extern functions in header file

[Eljay Love-Jensen]

Hi Ming-Chia,

 >Is there any difference between declaring functions with prefix "extern" 
and without "extern" keyword in header files?

 From a C++ vantage point...

Effectively (by and large), no there's no difference.

Philosophically, yes.  Some consider (including myself) that supplying the 
(optional) <code>extern</code> keyword is good practice because it is 
self-documenting code.

Also, be aware that <code>extern "C"</code> has several important 
(critical!) implications regarding C++ code.

Also, in some areas, <code>extern</code> is REQUIRED to distinguish 
something that is "just a declaration" from being mistaken for a 
"definition" (without having the <code>extern</code>).  See Stroustrup's 
C++ Programming Language (3rd or special edition) section 9.2.

I haven't done C work since 1990, so my comments may not be appropriate for 
C "good style / best practices".

HTH,
--Eljay