ChaPTEr 13: DEMYSTIFYING C++ I/O 409 Using Streams 410 What Is a Stream, Anyway? 410 Stream Sources and Destinations 411 Output with Streams 411 Output Basics 412 Methods of Output Streams 412 Handling Output Errors 414 Output Manipulators 415 Input with Streams 417 Input Basics 417 Handling Input Errors 418 Input Methods 419 Input Manipulators 423 Input and Output with Objects 423 String Streams 425 File Streams 426 Text Mode versus Binary Mode 427 Jumping around with seek() and tell() 428 Linking Streams Together 430 Bidirectional I/O 431 Summary 432
Please note that all the code examples for this chapter are available as a part of this chapter’s code download on the book’s website at www.wrox.com/go/proc++4e on the Download Code tab. A program’s fundamental job is to accept input and produce output. A program that produces no output of any sort would not be very useful. All languages provide some mechanism for I/O, either as a built-in part of the language or through an OS-specific API. A good I/O sys- tem is both flexible and easy to use. Flexible I/O systems support input and output through a variety of devices, such as files and the user console. They also support reading and writing of different types of data. I/O is error-prone because data coming from a user can be incorrect or the underlying file system or other data source can be inaccessible. Thus, a good I/O system is also capable of handling error conditions. If you are familiar with the C language, you have undoubtedly used printf() and scanf() . As I/O mechanisms, printf() and scanf() are certainly flexible. Through escape codes and variable placeholders, they can be customized to read in specially formatted data, or output any value that the formatting codes permit, which is currently limited to integer/character val- ues, floating point values, and strings. However, printf() and scanf() falter on other mea- sures of good I/O systems. They do not handle errors particularly well, they are not flexible enough to handle custom data types, and in an object-oriented language like C++, they are not at all object oriented.1.USING STREAMS
The stream metaphor takes a bit of getting used to. At first, streams may seem more complex than traditional C-style I/O, such as printf() . In reality, they seem complicated initially only because there is a deeper metaphor behind streams than there is behind printf() . Don’t worry, though; after a few examples, you’ll never look back.
1.1 What Is a Stream, Anyway?Chapter 1 compares the cout stream to a laundry chute for data. You throw some variables down the stream, and they are written to the user’s screen, or console. More generally, all streams can be viewed as data chutes. Streams vary in their direction and their associated source or destination. For example, the cout stream that you are already familiar with is an output stream, so its direction is “out.” It writes data to the console so its associated destination is “console.” The c in cout does not stand for “console” as you might expect, but stands for “character” as it’s a character-based stream. There is another standard stream called cin that accepts input from the user. Its direction is “in,” and its associated source is “console.” As with cout , the c in cin stands for “character.” Both cout and cin are predefined instances of streams that are defined within the std namespace in C++. The following table gives a brief description of all predefined streams. The difference between buffered and unbuffered streams is that a buffered stream does not immediately send the data to the destination, but instead, it buffers incoming data and then sends it in blocks. An unbuffered stream, on the other hand, immediately sends the data to the destination.Buffering is usually done to improve performance, as certain destinations, such as files, perform better when writing bigger blocks at once. Note that you can always force a buffered stream to send all its currently buffered data to the destination by flushing its buffer using the flush() method.暑期编程PK赛 得CSDN机械键盘等精美礼品！
