Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!edcastle!elee24
From: elee24@castle.ed.ac.uk (H Bruce)
Newsgroups: comp.lang.c
Subject: Order of evalution of expressions.
Message-ID: <6398@castle.ed.ac.uk>
Date: 18 Sep 90 16:55:09 GMT
Organization: Dept. Electrical Engineering, Edinburgh University, Scotland, UK.
Lines: 21

I have lost my FAQ files but I'm certain this is not on it....

Is the line

value = *ptr - *ptr++;

sensible C ?
In other words is there a specified order of evaluation of expressions ?
If not then the answer would depend on when the increment is done.

If not what is the fastest way of computing this type of expression ?
Would the following lines be optimized by a compiler (so that value is
not loaded twice) ?

value = *ptr;
value -= *ptr++;


Thanks,

Henry Bruce.