Borkware Quickies is a highly recommended collection of small, useful code snippets. Mark Dalrymple has been so kind to post one of my own there: “Making naked memory autoreleased”. Here’s a shorter and even more useful, though sometimes slower, version:

static void* tempCopyOf(void* data,UInt32 size) {
   void* buffer = calloc(1,size);
   if (buffer) {
      if (data) bcopy(data,buffer,size);
      [NSData dataWithBytesNoCopy:buffer length:size freeWhenDone:YES];
   return buffer;

So, you can call this as:

void* thing = tempCopyOf(&myStructure,sizeof(myStructure));

which will give you a temporary copy of myStructure, or as

void* thing = tempCopyOf(NULL,someSize);

which will return a zero-filled buffer of someSize for you to fill in as you want.