当函数返回malloc()的结果时，如何在malloc()之后释放()?

问题描述

我有以下实例方法(改编自《 iPhone应用程序编程指南》中事件处理"部分的清单3-6 ):

I have the following instance method (adapted from Listing 3-6 of the Event Handling section in the iPhone Application Programming Guide):

- (CGPoint)originOfTouch:(UITouch *)touch
{
    CGPoint *touchOriginPoint = (CGPoint *)CFDictionaryGetValue(touchOriginPoints, touch);
    if (touchOriginPoint == NULL)
    {
        touchOriginPoint = (CGPoint *)malloc(sizeof(CGPoint)); // leaks
        CFDictionarySetValue(touchOriginPoints, touch, touchOriginPoint);
        *touchOriginPoint = [touch locationInView:touch.view];
    }
    return *touchOriginPoint;
}

由于对 malloc()的调用，我的应用程序有时每隔16个字节就会泄漏一次.我不确定如何在 free()也返回它的同时返回 touchOriginPoint .

Every once in a while my app leaks 16 Bytes as a result of the call to malloc(). I'm not sure how to return touchOriginPoint while free()ing it as well.

推荐答案

如果您不关心次要的性能损失，请使用 NSMutableDictionary 并将该点存储为 NSValue :

If you do not care a minor performance loss, use an NSMutableDictionary and store the point as an NSValue:

NSValue* touchOriginPointValue = [touchOriginPoints objectForKey:touch];
if (touchOriginPointValue == nil) {
   touchOriginPointValue = [NSValue valueWithCGPoint:[touch locationInView:touch.view]];
   [touchOriginPoints setObject:touchOriginPointValue forKey:touch];
}
return [touchOriginPointValue CGPointValue];

---

如果必须使用 CFDictionary 方法，则必须找到一个地方，以在没有值的情况下 free 那些 malloc -ed的内存需要.因此，创建字典时必须传递值回调

---

If you must use the CFDictionary approach, you have to find a place to free those malloc-ed memory when the values are not needed. Therefore, you have to pass the values callbacks when creating the dictionary

static void free_malloced_memory (CFAllocatorRef allocator, const void *value) {
   free((void*)value);
}
static const CFDictionaryValueCallBacks values_callbacks = {0, NULL, free_malloced_memory, NULL, NULL};
...
touchOriginPoints = CFDictionaryCreateMutable(NULL, 0, &kCFTypeDictionaryKeyCallBacks, & values_callbacks);
...

这篇关于当函数返回malloc()的结果时，如何在malloc()之后释放()?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！