Memory Access

Arrays and pointers are low-level building blocks of C programs that provide fast access to hardware memory. This chapter discusses the different ways to organize and access memory.

22.1	Pointer Pathology	504
22.2	Further Pointer Pathology with Heap Memory	506
22.3	Memory Access Summary	509
22.4	Introduction to Arrays	509
22.5	Pointer Arithmetic	510
22.6	Arrays, Functions, and Return Values	511
22.7	Different Kinds of Arrays	513
22.8	Valid Pointer Operations	513
22.9	What Happens If new Fails?	515
22.10	Chapter Summary	519

Direct manipulation of memory entails some serious risks and requires good practices and thorough testing to avoid serious errors. Improper use of pointers and dynamic memory can cause program crashes that result from heap corruption and memory leaks. Heap corruption is especially difficult to debug because it generally leads to segmentation faults that halt the program at a point in the code that may be far from the point at which the heap became corrupted.

Both Qt and Standard Library container classes permit the safe use of dynamic memory without adversely affecting performance.[1] Arrays are used to implement most container classes but are hidden from client code. The safety factors come from the careful design of each container API so that actions that might produce memory problems are not permitted.

[1] In the sequel, whenever we use the term container, with no further qualification, we mean Qt or Standard Library container.

Qt offers many containers, ranging from high-level template classes such as the ones we discussed in Section 10.2 to low-level containers such as QBitArray and QByteArray.

Generally, when writing applications that reuse those containers, it is easy to avoid the use of arrays entirely. When Qt is not available, or when you are writing an interface to C code, you may need to use arrays and pointers and work directly with allocated memory.