A: 

The warning, more probably than not, comes from the compiler. If you compiled and got the warning and later on removed it from the compilation process by means of a pragma or compiler option, it might be the case that the IDE still remembers it. It should go away in a later compilation, or you can manually delete within the Problems windows.

If you have not removed it from the compilation process (that is, the warning comes out in each new compilation) this will be mainly useless as the warning will come back. But then again, if it is still there, the IDE is just reminding you.

David Rodríguez - dribeas
@dribeas: no it doesn't go away if I recompile.
jldupont
@dribeas: how can you delete it from the "Problems" view? There is no option to do that.
jldupont
I am running eclipse cdt6, in the problems window if you select a line with a warning and right-click over it I have an option: delete (also accessible by pressing the 'delete' key). Eclipse warns you that until you recompile the code the error will not come back
David Rodríguez - dribeas
... I need to upgrade then! thanks!
jldupont