> HOw can we add header files to a compiler (for example codevision)?
Generally speaking, you should not add header files to the set supplied by the compiler vendor unless you know exactly what you are doing.
> And can we add the header files of a compiler to other
> compiler (for example adding the header files of winAVR
> to codevision)?
Again, generally speaking, you should not intermix the header files supplied by compiler vendors unless you know exactly what you are doing.
On the other hand, you can create your own header files or use existing header files either by placing them in the same directory as the .c files which use them or by placing them in another directory and then modifying the compiler invocation commands to direct the compiler to look in one or more other directories for referenced include files.
If you are a novice, you are probably best advised to just place include files in the same directory as your .c source files.
Don Kinzer
ZBasic Microcontrollers
http://www.zbasic.net