Unfamiliar code construct

Op Tue, 21 Jan 2014 13:34:40 +0100 schreef Bruce Varley :

If I read the C standard (n1570) right, then the expression is an lvalue of type void (implicitly) and shall be evaluated for its side effects. Accessing a volatile object is a side effect.

Bruce Varley schreef op 21-Jan-14 1:34 PM:

My guess is that SCISR1 is a macro for some register, something like

#define SCISR1 (*((volatile unsigned int *) 0x327F ))

that line with only SCISR1; would read the register a second time (the condition read it a first time). Maybe this is needed to clear the register or achieve some other side-effect. Check the documentation :)

Wouter van Ooijen

I prefer to write

(void) SCISR1;

in cases like this, to make explicit that the result is discarded.

Some of us prefer to write a COMMENT, such as // read SCISR1 to clear framoufoob bit, and discard the result

Aarrrggggg.....

No need to comment the obvious intention of the code. It's clear that the code is reading SCISR1, and that the result is discarded. So the comment can be:

(void) SCISR1; // clear framoufoob bit

Or even:

clear_framoufoob_bit( );

IMO it's useful information that framoufoob bit is cleared by reading the register.

So, nitpicking, the comment should be "reading SCISR1 clears framoufoob".

Oliver