hi,
i would like to know difference between inline function and macro in c++. Given an option , which one should be used or given preference over the other???

Inline functions anytime win over Macros..atleast It gives you a chance of writing a better code(though no guarantees). macros are simply evil most of the time.

I agree with alcoholic, but the OP also asked for an explanation of the difference.

Observe this code, which uses a macro function and an inline function for the same purpose:
The difference is that the INC_X line will be converted by the preprocessor (before the compiler ever sees it) to "++(y)". The preprocessor does direct text substitution. The inc_x line, on the other hand, will be preserved as a function call, and will be inlined by the compiler. But since inc_x doesn't return its variable, it is useless and its argument will not be incremented. The fix for this, of course, is to use a reference, which is what inc_x_ref does. I hope this useless and convoluted code sample helps you understand the difference.

By the way, the nature of macros creates a huge number of headaches and potential gotchas, which I won't go into here, but they more than justify alcoholic's statement. You can find many rants about this on Google.