10 - Memory Leaks and Their Debugging

Summary

Classification of the causes of memory leaks. Tracing memory leaks in C programs using location reporting and allocation/deallocation information-gathering versions of the C allocators and deallocators. Tracing memory leaks in C++ programs: overloading the operators new and delete and the problems it causes. Techniques for location tracing. Counting objects in C++. Smart pointers as a remedy for memory leaks caused by the undetermined ownership problem.

As mentioned previously, I do not like the terms “memory leaks” or “leaking memory”. They somehow put the onus on memory, as if it were the memory's inadequacy that caused the problem. Every time I hear a project manager or a student explain in a grave tone of voice that “the project is delayed because we have memory leaking”, I feel like retorting “OK, find a better memory that doesn't leak”. In truth, it's not the memory but rather the program that is inadequate. We should be talking about leaking programs, not about leaking memory. In this chapter we will classify the most common problems leading to memory leaks and discuss how to identify and locate them. We will start with trivial and obvious problems and proceed to more subtle ones that are harder to deal with.

The first class of memory leaks is called orphaned allocation and is characterized by allocation of a memory segment whose address is not preserved for later deallocation.