Path: utzoo!mnetor!uunet!husc6!mailrus!umix!umich!mibte!gamma!sabre!faline!scherzo!allegra!alice!shopiro
From: shopiro@alice.UUCP
Newsgroups: comp.lang.c++
Subject: Re: resizing operator
Message-ID: <7708@alice.UUCP>
Date: 19 Feb 88 03:44:36 GMT
References: <24568@cca.CCA.COM>
Organization: AT&T Bell Laboratories, Murray Hill NJ
Lines: 51
Summary: it is easy to build custom resizing into vector classes

In article <24568@cca.CCA.COM>, alex@cca.UUCP writes:
> 
> One of the language features that I find missing in C++ is some built-in
> support for vector allocation resizing, such as a resize operator.  Many
> of my programs make use of dynamically changing allocations.  When they
> were written in C, realloc was used.  It is possible to specify the memory
> allocation function for new and delete, which (presumably) would allow one
> to implement a realloc-type function.  But it would be a cleaner interface
> to have language support, probably like
> 
> 	resize[count] pointer;
> 
> which would be similar to vector delete.
> 
> Has any thought been given to this area?  Am I missing something obvious?

Since C++ per se has a rather weak notion of vectors, it would be
difficult to provide a general vector resizing operator as part
of the language.  It is easy, however, for the programmer to
write a vector datatype with a resizing operation.

For example, you might write code like the following

class Int_vec {
	int*	data;
	int	size;
public:
	Int_vec(int s) { data = new int[size = s]; }
	~Int_vec() { delete [size] data; }
	int&	operator[](int i) { return data[i]; }  // add bounds check s.v.p.
	void	resize(int);
};

void
Int_vec::resize(int new_size)
{
	int*	p = new int[new_size];
	for (register int i = min(size, new_size); i--; )
		p[i] = data[i];
	free [size] data;
	data = p;
	size = new_size;
}

Alternatively, you could supply Int_vec with operator new() and
operator delete() with definitions that called malloc() and free(),
and then you could use realloc() in Int_vec::resize().
-- 
		Jonathan Shopiro
		AT&T Bell Laboratories, Murray Hill, NJ  07974
		research!shopiro   (201) 582-4179