The most important thing to keep in mind for Memcheck's reporting of memory leaks is that a lot of reported leaks may in fact not be leaks. This is reflected in the way Memcheck reports any potential issues it finds, which is as follows:

• Definitely lost
• Indirectly lost
• Possibly lost

Of the three possible report types, the Definitely lost type is the only one where it is absolutely certain that the memory block in question is no longer reachable, with no pointer or reference remaining, which makes it impossible for the application to ever free the memory.

In case of the Indirectly lost type, we did not lose the pointer to these memory blocks themselves, but, the pointer to a structure which refers to these blocks instead. This could, for example, occur when we directly lose access to the root node of a data structure (such as a red/black or binary tree). As a result, we also lose the ability to access any of the child nodes.

Finally, Possibly lost is the catch-all type where Memcheck isn't entirely certain whether there is still a reference to the memory block. This can happen where interior pointers exist, such as in the case of particular types of array allocations. It can also occur through the use of multiple inheritance, where a C++ object uses self-reference.

As mentioned earlier in the basic use section for Memcheck, it's advisable to always run Memcheck with --leak-check=full specified to get detailed information on exactly where a memory leak was found.