C Interview Questions and Answers

 

Are pointers really faster than arrays?

Are pointers really faster than arrays? How much do function calls slow things down?
Is ++i faster than i = i + 1?





Precise answers to these and many similar questions depend of course on the processor
and compiler in use. If you simply must know, you'll have to time test programs
carefully. (Often the differences are so slight that hundreds of thousands of iterations
are required even to see them.



For conventional machines, it is usually faster to march through large arrays with
pointers rather than array subscripts, but for some processors the reverse is true.
(Better compilers should generate good code regardless of which notation you use,
though it's arguably easier for a compiler to convert array indices to pointers
than vice versa .)



Function calls, though obviously incrementally slower than in-line code, contribute
so much to modularity and code clarity that there is rarely good reason to avoid
them. (Actually, by reducing bulk, functions can improve performance.) Also, some
compilers are able to expand small, critical-path functions in-line, either as an
optimization or at the programmer's request.



Before rearranging expressions such as i = i + 1, remember that you are dealing
with a compiler, not a keystroke-programmable calculator. Any decent compiler will
generate identical code for ++i, i += 1, and i = i + 1. The reasons for using ++i
or i += 1 over i = i + 1 have to do with style, not efficiency.

Posted by:Richards