LibrariesLibraries

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Making Functions Globally Reusable(§ 6.4)

ReviewReviewWe have written a program that used functions to compute the area and circumference of ellipses.

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double ellipseArea(double length, double width);

double ellipseCircumference(double length, double width);

Function Prototypes (placed before main()):

Function Definitions & Documentation(placed after main()):const double PI = 3.14159;

/* Function to compute the area of an ellipse Receive: two double values length, width, representing the major axis and minor axis of an ellipse Return: the area of the ellipse -------------------------------------------------------*/double ellipseArea(double length, double width){ double halfLength = length/2.0, halfWidth = width/2.0; return PI * halfLength * halfWidth; }

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Putting these prototypes, documentation, and definitions along with main() in the same program makes it possible to reuse them at several different places in the program. However, suppose that in order to solve some other problem, a different program requires computing the area and circumference of an ellipse.

double ellipseCircumference(double length, double width){ double halfLength = length/2.0, halfWidth = width/2.0;

return 2.0 * PI * sqrt( (halfLength * halfLength + halfWidth * halfWidth) /

2.0);}

/* Function to compute the circumference of an ellipse Receive: two double values length, width, representing the major axis and minor axis of an ellipse Return: the circumference of the ellipse ---------------------------------------------------------*/

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_____

_______We also

have global reusability.

How can we reuse our functions in a different program?

Options:• Copy-and-paste ellipseArea()

and ellipseCircumference()from our previous program into the new program.

• Store ellipseArea() and ellipseCircumference()in a ___________ so that programs can share them.

Is there automatic updating

of a program

if the original functions are

modified?

LibrariesLibrariesA library consists of three files:A _____________ file (whose name has a .h suffix) that contains shareable function __________________ and ____________.An ________________________ file (whose name has a .cpp suffix) that contains shareable function _____________________.A ____________________ file (whose name hasa .txt (or .doc) suffix) that contains documentation for the library.

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Header Files

In Visual C++, put all 3 and the program that uses the library in the same project.

Source Files

Resource Files

ExampleExample

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Other Examples:Text: Temperature conversionProject: Metric conversion

Since we are creating a library to share functions that describe an ellipse, we might name our library ellipse, with • header file ellipse.h,• implementation file ellipse.cpp, and• documentation file ellipse.txt.

must be the same

In ellipse.h, we place the function________________:

The corresponding implementation file ellipse.cpp and any program that uses these functions must contain

___________________________

/*----- ellipse.h ----- Library of functions for computing ellipse attributes.

L. Nyhoff CS 104X Jan 16, 2012

Functions provided: ellipseArea: compute area of an ellipse ellipseCircumference: compute circumference of an ellipse ------------------------------------------------------------*/

double ellipseArea(double length, double width);double ellipseCircumference(double length, double width);// ... plus any others we want to provide such as the// ... focal length, eccentricity, etc.

Note the "directory"

Header file: ellipse.h

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Can use this same opening documentation in all 3 files

but change1st line

Their _______________ are placed in ellipse.cpp:

_______________________

const double PI = 3.14159; // Could go in ellipse.h

double ellipseArea(double length, double width){ ________________________________________ double halfLength = length/2.0, halfWidth = width/2.0; return PI * halfLength * halfWidth;}

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Put afterusing namespace std;

/*----- ellipse.cpp ----- Library of functions for computing ellipse attributes.

L. Nyhoff CS 104X Jan 16, 2012

Functions provided: ellipseArea: compute area of an ellipse ellipseCircumference: compute circumference of an ellips ------------------------------------------------------------*/#include <cmath>#include <cassert>using namespace std;

Implementation file: ellipse.cpp

double ellipseCircumference(double length, double width){ assert(length >= 0 && width >= 0); double halfLength = length/2.0, halfWidth = width/2.0;

return 2.0 * PI * sqrt((halfLength * halfLength + halfWidth * halfWidth)/2.0);}

//... plus definitions of any others we provide ...

This file can be __________________ separately from any program that uses it (called a _______________ program). 10

Implementation file (cont.)

Our documentation file will be a copy of the header file, with __________________________ added foradditional documentation:

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/*----- ellipse.cpp ----- Library of functions for computing ellipse attributes.

L. Nyhoff CS 104X Jan 17, 2011

Functions provided: ellipseArea: compute area of an ellipse ellipseCircumference: compute circumference of an ellips ------------------------------------------------------------*/

/*------------------------------------------------------- Compute the area of an ellipse. Receive: length, width, two double values. Return: the area of the corresponding ellipse. -------------------------------------------------------*/double ellipseArea(double length, double width);

Documentation file: ellipse.txt

By storing the documentation in a separate file, we provide information on how to use the library without cluttering the other library files.

12But some programmers

do put the documentation

in the header file.

/*------------------------------------------------------- Compute the circumference of an ellipse. Receive: length, width, two double values. Return: the circumference of ellipse defined by length and width. -------------------------------------------------------*/double ellipseCircumference(double length, double width);

// ... plus prototypes and specifications // ... for any others we provide ...

Documentation file (cont.)

Program TranslationTranslating a program into machine

language consists of two steps:1. ________________, in which the syntax of

the main program and of the implementation files of any included libraries are checked, and if no errors are found, converts them into the computer’s machine language.

2. ___________, in which any calls to functions (from main() or from other functions) are bound to the definitions of those functions.

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Using a LibraryUsing a Library

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To use a library:A program must ________________________(usually above the main function and after using namespace std;). When the ___________ (actually its preprocessor) encounters this #include directive, it must be able to find the header file so it can open it and replace the #includedirective with its contents so they get compiled along with the program.When the file contains function prototypes, the effect of the #include directive is to insert those prototypes into the program.

Put it in the project's

header files

In Visual C++:

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It must also be able to find the corresponding implementation file so it can open it, insert the contents of its header file into it, and then compile it (separately from the program).

Put it in the project's

source files

In Visual C++:

Once these compilations are successful, the ___________ combines these compiled files into one, connecting(i.e., "linking") each function call to the compiledcode of that function's definition.

A failure in either stage is an error.

Compilation ErrorsCompilation ErrorsA program calling a function for which _________________is given produces a ________________ error.

This can occur if you call a library function and neglect to #include the header file containing its prototype.You’ll be trying to use a function that has not been ______________.

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Linking ErrorsLinking ErrorsA program calling a function for which thelinker cannot find a ____________________ produces a linker error.This can occur if a program calls a function but the linker is not told to use the library implementation file or object file containing that function’s definition.How this is done varies from platform to platform, but often involves a project file.

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Example#include <iostream> // cin, cout, <<, >>, ...using namespace std;

#include "ellipse.h" // insert ellipse prototypes

int main(){ cout << "Program to compute the area and circumference of ellipses.\n";

double majorAxis, minorAxis; cout << "\nEnter major & minor axes (in meters) (0 0 to stop): "; cin >> majorAxis >> minorAxis; while (majorAxis > 0) { double area = ellipseArea(majorAxis, minorAxis);

double circumference = ellipseCircumference(majorAxis, minorAxis);

cout << "\nFor an ellipse with major axis " << majorAxis << " meters and minor axis " << minorAxis << " meters\n" << "\tarea = " << area << " sq. meters\n" << "\tcircumference = " << circumference << " meters\n"; cout << "\nEnter major & minor axes (in meters) (0 0 to stop): "; cin >> majorAxis >> minorAxis; }} 18

Put afterusing namespace std;

Temperature

conversion example in

the text

1>------ Rebuild All started: Project: EllipseLib, Configuration: Debug Win32 ------1> ellipse.cpp1> driver.cpp1> Generating Code...1> EllipseLib.vcxproj -> E:\CS104-12Int\classprogs\EllipseLib\Debug\EllipseLib.exe========== Rebuild All: 1 succeeded, 0 failed, 0 skipped ==========

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EXECUTION:

Program to compute the area and circumference of ellipses.

Enter major & minor axes (in meters) (0 0 to stop): 2 2

For an ellipse with major axis 2 meters and minor axis 2 meters area = 3.14159 sq. meters circumference = 6.28318 meters

Enter major & minor axes (in meters) (0 0 to stop): 0 0Press any key to continue . . .

Compilation creates a ____________________file(usually with a .o or .obj suffix) from a .cpp file.

int main(){ // ...}

C++Compiler

0010011101010110001001...11101100100

file.cpp file.obj

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LinkingLinking

0010011101010110001001...11101100100

C++Linker

0010011101010110001001...11101100100 1110010101110010001000...101011011010110110101111010101001...00101100100

file1.obj

file.exe

1110010101110010001000...10101101101

file2.obj

0110110101111010101001...00101100100

fileN.obj

Linking binds multiple ______________filesinto a single ______________________ file that can be executed by the operating system.

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OCD with LibrariesOCD with Libraries1. Specify the desired behavior of the program.2. Identify the objects needed.3. Identify the operations.

a. If an operation is not predefined:Write a function to perform it.

b. If an operation is likely to be reusable someday:Store its function in a library and access it

from there.4. Organize objects and operations into an algorithm.

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ExtendingC++