The compilation process

Question

Can anyone explain how compilation works?

I can\'t seem to figure out how compilation works..

To be more specific, here\'s an example.. I\'m trying to write some c

Answer 1

The two main steps are compilation and linking.

Compilation takes single compilation units (those are simply source files, with all the headers they include), and create object files. Now, in those object files, there are a lot of functions (and other stuff, like static data) defined at specific locations (addresses). In the next step, linking, a bit of extra information about these functions is also needed: their names. So these are also stored. A single object file can reference functions (because it wants to call them when to code is run) that are actually in other object files, but since we are dealing with a single object file here, only symbolic references (their 'names') to those other functions are stored in the object file.

Next comes linking (let's restrict ourselves to static linking here). Linking is where the object files that were created in the first step (either directly, or after they have been thrown together into a .lib file) are taken together and an executable is created. In the linking step, all those symbolic references from one object file or lib to another are resolved (if they can be), by looking up the names in the correct object, finding the address of the function, and putting the addresses in the right place.

Now, to explain something about the 'extern "C"' thing you need:

C does not have function overloading. A function is always recognizable by its name. Therefore, when you compile code as C code, only the real name of the function is stored in the object file.

C++, however, has something called 'function / method overloading'. This means that the name of a function is no longer enough to identify it. C++ compilers therefore create 'names' for functions that include the prototypes of the function (since the name plus the prototype will uniquely identify a function). This is known as 'name mangling'.

The 'extern "C"' specification is needed when you want to use a library that has been compiled as 'C' code (for example, the pre-compiled Lua binaries) from a C++ project.

For your exact problem: if it still does not work, these hints might help: * have the Lua binaries been compiled with the same version of VC++? * can you simply compile Lua yourself, either within your VC solution, or as a separate project as C++ code? * are you sure you have all the 'extern "C"' things correct?