20.1. Introduction

We now discuss structures, their near equivalence with classes, and the manipulation of bits, characters and C strings. Many of the techniques we present here are included for the benefit of those who will work with legacy C and C++ code.

Like classes, C++ structures may contain access specifiers, member functions, constructors and destructors. In fact, the only differences between structures and classes in C++ is that structure members default to public access and class members default to private access when no access specifiers are used, and that structures default to public inheritance, whereas classes default to private inheritance. Our presentation of structures here is typical of the legacy C code and early C++ code you’ll see in industry.

We present a high-performance card shuffling and dealing simulation in which we use structure objects containing C++ string objects to represent the cards. We discuss the bitwise operators that allow you to access and manipulate the individual bits in bytes of data. We also present bitfields—special structures that can be used to specify the exact number of bits a variable occupies in memory. These bit-manipulation techniques are common in programs that interact directly with hardware devices that have limited memory. The chapter finishes with examples of many character and C string-manipulation functions—some of which are designed to process blocks of memory as arrays of bytes. The detailed C string treatment in this chapter is mostly for reasons of legacy code support and because there are still remnants of C string use in C++, such as command-line arguments (Appendix F). New development should use C++ string objects rather than C strings.