为什么我的代码泄露了？

Question

UPDATE2 I think I found the true source of the leaks. I had some business objects that have string properties I forgot to release. These string properties were copied from my custom xlm node object, created here (KGYXMLNode) I don't understandt why the leak is reported here instead of my custom class. My NSString properties were copy and not retain .

UPDATE: I think it was a bug in Instruments or something or it doesn't magically leak anymore, but since xcode 4 it doesn't show this leak.

Hello, according to instruments i have a leak in the following code. I've built an objective-c wrapper around certain libxml functions to be able to parse xml docs using xpath, and in this method I'm setting the innerText for my custom node object.

-(void) SetInnerTextForNode: (xmlNodePtr) node : (KGYXMLNode *) obcNode
{
  if ((node) && (node->children))
  {
    for (xmlNodePtr pnode = node->children; pnode != NULL; pnode = pnode->next)
    {
      if (pnode->type == XML_TEXT_NODE)
      {
        xmlChar *content = pnode->content;
        NSString *innerText = [[NSString alloc] initWithUTF8String: (char *)content];
        NSString *trimmedText = [innerText stringByTrimmingCharactersInSet: trimCharSet];
        if (trimmedText.length > 0)
          obcNode.innerText = trimmedText;
        [innerText release];
        break;
      }
    }
  }
}

The leak is NSString *innerText = [[NSString alloc] initWithUTF8String: (char *)content]; . I don't know what is wrong.

Answer 1

You shouldn't access a node's content directly, instead use xmlNodeGetContent :

        xmlChar *content = xmlNodeGetContent(pnode);
        NSString *innerText = [[NSString alloc] initWithUTF8String: (char *)content];
        NSString *trimmedText = [innerText stringByTrimmingCharactersInSet: trimCharSet];
        if (trimmedText.length > 0)
          obcNode.innerText = trimmedText;
        [innerText release];
        // you must free what xmlNodeGetContent returns!
        xmlFree(content);
        break;

Answer 2

我不知道为什么你的代码泄漏了，但在我看来，你有一个不安全的自动释放对象分配给obcNode.innerText而不保留它。

Answer 3

This is a bit of a guess, but I think your dealloc method for obcnode does not release its innerText instance variable on deallocation. At first glance, your code fragment looks fine for memory management and that is the only potential error I can see.

The reason why it would be flagging the leak for innerText is possibly that trimmedText uses the same underlying unichar array as innerText but with different start and length values and therefore it retains innerText to stop the unichar array from going away.

Because trimmedText is an immutable string, sending copy to it merely causes it to send retain to itself and return itself, so obcNode owns trimmedText which owns innerText.