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From: samperi@marob.MASA.COM (Dominick Samperi)
Newsgroups: comp.lang.c++
Subject: Re: Fast Fourier Transformer in C++
Summary: Parametrized classes demo & bug
Message-ID: <479@marob.MASA.COM>
Date: 21 Jan 89 17:59:23 GMT
References: <518@cs-spool.calgary.UUCP> <6217@thorin.cs.unc.edu> <6250@thorin.cs.unc.edu>
Reply-To: samperi@marob.masa.com (Dominick Samperi)
Organization: ESCC  New York City
Lines: 205

In article <6250@thorin.cs.unc.edu> coggins@coggins.UUCP (Dr. James Coggins) writes:
>Seriously, I think we need a LOT more code examples posted to this
>newsgroup.  Not just demonstrations of errors, but real design
>examples. 

Well, this isn't a real design example, but it addresses an important C++
issue, namely, parametrized classes, implemented via the macro package
in <vector.h>. First, it illustrates that there are some rather messy
syntactical restrictions (no blanks in the macro formal parameter list,
macro expansion inside of comments, etc.), and second, it illustrates
that there are some other problems, leading to bugs when the macro
package is used (which is the case when BUG is defined). The bug is
described in counter::counter(counter& cnt).

Any insights would be appreciated.

Dominick Samperi
samperi@acf8.nyu.edu
uunet!hombre!samperi

/* #define BUG /* Uncomment this to use <vector.h> and cause a BUG! */

#include <stream.h>

#ifdef BUG 

#include <vector.h>

declare(vector,int) ;	// NOTE: no spaces allowed between () here!
implement(vector,int) ;	// NOTE: this macro should only be expanded in ONE file.
			//       ^^^^ can't say the implXXX word here, since
			//            the macro processor doesn't understand //!

#else

class vector {
	int *v ;
	int sz ;
public:
	vector(int) ;
	vector(vector&) ;
	~vector() ;
	int size()	{ return sz ; }
	int& operator[](int) ;
	vector operator=(vector) ;
} ;

vector::vector(int siz)
{
	sz = siz ;
	v = new int[sz] ;
}

vector::vector(vector& vv)
{
	sz = vv.size() ;
	v = new int[sz] ;
	for(int i = 0 ; i < sz ; i++) v[i] = vv[i] ;
}

vector::~vector()
{
	delete v ;
}

int& vector::operator[](int i)
{
	return v[i] ;
}

vector vector::operator=(vector vv)
{
	for(int i = 0 ; i < sz ; i++) v[i] = vv[i] ;
	return *this ;
}

#endif

class counter {
#ifdef BUG
	vector(int) *low, *high, *incr, *count ;
#else
	vector *low, *high, *incr, *count ;
#endif
	int sz ;
public:
#ifdef BUG
	counter(vector(int)&, vector(int)&, vector(int)&) ;
#else
	counter(vector&, vector&, vector&) ;
#endif
	counter(counter&) ;
	~counter() ;
	int size() { return low->size() ; }
	void reset()	{ *count = *low ; }
	void print() ;
	int operator[](int i)	{ return (*count)[i] ; }
} ;

void counter::print()
{
	cerr << "Counter(low,high,incr,count): \n" ;
	for(int i = 0 ; i < sz ; i++)
	{
		cerr << i << ": " << (*low)[i] << " " << (*high)[i] << " "
		     << (*incr)[i] << " " << (*count)[i] << "\n" ;
	}
}

#ifdef BUG
counter::counter(vector(int)& lo, vector(int)& hi, vector(int)& inc)
#else
counter::counter(vector& lo, vector& hi, vector& inc)
#endif
{
	sz = lo.size() ;
#ifdef BUG
	low = new vector(int)(sz) ;
	high = new vector(int)(sz) ;
	incr = new vector(int)(sz) ;
	count = new vector(int)(sz) ;
#else
	low = new vector(sz) ;
	high = new vector(sz) ;
	incr = new vector(sz) ;
	count = new vector(sz) ;
#endif
	*low = lo ;
	*high = hi ;
	*incr = inc ;
	*count = lo ;
}

counter::counter(counter& cnt)
{

cerr << "cnt param before instantiation:\n" ;
cnt.print() ;

	sz = cnt.size() ;
#ifdef BUG

/*
*  When BUG is defined, these memory allocation statements cause cnt to be
*  corrupted, as you will see from the output generated by cnt.print() before
*  and after this code.
*/

	low = new vector(int)(sz) ;
	high = new vector(int)(sz) ;
	incr = new vector(int)(sz) ;
	count = new vector(int)(sz) ;
#else
	low = new vector(sz) ;
	high = new vector(sz) ;
	incr = new vector(sz) ;
	count = new vector(sz) ;
#endif

cerr << "cnt after instantiation:\n" ;
cnt.print() ;

	*low = *cnt.low ;
	*high = *cnt.high ;
	*incr = *cnt.incr ;
	*count = *low ;
}

counter::~counter()
{
	delete count ;
	delete incr ;
	delete high ;
	delete low ;
}

ostream& operator<<(ostream& s, counter& c)
{
	s << "[ " ;
	for(int i = 0 ; i < c.size() ; i++)
		s << form("%2d", c[i]) << " " ;
	return s << "]\n" ;
}

main()
{
#ifdef BUG
	vector(int) low(3), high(3), incr(3) ;
#else
	vector low(3), high(3), incr(3) ;
#endif

	for(int i = 0 ; i < 3 ; i++)
	{
		low[i] =  1 ;
		high[i] = 5 ;
		incr[i] = 1 ;
	}

	counter select(low, high, incr) ;

	select.print() ;

	counter x = select ;
}