1

I believe Visual Studio automatically compiles .c files as C files, so name mangling could play a part in this. Try renaming a.c to a.cpp and see if it helps.

Solution 2

The error message is self-explanatory:

unresolved external symbol "void __cdecl destroyPlayer...

You have main.cpp and a.c.

For main.cpp linker expects that all functions declared in a.h use C++ name mangling and C++ calling convention, while for a.c linker expects that all functions declared in a.h use C naming and __cdecl calling convention.

If your code in a.c is not using C++ features, and you want to call it from main.cpp which does use C++ features, then in a.h you need to add the following:

#ifdef __cplusplus
extern "C" {
#endif

// your function declarations

#ifdef __cplusplus
}
#endif

Alternatively, if you don't need to mix C and C++, rename all the files to .c or to .cpp.

Finally, make sure that files are actually renamed because Visual Studio supports "virtual" rename (just in the project, without renaming the actual file).

Comments

[Laz]

named main and a to .cpp.. Doesnt help. So am I right in assuming that once a file is added to project, the compiler automatically includes it in the compilation process? AKA gcc main.c a.c -o whatever.. Or does it try to pull of some dll-ish stuff?

[Luchian Grigore]

@RamBhat yes, adding it to the project gets it compiled. It's probably something different. You can go to the project properties and see the exact command that's used to compile.

[john]

@RamBhat Try putting a deliberate error into a.c, just to check if it really is being compiled.

[Laz]

Tried adding an error. It doesnt compile error C2143: syntax error : missing ';' before '}'. So that proves a.c is going thru compilation.. This is a true linker issue ..

[Laz]

@Luchian Grigore Apologies for the noob question..Where in the project properties can I get the exact command..

[Luchian Grigore]

@RamBhat right click on project - properties - C++ - command line

[john]

When you renamed a.c to a.cpp did you force a rebuild? I see you've renamed it again. If it is C++ code it really should be a .cpp file.

[Laz]

@LuchianGrigore I had screwed up renaming a.c earlier(big noob moment).. My first comment can be ignored. You were right, thanks!