E.2. Redirecting Input/Output on UNIX/LINUX/Mac OS X and Windows Systems

E 2 Redirecting Input Output on UNIX LINUX Mac OS X and Windows Systems

Normally, the input to a program is from the keyboard (standard input), and the output from a program is displayed on the screen (standard output). On most computer systemsUNIX, LINUX, Mac OS X and Windows systems in particularit is possible to redirect inputs to come from a file, and redirect outputs to be placed in a file. Both forms of redirection can be accomplished without using the file-processing capabilities of the standard library.

There are several ways to redirect input and output from the UNIX command line. Consider the executable file sum that inputs integers one at a time, keeps a running total of the values until the end-of-file indicator is set, then prints the result. Normally the user inputs integers from the keyboard and enters the end-of-file key combination to indicate that no further values will be input. With input redirection, the input can be stored in a file. For example, if the data are stored in file input, the command line

 $ sum < input

causes program sum to be executed; the redirect input symbol (<) indicates that the data in file input (instead of the keyboard) is to be used as input by the program. Redirecting input in a Windows Command Prompt is performed identically.

Note that $ represents the UNIX command-line prompt. (UNIX prompts vary from system to system and between shells on a single system.) Redirection is an operating-system function, not another C++ feature.

The second method of redirecting input is piping. A pipe (|) causes the output of one program to be redirected as the input to another program. Suppose program random outputs a series of random integers; the output of random can be "piped" directly to program sum using the UNIX command line

 $ random | sum

This causes the sum of the integers produced by random to be calculated. Piping can be performed in UNIX, LINUX, Mac OS X and Windows.

Program output can be redirected to a file by using the redirect output symbol (>). (The same symbol is used for UNIX, LINUX, Mac OS X and Windows.) For example, to redirect the output of program random to a new file called out, use

 $ random > out

Finally, program output can be appended to the end of an existing file by using the append output symbol (>>). (The same symbol is used for UNIX, LINUX, Mac OS X and Windows.) For example, to append the output from program random to file out created in the preceding command line, use the command line

 $ random >> out

Introduction to Computers, the Internet and World Wide Web

Introduction to C++ Programming

Introduction to Classes and Objects

Control Statements: Part 1

Control Statements: Part 2

Functions and an Introduction to Recursion

Arrays and Vectors

Pointers and Pointer-Based Strings

Classes: A Deeper Look, Part 1

Classes: A Deeper Look, Part 2

Operator Overloading; String and Array Objects

Object-Oriented Programming: Inheritance

Object-Oriented Programming: Polymorphism


Stream Input/Output

Exception Handling

File Processing

Class string and String Stream Processing

Web Programming

Searching and Sorting

Data Structures

Bits, Characters, C-Strings and structs

Standard Template Library (STL)

Other Topics

Appendix A. Operator Precedence and Associativity Chart

Appendix B. ASCII Character Set

Appendix C. Fundamental Types

Appendix D. Number Systems

Appendix E. C Legacy Code Topics

Appendix F. Preprocessor

Appendix G. ATM Case Study Code

Appendix H. UML 2: Additional Diagram Types

Appendix I. C++ Internet and Web Resources

Appendix J. Introduction to XHTML

Appendix K. XHTML Special Characters

Appendix L. Using the Visual Studio .NET Debugger

Appendix M. Using the GNU C++ Debugger


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C++ How to Program
C++ How to Program (5th Edition)
ISBN: 0131857576
EAN: 2147483647
Year: 2004
Pages: 627
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