Thanks. Now I see the meaning of -DBUILD_DLL.
Would you please tell me how to find the content of the macro BUILD_DLL in Codeblocks? I am new to Codeblocks. So my question perhaps is naive. Sorry about that.
This has nothing to do with codeblocks... Codeblocks is a text editor. It does only what you tell it to do. So somewhere in the project you (or some template) told the compiler to define BUILD_DLL... What the library you use does with it has nothing to do with codeblocks... It is probably used by your standard library, or some unused legacy thing...
EDIT:
there is no content of BUILD_DLL ... this simply is used in code like this
#ifdef BUILD_DLL
do something
#else
do something else
#endif