Guide To UNIX Using Linux Third Edition

Guide To UNIX Using LinuxThird Edition Chapter 10: Developing UNIX/Linux Applications in C and C++

Objectives • Understand basic elements of C programming • Debug C programs • Create, compile, and test C programs • Use the makeutility to revise and maintain source files Guide to UNIX Using Linux, Third Edition

Objectives (continued) • Identify differences between C and C++ programming • Create a simple C++ program • Create a C++ program that reads a text file • Create a C++ program that demonstrates how C++ enhances C functions Guide to UNIX Using Linux, Third Edition

Introducing C Programming • C is the language in which UNIX was developed and refined • C uses relatively short, isolated functions to break down large complex tasks into small and easily resolved subtasks • C’s function-oriented design allows programmers to create their own functions to interact with the predefined system functions Guide to UNIX Using Linux, Third Edition

Creating a C Program • A C program consists of separate bodies of code known as functions • The functions call each other as needed and work to solve the problem for which the program was originally designed Guide to UNIX Using Linux, Third Edition

Creating a C Program (continued) Guide to UNIX Using Linux, Third Edition

The C Library • The core C language is very small • C library consists of functions for many common activities including: • File, screen, and keyboard operations • String operations • Memory allocation and control • Math operations Guide to UNIX Using Linux, Third Edition

Program Format • A program includes 1 or more functions • Each program must have a main() function • Format for main is: int main() { } Guide to UNIX Using Linux, Third Edition

Including Comments • Comments begin with /* and end with */ • Compiler ignores everything in the comment • Comments can be anywhere in the file Guide to UNIX Using Linux, Third Edition

Using the Preprocessor #include Directive Using the preprocessor #include directive allowed for the output shown here Guide to UNIX Using Linux, Third Edition

Specifying Data Types Guide to UNIX Using Linux, Third Edition

Specifying Data Types (continued) Guide to UNIX Using Linux, Third Edition

Characters and Strings • Characters are represented internally in a single byte of computer memory • Character constants must be enclosed in single quotes • Strings are represented as arrays of characters • String constants must be enclosed in double quotes Guide to UNIX Using Linux, Third Edition

Variables • Variables must be declared before use • Declarations begin with a data type followed by one or more variable names • The scope of a variable is the part of the program in which the variable is accessible • Global variables can be accessed anywhere within a program Guide to UNIX Using Linux, Third Edition

Using Math Operators Guide to UNIX Using Linux, Third Edition

Generating Formatted Outputwith printf() The output of a simple C program Guide to UNIX Using Linux, Third Edition

Generating Formatted Outputwith printf() (continued) Guide to UNIX Using Linux, Third Edition

Using the C Compiler • Command for C compiler in Linux is gcc • In some UNIX systems, it is cc • Default executable file produced is a.out • Specify another name using the –o option • Information on options and use available at man gcc Guide to UNIX Using Linux, Third Edition

if Statements and C Loops • Use if statements to allow the program to make decisions depending on whether a condition is true or false • Three looping mechanisms: • for loop • while loop • do-while loop Guide to UNIX Using Linux, Third Edition

Using C Loops A C for loop generated the output in this program Guide to UNIX Using Linux, Third Edition

Defining Functions • When a function is defined, its name is declared and its statements are written • The data type of the return value must be declared in the function definition • Or “void” if no return value • Function prototypes must be included in programs to tell the compiler about functions that will be defined later Guide to UNIX Using Linux, Third Edition

Using Function Arguments • A value passed to a function is an argument • Arguments are stored in special automatic variables • Can be referred to from anywhere in the function Guide to UNIX Using Linux, Third Edition

Using Function Return Values • Functions can return values • Returned values can be used in assignment statements such as y=triple(x) • Must declare the type of the return value in the function definition Guide to UNIX Using Linux, Third Edition

Working with Files in C • Files are continuous streams of data • Typically stored on disk • File pointers point to predefined structures that contain information about the file • Before using a file, it must be opened • The library function for this is fopen • When done with a file, it must be closed • The library function for this is fclose Guide to UNIX Using Linux, Third Edition

Working with Files in C (continued) • File I/O uses various library functions • fgetc performs character input • fputc performs character output • During an input operation, it is essential to test for the end of a file • feof tests for the end-of-file marker Guide to UNIX Using Linux, Third Edition

Using the make Utility toMaintain Program Source Files • Some programs have many files of source code • Once compiled, the separate object files are linked into executable code • As program is updated, only need to recompile files that have changed Guide to UNIX Using Linux, Third Edition

Using the make Utility toMaintain Program Source Files (continued) • make utility helps tracks what needs to be recompiled by using the time stamp field for each source file • A control file, called the makefile, lists the source files and their relationship to each other Guide to UNIX Using Linux, Third Edition

Using the make Utility toMaintain Program Source Files (continued) • The make utility follows a set of rules • General rule definition includes • A target file • One or more dependencies • An action that creates the target Guide to UNIX Using Linux, Third Edition

Debugging Your Program • The compiler identifies some types of errors in a program • Common errors include: incorrect syntax, missing semicolons, case-sensitive errors • Steps to correct syntax errors: • Write down the error • Edit the source file • Save and recompile the file Guide to UNIX Using Linux, Third Edition

Creating a C Program to Accept Input • Use the scanf function to accept input from the keyboard • scanf uses a control string with format specified in a manner similar to printf • scanf can accept multiple inputs, but remember that this can lead to difficult and cumbersome code Guide to UNIX Using Linux, Third Edition

Creating a C Program to Accept Input (continued) Guide to UNIX Using Linux, Third Edition

Creating a C Program to Accept Input (continued) An example of using C to accept keyboard input Guide to UNIX Using Linux, Third Edition

Introducing C++ Programming • C++ adds object-oriented capabilities to C • C and C++ are similar in many ways • C++ uses functions, as does C, but includes the use of functions as methods for objects Guide to UNIX Using Linux, Third Edition

Introducing C++ Programming (continued) • The major differences between C and C++ • C follows procedural principles, whereas C++ follows object-oriented principles • C++ introduces “objects” • A collection of data and a set of operations called methods to manipulate the data Guide to UNIX Using Linux, Third Edition

Creating a Simple C++ Program Using C++ instead of C to create a program Guide to UNIX Using Linux, Third Edition

How C++ Enhances C Functions Function overloading allows C++ to use the same function name for different types of arguments Guide to UNIX Using Linux, Third Edition

Chapter Summary • C programs often consist of separate files called program modules that are compiled separately into object code and linked together to make up the program • The core C language is small, relying on libraries for extended functionality • UNIX was developed and refined in C Guide to UNIX Using Linux, Third Edition

Chapter Summary (continued) • A compiler translates source code into object code • A linker links all object code files plus library functions into an executable file • The make utility maintains source files • Only changed files need to be recompiled Guide to UNIX Using Linux, Third Edition

Chapter Summary (continued) • C is procedural and C++ is object-oriented • Function overloading: C++ offers a way to define a function to handle multiple sets of arguments Guide to UNIX Using Linux, Third Edition

Guide To UNIX Using Linux Third Edition