Question

I,m using gcc compiler(MinGW) on Windows XP.I created a .dll library libdir.dll than I tried to build a program that is using that library.
I don’t want to put that .dll file into System or System32 folder nor to set path to it in PATH variable, what i want is to give that information to the program itself.
I know there is a -R and -rpath switches available so i was gonna link it with one of them.

First -rpath:
gcc -L/path/to/lib -Wl,-rpath,/path/to/lib main.o -ldir -o prog

Than -R:
gcc -L/path/to/lib -Wl,-R,/path/to/lib main.o -ldir -o prog

This links successfully into prog but when i start the program Windows prints message that it cannot find libdir.dll.
So my question is what went wrong, why path to libdir.dll is not known in runtime even when I’m using appropriate switches?

Let’s say i have prog1 and prog2 each containing their own copy of libdir.dll and both of them start to run at the same time loading code in the library.What happens in memory is there a two copies loaded or linker figures out that there is a copy and uses that for both programs?
Second question is about how libraries are loaded(any OS).Does linkers always load entire library or just parts needed?For example if program references function foo() which is in the library, does linker maps into memory only that function or entire library first?

Answer 1

There are only two real alternatives: put the DLL in the same folder as the EXE or put it in the working directory for the EXE. The latter being not much of an option since you’d have to create a shortcut to make the default working directory different from the directory that contains the EXE.

Not putting the DLL in the same directory as the EXE only makes sense if you want to share the DLL with other applications. To avoid the inevitable DLL hell this causes, you’d need to store the DLL in the side-by-side cache. The tooling you need to create the manifest and embed it in the EXE and the installer you’d need to deploy the DLL to the target machine are probably hard to come by with your tool chain. It is very rarely done anyway.