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C + + : T h e C o m p l e t e R e f e r e n c e
C
++ supports two complete I/O systems. The first it inherits from C. The second is the object-oriented I/O system defined by C++. This and the next chapter discuss the C-like I/O system. (Part Two examines C++ I/O.) While you will probably want to use the C++ I/O system for most new projects, C-style I/O is still quite common, and knowledge of its features is fundamental to a complete understanding of C++.
In C, input and output are accomplished through library functions. There are both console and file I/O functions. Technically, there is little distinction between console
I/O and file I/O, but conceptually they are in very different worlds. This chapter examines in detail the console I/O functions. The next chapter presents the file I/O system and describes how the two systems relate.
With one exception, this chapter covers only console I/O functions defined by
Standard C++. Standard C++ does not define any functions that perform various screen control operations (such as cursor positioning) or that display graphics, because these operations vary widely between machines. Nor does it define any functions that write to a window or dialog box under Windows. Instead, the console
I/O functions perform only TTY-based output. However, most compilers include in their libraries screen control and graphics functions that apply to the specific environment in which the compiler is designed to run. And, of course, you may use C++ to write
Windows programs, but keep in mind that the C++ language does not directly define functions that perform these tasks.
The Standard C I/O functions all use the header file stdio.h. C++ programs can also use the C++-style header <cstdio>.
This chapter refers to the console I/O functions as performing input from the keyboard and output to the screen. However, these functions actually have the standard input and standard output of the system as the target and/or source of their I/O operations. Furthermore, standard input and standard output may be redirected to other devices. These concepts are covered in Chapter 9.
An Important Application Note
Part One of this book uses the C-like I/O system because it is the only style of I/O that is defined for the C subset of C++. As explained, C++ also defines its own object-oriented I/O system. For most C++ applications, you will want to use the
C++-specific I/O system, not the C I/O system described in this chapter. However, an understanding of C-based I/O is important for the following reasons:
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At some point in your career you may be called upon to write code that is restricted to the C subset. In this case, you will need to use the C-like I/O functions.
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For the foreseeable future, C and C++ will coexist. Also, many programs will be hybrids of both C and C++ code. Further, it will be common for C programs to be "upgraded" into C++ programs. Thus, knowledge of both the C and the C++
