On Mon, Nov 16, 2020 at 01:38:01PM +0000, Will J Godfrey wrote: > I just did a search of the whole of src. It's *used* about a dozen times > across 5 otherwise unrelated .cpp files, but is only defined here. Just to be > certain, I did a make clean before trying this again, and it's definitely > saying > multiple defs
As I understand things, extern int x; extern const int x; _declare_ x. That means it tells the compiler that x is _defined_ (as below) somewhere else. It does not create x. OTOH int x; int x = 123; const int x = 123; _define_ x. That means that a variable 'x' is created. If this is done at global scope (i.e. not inside a function or class), and there is more than one such definition, you should get a 'multiple definition' error from the linker. If there is no such definition, you should get an 'undefined' linker error if any compilation unit refers to x. So you should have _exactly_ one definition (this is why definitions should not be in a header file), and you can have as many declarations as needed. For things like your ADD_COLOUR, there are two approaches: * define and initialise it as a 'const int' in single compilation unit (e.g. globals.cpp), and declare it as external in a header file (e.g. globals.h) that gets included by all other compilation units that need it. or * Just #define it in a header (e.g. globals.h) instead of creating a variable. Ciao, -- FA _______________________________________________ Linux-audio-dev mailing list Linux-audio-dev@lists.linuxaudio.org https://lists.linuxaudio.org/listinfo/linux-audio-dev
