[glideplan_swproj] On library creating

  • From: Tomáš Zámečník <pulcik@xxxxxxxx>
  • To: glideplan_swproj@xxxxxxxxxxxxx
  • Date: Thu, 05 Jan 2012 12:27:58 +0100 (CET)

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.

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

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 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 
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 

---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 
...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).


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