OFten i see programs starting with preprocessor directives such as #ifdef and ifndef and #define and etc and etc........
BUt i don't understand one thing. #ifdef is followed by a constants or words, or watever u call it ( e.g. NDEBUG ). And many of these hav underscores or 2 underscores in between the word(s), in front, or after it. WHY ?
Where are these 'words' defined? Where can i find out which 'words' are available? What do the underscores mean?
pls explain, i think this topic is very important.
thnx in advance