Objective-C静态方法的结果保存到类实例变量，使用时给出“EXC_BAD_ACCESS”

Question

I am trying to store the md5 string as a class instance variable instead of the actual password. I have a static function that will return a md5 string which I'm trying to store in an instance variable instead of the actual password.

I have the following setter for my class instance variable:

-(void)setPassword:(NSString *)newpass{
 if(newpass != password){
  password = [utils md5HexDigest:newpass];
 }
}

This will pass back the correct md5 string and save it to the password variable in my init function: [self setPassword:pword];.

If I call another instance method and try to access self.password" I will get "EXC_BAD_ACCESS".

I understand that the memory is getting released, but I have no clue to make sure it stays.

I have tried alloc init with autorelease with no luck.

This is the md5HexDigest function getting called during the init (graciously found in another stackoverflow question):

+ (NSString*)md5HexDigest:(NSString*)input {
  const char* str = [input UTF8String];
  unsigned char result[CC_MD5_DIGEST_LENGTH];
  CC_MD5(str, strlen(str), result);

  NSMutableString *ret = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH*2];

  for(int i = 0; i<CC_MD5_DIGEST_LENGTH; i++)
    [ret appendFormat:@"%02x",result[i]];

  return ret;
}  

Any help/pointers would be greatly appreciated. I would rather have the md5 string saved in memory than the actual password calling the md5 every time I needed to use the password.

Thanks in advance.

Answer 1

Both David and pwc are correct, but missing an important detail.

setPassword: should copy the inbound parameter. This will both ensure that

• it is retain ed properly as the other answers imply and also that
• the set string is no longer mutable.

ie something like:

-(void)setPassword:(NSString *)newpass{
    [password release];
    password = [[utils md5HexDigest: newpass] copy];
}

Answer 2

Your setter needs to retain the new value (the one returned from [utils md5HexDigest:newpass] ). (and don't forget to release the old value too...)

Also, the test if(newpass != password) does not make any sense: newpass is an actual password, but password is the md5 digest.

Answer 3

The NSString returned by md5HexDigest is autoreleased (because NSMutableString stringWithCapacity returns an autoreleased string). You need to retain it in setPassword . Otherwise, it is being freed by the autorelease pool.