Developing UNIX/Linux Applications in C and C

1
Guide To UNIX Using Linux Third Edition

• Chapter 10
• Developing UNIX/Linux Applications in C and C

2
Objectives

• Understand basic elements of C programming
• Debug C programs
• Create, compile, and test C programs
• Use the make utility to revise and maintain
  source files

3
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

4
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
• Cs function-oriented design allows programmers
  to create their own functions to interact with
  the predefined system functions

5
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

6
Creating a C Program (continued)
7
Creating a C Program (continued)
8
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

9
Program Format

• A program includes 1 or more functions
• Each program must have a main() function
• Format for main is
• int main()

10
Including Comments

• Comments begin with / and end with /
• Compiler ignores everything in the comment
• Comments can be anywhere in the file

11
Using the Preprocessor include Directive
Using the preprocessor include directive allowed
for the output shown here
12
Specifying Data Types
13
Specifying Data Types (continued)
14
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

15
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

16
Using Math Operators
17
Generating Formatted Outputwith printf()
The output of a simple C program
18
Generating Formatted Outputwith printf()
(continued)
19
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

20
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

21
Using C Loops
A C for loop generated the output in this program
22
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

23
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

24
Using Function Return Values

• Functions can return values
• Returned values can be used in assignment
  statements such as ytriple(x)
• Must declare the type of the return value in the
  function definition

25
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

26
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

27
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

28
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

29
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

30
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

31
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

32
Creating a C Program to Accept Input (continued)
33
Creating a C Program to Accept Input (continued)
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Creating a C Program to Accept Input (continued)
An example of using C to accept keyboard input
35
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

36
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

37
Creating a Simple C Program
Using C instead of C to create a program
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How C Enhances C Functions
Function overloading allows C to use the same
function name for different types of arguments
39
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

40
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

41
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