restructuring dependencies of some files in a project using precompiled headers causes linker errors

Question

I'm using MSVC++ 6 to build a very large project. Some of the source files in this project are shared with a small utility that we use for maintaining the application. Previously, this small utility required linking against many libs from the main app and also required the main app's DLLs at runtime. I was tasked with removing these dependencies, which sounded pretty simple... unfortunately, the precompiled headers used in the main app are causing me a lot of trouble.

I first reworked all the files in the utility to explicitly include everything they need and then I removed the #include directives for the PCH (this removed 95% of the unnecessary dependencies for the utility). This works great for compiling the utility. Now, however, compiling the main app gives me errors about missing precompiled header directives. I thought "great, I'll just conditionally include the PCH". This does not seem to work... I get "unexpected #endif", as mentioned here. My next thought was to turn off PCH in the main app for the three source files that are shared between the utilty and the main app. This compiles successfully, but I get a bunch of errors that look like this during linking:

tls7d.lib(tls707d.dll) : error LNK2005: "public: unsigned int __thiscall RWCString::length(void)const " (?length@RWCString@@QBEIXZ) already defined in stripledescypher.obj

AFAICT, all of the multiply defined symbols are ones that I explicitly include in the shared files to avoid the need for the PCH. My hunch is that since I'm linking those 3 files into the same DLL as the PCH .cpp file, they're compiled in multiple places. Is there any way out of this mess? I'll try just about anything...

Answer 1

When the compiler finds a definition of a symbol X when processing a compilation unit, it will create a hint for the linker: X is in here!

The compilation of two source files, both #includeing a header with a definition (i.e. not a mere declaration) will result in two object files defining the same symbol. The linker will find a symbol multiply defined.

So it appears that your stripledescypher object file includes a definition of the WCString::lenght()const method. This may be due to the function body being defined in the class' header or something the like.