Exercise 10.3 exec_bad_access error

[TheWatchfulOne]

Code: (Objective-C)

//
//  Fraction.h
//  Program 9.2, Exercise 9.3, Exercise 9.4, Exercise 9.5, Program 10.1, Program 10.2
//
//  Created by anon on 5/31/10.
//  Copyright 2010 __MyCompanyName__. All rights reserved.
//

#import <Cocoa/Cocoa.h>
#import <objc/Object.h>

@interface Fraction : NSObject
{
	int numerator;
	int denominator;
}

// initializer methods

-(Fraction *) initWith: (int) n Over: (int) d;

//  setter methods

-(void) setNumerator: (int) n;
-(void) setDenominator: (int) d;
-(void) setTo: (int) n over: (int) d;

//  getter methods

-(int) getNumerator;
-(int) getDenominator;

//  other methods
-(double) convertToNum;
-(id) addValue: (id) f;
-(void) reduce;
-(void) print;

// allocation methods

+(Fraction *) allocF;
-(void) releaseF;
+(int) getCount;
+(int) getAddCount;
+(void) printCount;

@end

Code: (Objective-C)

//
//  Fraction.m
//  Program 9.2, Exercise 9.3, Exercise 9.4, Exercise 9.5, Program 10.1, Program 10.2
//
//  Created by anon on 5/31/10.
//  Copyright 2010 __MyCompanyName__. All rights reserved.
//

#import "Fraction.h"
#import <stdio.h>

static int gCounter;
static int gAddCount;

@implementation Fraction;

//  initializer methods

-(Fraction *) initWith:(int)n Over:(int)d
{
	self = [super init];
	
	if (self)
	{
		[self setTo: n over: d];
	}
	
	return self;
}

//  setter methods

-(void) setNumerator: (int) n
{
	numerator = n;
}

-(void) setDenominator: (int) d
{
	denominator = d;
}

//  getter methods

-(int) getNumerator
{
	return numerator;
}

-(int) getDenominator
{
	return denominator;
}

//  other methods

-(double) convertToNum
{
	if (denominator != 0)
		return (double) numerator / denominator;
	else
		return 0.0;
}

-(void) setTo: (int) n over: (int) d
{
	numerator = n;
	denominator = d;
}



-(id) addValue: (id) f   //add a Fraction to the receiver
{
	extern int gAddCount;
	++gAddCount;
	
	//to add two fractions:
	// a/b + c/d = ((a*d) + (b*c)) / (b*d)
	
	//result will store the result of the addition
	
	id resultFrac = [[Fraction alloc] init];
	int resultNum, resultDenom;
	
	resultNum = (numerator * [f getDenominator]) + (denominator * [f getNumerator]);
	resultDenom = denominator * [f getDenominator];
	
	[resultFrac setTo: resultNum over: resultDenom];
	[resultFrac reduce];
	
	return resultFrac;
}

-(void) reduce
{
	int u = numerator;
	int v = denominator;
	int temp;
	
	while ( v != 0 )
	{
		temp = u % v;
		u = v;
		v = temp;
	}
	
	numerator /= u;
	denominator /= u;
}

-(void) print
{
	printf(" %i/%i ", numerator, denominator);
}

// allocation methods

+(Fraction *) allocF
{
	extern int gCounter;
	++gCounter;
	
	return [Fraction alloc];
}

-(void) releaseF
{
	extern int gCounter;
	--gCounter;
	
	[self release];
}

+(int) getCount
{
	extern int gCounter;
	
	return gCounter;
}

+(int) getAddCount
{
	extern int gAddCount;
	
	return gAddCount;
}

+(void) printCount
{
	extern int gCounter;
	
	printf("%i Fractions are declared.\n", gCounter);
}

@end

Code: (Objective-C)

//
//  main.m
//  Exercise 10.3
//
//  Created by anon on 7/3/10.
//  Copyright 2010 __MyCompanyName__. All rights reserved.
//

#import <Cocoa/Cocoa.h>
#import "Fraction.h"

int main(int argc, char *argv[])
{
	Fraction *f1 = [[Fraction allocF] initWith: 1 Over: 8 ];
	Fraction *f2 = [[Fraction allocF] initWith: 1 Over: 16 ];
	Fraction *resultF = [[Fraction allocF] init];
	int cnt;
	
	for(cnt = 1; cnt <= 3; ++cnt)
	{
		printf("\n");
		[f1 print];
		printf(" + ");
		[f2 print];
		printf(" = ");
		resultF = [f1 addValue: f2];
		[resultF print];
		
		f1 = resultF;
	
		printf("\n%i Fractions have been declared.\n", [Fraction getCount]);
		printf("\nThe Fraction addValue method has been called %i times.\n", [Fraction getAddCount]);
	}

	[f1 releaseF];
	[Fraction printCount];
	[f2 releaseF];
	[Fraction printCount];
	[resultF releaseF];
	[Fraction printCount];
	
    return 0;
}

In main.h, whenever I include "f1 = resultF" my code appears to run but then gives me an error that says Exec_Bad_Access.  If I comment that line out, the program terminates normally.  Why is this?

[skochan]

F1 and resultF reference the same Fraction object and so should not be released.  If that's a little unclear, please read this thread:

http://classroomm.com/objective-c/index.php?topic=56.0

Cheers,


Steve Kochan

[TheWatchfulOne]

Wow, Steve, thanks for such a quick reply!  I kind of see what you are saying.  This now brings up another question:  If f1 and resultF reference the same Fraction object, then does that mean I didn't have to allocate resultF?  Or maybe a better question would be, what happened to the memory that was used when resultF was allocated?  And how would it ever get released?

[skochan]

Please read through the thread reference I gave you, as it covers your question in detail.

Cheers,


Steve Kochan