Libraries
Making Functions Globally Reusable
(§ 4.6)
1
Review
We have written a program that used functions to
compute the area and circumference of an ellipse.
area  ab
a
b
b
a
a b
circumference  2
2
2
2
2
Function Prototypes (placed before main()):
double ellipseArea(double length, double width);
double ellipseCircumference(double length, double width);
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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/* 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
---------------------------------------------------------*/
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);
}
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.
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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?
_____
_______
We also
have global
reusability.
5
Libraries
A library consists of three files:
A _____________ file (whose name has a
.h suffix) that contains shareable
Header
Files
function __________________________________.
An ________________________ file (whose name
has a .cpp suffix) that contains shareable
function _____________________.
A ____________________ file (whose name has
a .txt (or .doc) suffix) that contains
documentation for the library.
Source
Files
Resource
Files
In Visual C++, put all 3 and
the program that uses the
library in the same project.
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Example
Since we are creating a library to
share functions that describe an ellipse,
we might name our library ellipse,
with
must be
• header file ellipse.h,
the same
• implementation file ellipse.cpp, and
• documentation file ellipse.txt.
Other Examples:
Text: Temperature conversion
Project: Metric conversion
7
Function Prototypes (placed before main()):
double ellipseArea(double length, double width);
double ellipseCircumference(double length, double width);
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;
}
•adams@calvin.edu
return PI * halfLength
* halfWidth;
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Implementation file: ellipse.cpp
Their _______________ are placed in ellipse.cpp:
/*----- ellipse.cpp ----Library of functions for computing ellipse attributes.
L. Nyhoff
CS 104X
Oct 12, 2009
Functions provided:
ellipseArea: compute area of an ellipse
ellipseCircumference: compute circumference of an ellips
------------------------------------------------------------*/
#include <cmath>
#include <cassert>
Put after
using namespace std;
using namespace std;
_______________________
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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Implementation file (cont.)
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((pow(halfLength, 2.0) + pow(halfWidth, 2.0))/2.0);
}
//... plus definitions of any others we provide ...
This file can be ___________________________ from any
program that uses it (called a ______________________).
1
0
Documentation file: ellipse.txt
Our documentation file will be a copy of the
header file, with __________________________
added foradditional documentation:
/*----- ellipse.cpp ----Library of functions for computing ellipse attributes.
L. Nyhoff
CS 104X
Oct 12, 2009
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);
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Documentation file (cont.)
/*------------------------------------------------------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 ...
By storing the documentation in a separate file,
we provide information on how to use the library
without cluttering the other library files.
But some programmers
do put the documentation
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in the header file.
Program Translation
Translating 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.
13
Using a Library
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 #include
directive with its contents so they get compiled
along with the program.
In Visual C++:
Put it in the
project's header
files
When the file contains function prototypes, the effect of
the #include directive is to insert those prototypes
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into the program.
In Visual C++:
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
Once these compilations are successful, the ___________
combines these compiled files into one, connecting
(i.e., "linking") each function call to the compiled
code of that function's definition.
A failure in either stage is an error.
15
Compilation Errors
A program _________________________________
______________is given produces a compiler 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 Errors
A program calling a function for which the
____________________________________
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.
17
Temperature
conversion
example in
the text
Example
#include <iostream>
using namespace std;
// cin, cout, <<, >>, ...
_______________________________
// insert ellipse prototypes
Put after
int main()
using namespace std;
{
cout << "Program to compute the area and circumference of "
"an ellipse.\n";
cout << "Please enter its major & minor axes (meters): ";
double majorAxis, minorAxis;
cin >> majorAxis >> minorAxis;
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";
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------ Build started: Project: Ellipse, Configuration: Debug Win32 ------
Compiling...
ellipse.cpp
driver.cpp
Generating Code...
Linking...
Build log was saved at "file://e:\CS104\Ellipse\Ellipse\Debug\BuildLog.htm"
Ellipse - 0 error(s), 0 warning(s)
---------------------- Done ---------------------Build: 1 succeeded, 0 failed, 0 skipped
EXECUTION:
Program to compute the area and circumference of an ellipse.
Please enter its major & minor axes (meters): 2 2
For an ellipse with major axis 2 meters and minor axis 2 meters
area = 3.14159 sq. meters
circumference = 6.28318 meters
Press any key to continue
19
Compilation creates a ____________________file
(usually with a .o or .obj suffix) from a
.cpp file.
int main()
{
// ...
}
file.cpp
C++
Compiler
00100111010
10110001001
...
11101100100
file.obj
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Linking
Linking binds multiple ____________________
into a single ____________________________
that can be run.
file1.obj
file2.obj
fileN.obj
00100111010
10110001001
...
11101100100
11100101011
10010001000
...
10101101101
01101101011
11010101001
...
00101100100
C++
Linker
00100111010
10110001001
...
11101100100
11100101011
10010001000
...
10101101101
01101101011
11010101001
...
00101100100
file.exe
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OCD with Libraries
1. Specify the desired behavior of the program.
2. Identify the objects needed.
3. Identify the operations.
a. If an operation is not predefined:
•Extending
C++
Write a function to perform it.
b. If an operation is likely to be reusable someday:
Store its function in a library and asccess it from there.
4. Organize objects and operations into an algorithm.
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