C++ and sizeof

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3 total messages Started by David Eppstein Fri, 17 Oct 1986 17:14

#356

Author: David Eppstein
Date: Fri, 17 Oct 1986 17:14

18 lines
1108 bytes

Is there a good reason why CC expands sizeof itself?  E.g. in

test.c:				test..c:
    struct x {			    struct x { /* sizeof = 8 */
	int a;			    int _x_a ;
	float b;		    float _x_b ;
    };				    } ;

    int foo(struct x y)		    int foo (_auto_y )struct x _auto_y ;
    {				    {
	return y.a + sizeof(y);	    return (_auto_y . _x_a + 8);
    }				    }

why does the  sizeof(y)  become  8  and not  sizeof(struct x)?
Is there some other use CC makes of the size that makes up for the
resulting lack of portability?
-- 
David Eppstein, eppstein@cs.columbia.edu, seismo!columbia!cs!eppstein

Re: C++ and sizeof

#363

Author: tk
Date: Sun, 19 Oct 1986 23:56

10 lines
1035 bytes

In article <3522@columbia.UUCP> eppstein@garfield.columbia.edu (David Eppstein) writes:
>Is there a good reason why CC expands sizeof itself?  E.g. in
> ...
>why does the  sizeof(y)  become  8  and not  sizeof(struct x)?
>Is there some other use CC makes of the size that makes up for the
>resulting lack of portability?

What lack of portability? If you're counting on the C++ translator to produce
"portable C" as its output I think you'll have problems since cfront uses
machine dependent size and alignment information.

Re: C++ and sizeof

#374

Author: Frank Adams
Date: Fri, 24 Oct 1986 19:22

20 lines
1659 bytes

In article <1772@clyde.ATT.COM> tk@moss.UUCP (Thomas Kirk) writes:
>In article <3522@columbia.UUCP> eppstein@garfield.columbia.edu (David Eppstein) writes:
>>Is there a good reason why CC expands sizeof itself?  E.g. in
>> ...
>>why does the  sizeof(y)  become  8  and not  sizeof(struct x)?
>>Is there some other use CC makes of the size that makes up for the
>>resulting lack of portability?
>
>What lack of portability? If you're counting on the C++ translator to produce
>"portable C" as its output I think you'll have problems since cfront uses
>machine dependent size and alignment information.

This fails to answer the question.  *What* does cfront use machine
dependant size and alignment information for?  Off hand, I can't think of
anything it does for which this information is necessary, although it is a
simplification to be able to carry around numbers instead of expressions for
sizes.

Frank Adams                           ihnp4!philabs!pwa-b!mmintl!franka
Multimate International    52 Oakland Ave North    E. Hartford, CT 06108

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