Thread: Finding object code

Hi, I am relatively new to C and C++ (~2 months), having previously done all my programming in Object Pascal. My question is this: How does the linker know where to find object code for functions prototyped in header files?

In Object Pascal, the functions would either be DEFINED in a file, either in OP code, or in assembler (e.g. the writeln function, which outputs text to a console, is found in the writestr.asm file in the include directory), or the relevant DLL would be specified, e.g.

Code:

function SomeFunction; external 'somedll.dll' name 'whatever';

to include a function which is called whatever in somedll.dll and call it SomeFunction in the header file. However with C, there appears to be no such methodology. If I look at the header files, e.g. stdio.h, I just find lists and lists of prototypes, with no reference to object code.

My question arises because I am using a non-standard header file called conio.h. I use Dev-C++ and it provides a source file conio.c, but I have to compile it myself (to e.g. conio.o), and then pass the linker the path to the object code which I have compiled everytime I wish to run my program.

Now, there must be an easier way to do this. Surely the linker has some kind of search path where it looks for the object code, and surely SOMEWHERE there must BE object code for things like printf? And how does the compiler know for the functions in windows.h which DLL it has to look in to find, e.g. CreateWindow?

It would be helpful if someone could either help me on this or point me somewhere I could find more info, since the book I am using does not appear to cover it.

Thanks in advance,

Adam.

Originally Posted by itsme86

The methodology is compiler/linker specific, so I'm not surprised it's not covered in your C book. In Dev-C++ you can go to Tools -> Compiler Options, click the Directories tab and then go to the Libraries subsection. You can add another library directory there, but Dev-C++ won't automatically link that library when you compile each project. I haven't looked to see if you can change the call that Dev-C++ to the linker to include another library, but you can specify which libraries get linked in with each project. Check Dev-C++'s help for "Linking libraries with your project."

I went to the directory and found loads of .a files. Presumably these are similar in format to the .o files? Are they the same?

Also, the DLLs were not in the directory, and their location was not specified in windows.h. Does this mean that, for example, if I downloaded a new version of user32.dll, new programs compiled with Dev-C++ would not use the new code?

This .a files are libraries ( collection of .o files ). In C++ you alwais link libraries or object-files (.o).

Also, the DLLs were not in the directory, and their location was not specified in windows.h. Does this mean that, for example, if I downloaded a new version of user32.dll, new programs compiled with Dev-C++ would not use the new code?

As I said above the c++ linker alwais links against libraries, you do not directly link against .dll's. Some of this .a libraries are importlibraries. This libraries contain only stubs that do the actual calling of the functions in the dll's.
In Windows the dlls' are normally stored in some system directory and windows has its own system to find them when LoadLibrary() is called (this is done by the .a-files ).
So yes normally if you install some new dll then it will be used by your program.
If there are major changes in the dll's like added functions then the importlibraries have to be regenerated and you will have to install new versions of the headers as well.
Kurt