[glideplan_swproj] Re: On library creating

  • From: Kuba Marek <blue.cube@xxxxxxxxx>
  • To: glideplan_swproj@xxxxxxxxxxxxx
  • Date: Thu, 5 Jan 2012 12:48:33 +0100

> I added directory Updraft/src/libraries and created new CMakeLists.txt
> The structure of the directory is same as in the case of plugins.
> Binaries are installed to the directory with executable.
> I also created skeleton of cup library, it can serve as an example.
> Please use the same structure for the new non-plugin libraries
> or write ideas how to changes if you are unsatisfied with this.

Maybe we should put everything into Updraft namespace.
::Updraft::Cup::CupLoader versus ::Cup::CupLoader ... 

Is it necessary to separate CupLoader from CupFile?

I prefer loading files from QIODevice to only specifying file name, or
QTextStream (Ales did it this way).
QIODevice has a lot of flexibility and it lets you do readLine.
(QTextStream also has readLine, but it also forces some character
encoding, because QStrings returned by it are in unicode)

> In rest of this message I wrote some words about libraries in general.
> When creating dynamic library you must export/import functions.
> I attach short how-to:
> I used following code for export/import macro in my header
> for cup files loading:
> #ifdef CUP_LIB
> #else
> #endif
> For proper functionallity it's necessary to add preprocessor definiton
> to the library project.
> Do this with CMake.
> For my library I added following line to the cup/CMakeLists.txt:

I think it's better to use some define that doesn't contain name of the
library (UPDRAFT_LIB_INTERNAL ?), because otherwise we won't be able to
just copy the CMakeLists.txt.

> I noticed that there is already defined cup_EXPORTS value.
> I googled it and found out that it is automatically added by cmake
> when creating dll. But there was written that it is done on Windows.
> If it works automatically also on Mac and Linux, ADD_DEFINITIONS
> can be omitted.
> If you want to link a library to some project, you must add
> TARGET_LINK_LIBRARIES command to the project's CMakeList.txt file.
> This command ensures the right build order and specify to import the
> lib. (There is probably some cmake code for Qt. If so, only add name
> of the desired library to the list in command.)
> Example...I linked cup library to the task_decl project with this
> line:
> May be you'll need to delete cache (build directory) to apply changes
> in the project.

Rerunning cmake should be enough, shouldn't it?

> ---Some words about import/export macro
> All the magic of the export/import macro is that
> when the header is included in other project than the library
> (typically executable project), there is not specified the CUP_LIB
> value so the import macro is used.
> As far as I know on the Windows happens this:
> When creating dll Visual Studio creates .dll file and also .lib file
> which serves as an import library. (When creating static lib, VS
> creates only .lib file which serves as the static library ...seems
> that .lib file can have two different meanings)
> When you use some imported functions (in project which uses the
> library), they are searched by linker in the import library
> (so the lib file must be available to the linker and known by it)
> Linker also add a notice to your binary telling that the function
> will be loaded at runtime from the appropriate dll (so the dll file
> must be available at runtime).
> Tom

I'll fix my library to fit the directory structure you created.


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