Chapter 1

{
__UHEAP_MARK;
__UHEAP_SETFAIL(RHeap::EFailNext, i);
TRAPD(error, TestFunctionL());
__UHEAP_MARKEND;
TAny* testAlloc = User::Alloc(1);
TBool heapTestingComplete = (testAlloc == NULL);
User::Free(testAlloc);
if ((error != KErrNoMemory) && heapTestingComplete)
break;
}
This loop runs the test function in such a way that each time through, one more successful
heap allocation is allowed. It is guaranteed that there will be a KErrNoMemory error (if
nothing else) that will cause a leave and cleanup. Any failure to clean up properly will be
caught by the heap-balance checks. The loop terminates when the test function has
completed without generating a memory-allocation failure.
6.9 Summary
Memory and other resources are scarce in typical Symbian OS environments. Your
programs will encounter resource shortages, and must be able to deal with them. You must
avoid memory leaks, both under normal circumstances and when dealing with errors.
Symbian OS provides an industrial-strength framework to support you, with very low
programmer overhead, and very compact code.
In this chapter, we've seen the following:
� How the debug keys, and their simulated failures, and the heap- checking tools built
into CONE, mean that testing your code is easy.
� How naming conventions help with error handling and cleanup.
� Allocating and destroying objects on the heap – how to preserve heap balance, what to
do if allocation fails, how to reallocate safely.
� How leaves work, the TRAP() and TRAPD() macros, and Symbian OS error codes.
� When to use your own traps.
� When and how to use the cleanup stack.
� Two-phase construction, using ConstructL() and the NewL() and NewLC() factory
functions.
� What CBase provides for any C class to help with cleanup.
� Cleanup for R and T classes.
� How to panic a program, and test engines and libraries.
I've covered a lot of material in this chapter, and you could be forgiven for not taking it all in
at once. Don't worry – if you only remember one thing from this chapter, remember that
cleanup is vital. You'll see cleanup-related disciplines in all the code throughout the rest of
the book, and you'll be able to come back here for reference when you need to.