Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ukma!rutgers!att!cbnewsl!dfp
From: dfp@cbnewsl.ATT.COM (david.f.prosser)
Newsgroups: comp.lang.c++
Subject: Re: initializing array of objects
Message-ID: <885@cbnewsl.ATT.COM>
Date: 22 Jun 89 17:56:38 GMT
References: <1284@cadillac.CAD.MCC.COM> <1000015@hpclscu.HP.COM>
Reply-To: dfp@cbnewsl.ATT.COM (david.f.prosser)
Organization: AT&T Bell Laboratories
Lines: 39

In article <1000015@hpclscu.HP.COM> shankar@hpclscu.HP.COM (Shankar Unni) writes:
>> bright@Data-IO.COM (Walter Bright) writes:
>> 
>> Try:
>> 	memset(fooArray,0,100 * sizeof(fooArray[0]));
>> or:
>> 	fooArray = (Foo**) calloc(100,sizeof(fooArray[0]));
>> Both are faster and generate less code.
>
>And both are non-portable.
>
>Try the following:
>
>   memset (fooArray, (Foo *) 0, 100*sizeof(Foo *));
>
>It's fast and correct.
>----
>Shankar Unni.

Sorry.  Your example is no better than the first use of memset().  The
function sets *bytes* to the value of the middle argument.  Unless the
machine uses the same value for each byte of a pointer, this won't work.

Try:
	static const Foo *empty[100];
	(void)memcpy(fooArray, empty, sizeof empty);
or
	static const struct foo100struct { Foo *array[100]; } empty;
	foo100struct *p;
	p = new foo100struct;
	*p = empty;
	fooArray = p->array;

Both of these suffer from fixed sizes and both rely on the default
initialization of pointers to null.

(Apologies for any C++ usage errors; I am in no way an expert.)

Dave Prosser