macOS segmentation fault

[jamesapp]

james-collinss-macbook-prorog17 jamescollins$ ./prog11.1a
1/3 + 2/5 = 11/15
1/3 - 2/5 = -1/15
1/3 * 2/5 = 2/15
1/3 / 2/5 = 5/6
Segmentation fault

got the above output when i ran a program from a book on Objective-C by Stephen G. Kochan, the program compiled without any error or warning messages.

here is my test program which i called prog11.1.m

#import "Fraction.h"
@interface Fraction (MathOps)
-(Fraction *) add: (Fraction *) f;
-(Fraction *) mul: (Fraction *) f;
-(Fraction *) sub: (Fraction *) f;
-(Fraction *) div: (Fraction *) f;
@end

@implementation Fraction (MathOps);
-(Fraction *) add: (Fraction *) f
{
  // To add two fractions:
  // a/b + c/d = ((a*d) + (b * c)) / (b * d)
  
  Fraction *result = [[Fraction alloc] init];
  int  resultNum, resultDenom;
  resultNum = (numerator * [f denominator]) +
    (denominator * [f numerator]);
  resultDenom = denominator * [f denominator];
  
  [result setTo: resultNum over: resultDenom];
  [result reduce];
  
  return [result autorelease];
}

-(Fraction *) sub: (Fraction *) f
{
  // To sub two fractions:
  // a/b - c/d = ((a*d) - (b*c)) / (b * d)
  
  Fraction *result = [[Fraction alloc] init];
  int  resultNum, resultDenom;
  
  resultNum = (numerator * [f denominator])-
    (denominator * [f numerator]);
    resultDenom = denominator * [f denominator];
    
    [result setTo: resultNum over: resultDenom];
    [result reduce];
    
    
    return [result autorelease];
}

-(Fraction *) mul: (Fraction *) f
{
  Fraction *result = [[Fraction alloc] init];
  
  [result setTo: numerator * [f numerator]
       over: denominator * [f denominator]];
  [result reduce];
  
  return [result autorelease];
}

-(Fraction *) div: (Fraction *) f
{
  Fraction *result = [[Fraction alloc] init];
  
  [result setTo: numerator * [f denominator]
            over: denominator * [f numerator]];
  [result reduce];
  
  return [result autorelease];
}
@end
int main (int argc, char *argv[])
{
  NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
  Fraction *a = [[Fraction alloc] init];
  Fraction *b = [[Fraction alloc] init];
  Fraction *result;
  
  [a setTo: 1 over: 3];
  [b setTo: 2 over: 5];
  
  [a print]; printf (" + "); [b print]; printf (" = ");
  result = [a add: b];
  [result print];
  printf ("\n");
  [result release];
  
  [a print]; printf (" - "); [b print]; printf (" = ");
  result = [a sub: b];
  [result print];
  printf ("\n");
  [result release];
  
  [a print]; printf (" * "); [b print]; printf (" = ");
  result = [a mul: b];
  [result print];
  printf ("\n");
  [result release];
  
  [a print]; printf (" / "); [b print]; printf (" = ");
  result = [a div: b];
  [result print];
  printf ("\n");
  [result release];
  [a release];
  [b release];
  
  
  [pool release];
  return 0;
}

one thing that i would like to mention is that the program compiled and ran ok with
the following line emitted

[pool release];

but when i added the above line i got a segmentation fault when i went to run the program, in the Kochan book a lot of the programs that i looked at in the later chapters like chapter 17 had pool release added?
do i need this line?
any help would be appreciated.

 

[Nutter]

You're over-releasing your result objects.

result = [a sub: b];
[result print];
printf ("\n");
[result release];

The method -sub: returns an autoreleased object, as all methods without "init" or "copy" in the name should. You shouldn't be releasing the result manually here, as it will be released later when you release the autorelease pool.

 

[yeroen]

Or even releasing anything at all, since this is a short running 1-pass program and all dynamically allocated memory will be reclaimed once the process exits.

Of course, the objection could be sustained that it's bad form not to explicitly deallocate memory.

 

[jamesapp]

thank you i dindn't know that.