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From: jjk@jupiter.astro.umd.edu (Jim Klavetter)
Newsgroups: comp.lang.c
Subject: do I need to allocate space twice?
Message-ID: <8338@umd5.umd.edu>
Date: 29 Mar 91 22:03:41 GMT
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Reply-To: jjk@astro.umd.edu (Jim Klavetter)
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Organization: U of Md., Astronomy Program
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I have a function which returns a pointer of type double.  This is
really an "array".  Should the main program or the function allocate
the space?  Does it matter?  Certainly, I don't need to allocate space
twice, right?

To make this clear, here is a simple example:  add two arrays:

double *addarray(a, b, n)
double *a, *b;
int n;
{
	int i;
	double *result;

	for(i=0; i<n; i++)
		result[i]=a[i]+b[i];
	return(result);
}

with the main program having the fragment:

double *sum, *addarray();
...
sum=addarray(x, y, num);
...

The question is where do I allocate the storage for sum?  It seems to
me that if I do it in the function, then I can just return the pointer
and that is all, since the space will be allocated.  Is this correct?
As a followup, if I ever want to free the space, and it is true that I
allocate it in the function, then can I free the pointer from main?

As an aside, don't worry about code optomization or even bugs:  I just
made it up on the fly and I use it to get the idea across.  If I've
made any conceptual mistakes, on the other hand, please let me know?

jjk@astro.umd.edu also for Athabasca and Reudi
Jim Klavetter
Astronomy
UMD
College Park, MD  20742