Why does this program take up so much memory?

Question

I am learning Objective-C. I am trying to free all the memory that I use. So, I wrote a program to check if I am doing this correctly:

#import <Foundation/Foundation.h>

#define DEFAULT_NAME @"Unknown"

@interface Person : NSObject
{
  NSString *name;
}
@property (copy) NSString * name;
@end

@implementation Person
@synthesize name;
- (void) dealloc {
  [name release];
  [super dealloc];
}
- (id) init {
  if (self = [super init]) {
    name = DEFAULT_NAME;
  }
  return self;
}
@end


int main (int argc, const char * argv[]) {
  NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
  Person *person = [[Person alloc] init];
  NSString *str;
  int i;

  for (i = 0; i < 1e9; i++) {
    str = [NSString stringWithCString: "Name" encoding: NSUTF8StringEncoding];
    person.name = str;
    [str release];
  }

  [person release];
  [pool drain];
  return 0;
}

I use a mac with a snow leopard. To check how much memory is being used, I open Activity Monitor at the same time as it starts. After a couple of seconds, it uses gigabytes of memory. What can I do to prevent it from being used so much?

Answer 1

Firstly, your loop is incorrect. +stringWithCString:…is not +alloc/ +new…/ -copyso you do not have -releaseit.

Is one of them true:

2. Not -release:

   str = [NSString stringWithCString: "Name" encoding: NSUTF8StringEncoding];
   person.name = str;
   

3. Use -init:

   str = [[NSString alloc] initWithCString: "Name" encoding: NSUTF8StringEncoding];
   person.name = str;
   [str release];
   

, -[Person init]:

- (id) init {
  if ((self = [super init])) {
    name = [DEFAULT_NAME copy]; // <----
  }
  return self;
}

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,

str = [NSString stringWithCString: "Name" encoding: NSUTF8StringEncoding];

str = [[[NSString alloc] initWithCString:......] autorelease];

an -autorelease d " NSAutoreleasePool ".

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