ADTs
Steven J Zeil
1 Abstraction
In general, abstraction is a creative process of focusing attention on the main problems by ignoring lower-level details.
In programming, we encounter two particular kinds of abstraction:
- procedural abstraction and
- data abstraction.
1.1 Procedural Abstraction
A procedural abstraction is a mental model of what we want a subprogram to do (but not how to do it).
Example: if you wanted to compute the length of the a hypotenuse of a right triangle, you might write something like
double hypotenuse = sqrt(side1*side1 + side2*side2);
We can write this, understanding that the sqrt function is supposed to compute a square root, even if we have no idea how that square root actually gets computed.
- That’s because we understand what a square root is.
When we start actually writing the code, we implement a procedural abstraction by
-
assigning an appropriately named “function” to represent that procedural abstraction,
-
in the “main” code, calling that function, trusting that it will actually do what we want but not worrying about how it will do it, and
-
finally, writing a function body using an appropriate algorithm to do what we want.
In practice, there may be many algorithms to achieve the same abstraction, and we use engineering considerations such as speed, memory requirements, and ease of implementation to choose among the possibilities.
For example, the “sqrt” function is probably implemented using a technique completely unrelated to any technique you may have learned in grade school for computing square roots. On many systems. sqrt doesn’t compute a square root at all, but computes a polynomial function that was chosen as a good approximation to the actual square root and that can be evaluated much more quickly than an actual square root. It may then refine the accuracy of that approximation by applying Newton’s method, a technique you may have learned in Calculus.
Does it bother you that sqrt does not actually compute via a square root algorithm? Probably not. It shouldn’t. As long as we trust the results, the method is something we are happy to ignore.
1.2 Data Abstraction
Data abstraction works much the same way.
A data abstraction is a mental model of what can be done to a collection of data. It deliberately excludes details of how to do it.
Example: calendar days
A day (date?) in a calendar denotes a 24-hour period, identified by a specific year, month, and day number.
That’s it. That’s probably all you need to know for you and I to agree that we are talking about a common idea.
One of the running examples used throughout this course is the design and implementation of a spreadsheet.
Example: cell names
Every cell in a spreadsheet has a unique name. The name has a column part and a row part.
-
The row indicators are integer values starting at 1.
-
The column indicators are case-insensitive strings of alphabetic characters as follows:
A,B, … ,Z,AA,AB,AC, … ,AZ,BA,BB, …ZZ,AAA,AAB, … and so on. -
Optional
$markers may appear in front of each part to “fix” the row or column during copying.
For example, suppose we have a cell B1 containing the formula 2*A1 and that we copy and paste that cell to position C3. When we look in C3, we would find the pasted formula was 2*B3 adjusted for the number of rows and columns over which we moved the copied value.
But if the cell B1 originally contained the formula 2*A$1, the copied formula would be 2*B$1. The $ indicates that we are fixing the column indicator during copies. Similarly, if the cell B1 originally contained the formula 2*$A$1, the copied formula would be 2*$A$1. (If this isn’t clear, fire up a spreadsheet and try it. We can’t expect to share mental models (abstractions) if we don’t share an experience with the subject domain.)
Example: a book
How to describe a book?
-
If we are implementing a card catalog and library checkout, it is probably enough to list the metadata
-
(e.g., title, authors, publisher, date).
-
-
If, however, we are going to be working on a project involving the full text of the document (e.g., automatic metadata extraction and indexing), then we might need all the pages and all the text.
-
Of course, if we were building bookshelves, we might need more physical attributes such as size and weight!
Example: positions within a container
Many of the abstractions that we work with are “containers” of arbitrary numbers of pieces of other data.
Any time you have an ordered sequence of data, you can imagine the need to look through it. That then leads to the concept of a position within that sequence, with notions like
- finding the first and last position,
- going forward to the next position, etc.
2 Abstract Data Types
Adding Interfaces
-
The mental model offered by a data abstraction gives us an informal understanding of how and when to use it.
-
But because it is simply a mental model, it does not tell us enough information to program with it.
-
An abstract data type (ADT) captures this model in a programming language interface.
Definition of an Abstract Data Type
(traditional): An abstract data type (ADT) is a type name and a list of operations on that type.
It’s convenient, for the purpose of this course, to modify this definition just slightly:
Definition (alternate): An abstract data type (ADT) is a type name and a list of members (data or function) on that type.
- an ADT corresponds, more or less, to the public portion of a typical class
- the “list of members” includes
- names
- data types
- expected behavior
- a.k.a. an ADT specification
This change is not really all that significant. Traditionally, a data member X is modeled as a pair of getX() and putX(x) (or ’setX(x)) functions. But in practice, we will allow ADTs to include data members in their specification. This definition may make it a bit clearer that an ADT corresponds, more or less, to the public portion of a typical class.
In either case, when we talk about listing the members, this includes giving their names and their data types (for functions, their return types and the data types of their parameters).
If you search the web for the phrase “abstract data type”, you’ll find lots of references to stacks, queues, etc. - the “classic” data structures. Certainly, these are ADTs. But, just as with the abstractions introduced earlier, each application domain has certain characteristic or natural abstractions that may also need programming interfaces.
ADT Members: attributes and operations
Commonly divided into
-
attributes: the things that we think of as being data stored inthe ADT
- Actual interface is often through getAttr() and setAttr() functions.
- which, in turn, might or might not actually involve direct access to a “data member”
-
operations: the functions or behaviors or the ADT
- the “type” of a function consists of its return type and an ordered list of of its parameters’ types
2.1 Examples
2.1.1 Calendar Days
Nothing in the definition of ADT that says that the interface has to be written out in a programming language.
UML diagrams present classes as a 3-part box: name, attributes, & operations
2.1.2 Calendar Days: Alternative
But we can use a more programming-style interface:
class Day {
public:
// Attributes
int getDay();
void setDay (int);
int getMonth();
void setMonth(int);
int getYear();
void setYear(int);
// Operations
Day operator+ (int numDays);
int operator- (Day);
bool operator< (Day);
bool operator== (Day);
⋮
Notations
class Day {
public:
// Attributes
int getDay();
void setDay (int);
int getMonth();
void setMonth(int);
int getYear();
void setYear(int);
// Operations
Day operator+ (int numDays);
int operator- (Day);
bool operator< (Day);
bool operator== (Day);
⋮
- Disadvantages of moving early to programming-style interfaces:
- getting lost in language details
- prematurely committing to those details
2.1.3 Cell Names
Here is a possible interface for our cell name abstraction.
class CellName
{
public:
CellName (std::string column, int row,
bool fixTheColumn = false,
bool fixTheRow=false);
//pre: column.size() > 0 && all characters in column are alphabetic
// row > 0
CellName (std::string cellname);
//pre: exists j, 0<=j<cellname.size()-1,
// cellname.substr(0,j) is all alphabetic (except for a
// possible cellname[0]=='$')
// && cellname.substr(j) is all numeric (except for a
// possible cellname[j]=='$') with at least one non-zero
// digit
CellName (unsigned columnNumber = 0, unsigned rowNumber = 0,
bool fixTheColumn = false,
bool fixTheRow=false);
std::string toString() const;
// render the entire CellName as a string
// Get components in spreadsheet notation
std::string getColumn() const;
int getRow() const;
bool isRowFixed() const;
bool isColumnFixed() const;
// Get components as integer indices in range 0..
int getColumnNumber() const;
int getRowNumber() const;
bool operator== (const CellName& r) const
⋮
private:
⋮
Arguably, the diagram presents much the same information as the code
2.1.4 Example: A Book
If we were to try to capture our book abstraction (concentrating on the metadata), we might come up with something like:
class Book {
public:
Book (Author) // for books with single authors
Book (Author[], int nAuthors) // for books with multiple authors
std::string getTitle() const;
void putTitle(std::string theTitle);
int getNumberOfAuthors() const;
std::string getIsBN() const;
void putISBN(std::string id);
Publisher getPublisher() const;
void putPublisher(const Publisher& publ);
AuthorPosition begin();
AuthorPosition end();
void addAuthor (AuthorPosition at, const Author& author);
void removeAuthor (AuthorPosition at);
private:
⋮
};
- What are
AuthorandPublisherin this interface?- They are simply other ADTs in this library world, and will need to have designed interfaces of their own.
2.1.5 Example: Positions within a Container
Coming up with a good interface for our position abstraction is a problem that has challenged many an ADT designer.
- A look at our
Bookinterface may suggest why.
class Book {
public:
Book (Author) // for books with single authors
Book (Author[], int nAuthors) // for books with multiple authors
std::string getTitle() const;
void putTitle(std::string theTitle);
int getNumberOfAuthors() const;
std::string getIsBN() const;
void putISBN(std::string id);
Publisher getPublisher() const;
void putPublisher(const Publisher& publ);
typedef int AuthorPosition;
<+1>Author getAuthor (AuthorPosition authorNum) const; <-1>
void addAuthor (AuthorPosition at, const Author& author);
void removeAuthor (AuthorPosition at);
private:
⋮
};
- One intuitive idea might be to simply number the authors and treat the number as a position indicator, as shown here.
Iterators
The solution adapted by the C++ community is to have every ADT that is a “container” of sequences of other data to provide a special type for positions within that sequence.
- The container itself provides functions to return
- the beginning position in the sequence and
- the position just after the last data item in the
begin()andend()
- The position ADT must provide, at a minimum:
-
A function to fetch the data item at the given position.
-
A function to advance from the current position to the next position in the sequence.
-
A function to compare two positions to see if they are the same.
-
A Possible Position Interface
In theory, we could satisfy this requirement with an ADT like this:
class AuthorPosition {
public:
AuthorPosition();
// get data at this position
Author getData() const;
// get the position just after this one
AuthorPosition next() const;
// Is this the same position as pos?
bool operator== (const AuthorPosition& pos) const;
bool operator!= (const AuthorPosition& pos) const;
};
which in turn would allow us to access authors like this:
void listAllAuthors(Book& b)
{
for (AuthorPosition p = b.begin(); p != b.end();
p = p.next())
cout << "author: " << p.getData() << endl;
}
The Iterator ADT
For historical reasons (and brevity), however, C++ programmers use overloaded operators for the getData() and next() operations:
class AuthorPosition {
public:
AuthorPosition();
// get data at this position
Author operator*() const;
// get a data/function member at this position
Author* operator->() const;
// move forward to the position just after this one
AuthorPosition operator++();
// Is this the same position as pos?
bool operator== (const AuthorPosition& pos) const;
bool operator!= (const AuthorPosition& pos) const;
};
so that code to access authors would look like this:
void listAllAuthors(Book& b)
{
for (AuthorPosition p = b.begin(); p != b.end();
++p)
cout << "author: " << *p << endl;
}
This ADT for positions is called an iterator (because it lets us iterate over a collection of data).
2.2 Design Patterns
Iterator as a Design Pattern
The idea of an iterator is an instance of what we call a design pattern:
- a reusable concept that is not so much a piece of code as it is a design idea.
Pattern, not ADT
In C++, our application code does not actually work with an actual ADT named “Iterator”.
-
Instead, we typically have a lot of different ADTs, all of which share the common pattern of supporting an operator
++to move forward, an operator*for fetching a value at the position, etc. -
Each of these iterator ADTs is related to some kind of collection of data.
- These collections have nothing to do with one another except that they share the common idea of supplying
begin()andend()functions to provide the beginning and ending position within that collection.
- These collections have nothing to do with one another except that they share the common idea of supplying
Realizing a Design Pattern
-
Iterator and Collection are general patterns for interfaces.
-
We will have many actual classes that are unrelated to one another but that implement or realize those patterns.
- Such classes are called concrete realizations of the general patterns.
- It’s these concrete classes that our application actually works with.
3 ADTs as contracts
ADTs as contracts
An ADT represents a contract between the ADT developer and the users (application programmers).
The Contract
Application writers (the “users” of the ADT) are expected to alter/examine values of this type only via the operations and members provided.
The creator of the ADT promises to leave the operation specifications unchanged.
The creator of the ADT is allowed to change the code of the operations at any time, as long as it continues to satisfy the specifications.
The creator of the ADT is also allowed to change the data structure actually used to implement the type.
Why the Contract
What do we gain by holding ourselves to this contract?
- Application programmers can be designing and even implementing the application before the details of the ADT implementation have been worked out. This helps in
- top-down design
- development by teams
- The ADT implementors knows exactly what they must provide and what they are allowed to change.
- ADTs designed in this manner are often re-usable. By reusing code, we save time in
- implementation
- debugging
- We gain the flexibility to try/substitute different data structures to actually implement the ADT, without needing to alter the application code.
- By encouraging modularity, application code becomes more readable.
3.1 Information Hiding
Information Hiding
Every design can be viewed as a collection of “design decisions”.
-
David Parnas formulated the principle: “Every module [procedure] should be designed so as to hide one design decision from the rest of the program.”
-
He argued that such information hiding made future changes more economical.
Encapsulation
Although ADTs can be designed without language support, they rely on programmers’ self-discipline for enforcement of information hiding.
Encapsulation is the enforcement of information hiding by programming language constructs.
4 ADT Implementations
ADT Implementations
An ADT is implemented by supplying
-
a data structure for the type name.
-
coded algorithms for the operations.
We sometimes refer to the ADT itself as the ADT specification or the ADT interface, to distinguish it from the code of the ADT implementation.
In C++, implementation is generally done using a C++ class.
- Uses public/private to enforce the ADT contract
4.1 Examples
4.2 Calendar Day Implementations
As ADT designer, I might consider two possible data structures:
- store the month, day, & year as integers:
class Day
{
/**
Represents a day with a given year, month, and day
of the Gregorian calendar. The Gregorian calendar
replaced the Julian calendar beginning on
October 15, 1582
*/
public:
Day(int aYear, int aMonth, int aDate);
/**
Returns the year of this day
@return the year
*/
int getYear() const;
/**
Returns the month of this day
@return the month
*/
int getMonth() const;
/**
Returns the day of the month of this day
@return the day of the month
*/
int getDate() const;
/**
Returns a day that is a certain number of days away from
this day
@param n the number of days, can be negative
@return a day that is n days away from this one
*/
Day addDays(int n) const;
/**
Returns the number of days between this day and another
day
@param other the other day
@return the number of days that this day is away from
the other (>0 if this day comes later)
*/
int daysFrom(Day other) const;
enum Months {JANUARY = 1,
FEBRUARY = 2,
MARCH = 3,
APRIL = 4,
MAY = 5,
JUNE = 6,
JULY = 7,
AUGUST = 8,
SEPTEMBER = 9,
OCTOBER = 10,
NOVEMBER = 11,
DECEMBER = 12};
private:
/**
Compares this day with another day.
@param other the other day
@return a positive number if this day comes after the
other day, a negative number if this day comes before
the other day, and zero if the days are the same
*/
int compareTo(Day other) const;
/**
Computes the next day.
@return the day following this day
*/
Day nextDay() const;
/**
Computes the previous day.
@return the day preceding this day
*/
Day previousDay() const;
/**
Gets the days in a given month
@param y the year
@param m the month
@return the last day in the given month
*/
static int daysPerMonth(int y, int m);
/**
Tests if a year is a leap year
@param y the year
@return true if y is a leap year
*/
static bool isLeapYear(int y);
int year;
int month;
int date;
static const int DAYS_PER_MONTH [12];
// = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
static const int GREGORIAN_START_YEAR = 1582;
static const int GREGORIAN_START_MONTH = 10;
static const int GREGORIAN_START_DAY = 15;
static const int JULIAN_END_DAY = 4;
};
/**
Day class
copyright Steven J Zeil, 2003, based upon
Day.java from Cay Horstmann's "Object-Oriented Design & Patterns"
**/
#include "day.h"
using namespace std;
const int Day::DAYS_PER_MONTH [12]
= { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
/**
Constructs a day with a given year, month, and day
of the Julian/Gregorian calendar. The Julian calendar
is used for all days before October 15, 1582
@param aYear a year != 0
@param aMonth a month between 1 and 12
@param aDate a date between 1 and 31
*/
Day::Day(int aYear, int aMonth, int aDate)
{
year = aYear;
month = aMonth;
date = aDate;
}
/**
Returns the year of this day
@return the year
*/
int Day::getYear() const
{
return year;
}
/**
Returns the month of this day
@return the month
*/
int Day::getMonth() const
{
return month;
}
/**
Returns the day of the month of this day
@return the day of the month
*/
int Day::getDate() const
{
return date;
}
/**
Returns a day that is a certain number of days away from
this day
@param n the number of days, can be negative
@return a day that is n days away from this one
*/
Day Day::addDays(int n) const
{
Day result = *this;
while (n > 0)
{
result = result.nextDay();
n--;
}
while (n < 0)
{
result = result.previousDay();
n++;
}
return result;
}
/**
Returns the number of days between this day and another
day
@param other the other day
@return the number of days that this day is away from
the other (>0 if this day comes later)
*/
int Day::daysFrom(Day other) const
{
int n = 0;
Day d = *this;
while (d.compareTo(other) > 0)
{
d = d.previousDay();
n++;
}
while (d.compareTo(other) < 0)
{
d = d.nextDay();
n--;
}
return n;
}
/**
Compares this day with another day.
@param other the other day
@return a positive number if this day comes after the
other day, a negative number if this day comes before
the other day, and zero if the days are the same
*/
int Day::compareTo(Day other) const
{
if (year > other.year) return 1;
if (year < other.year) return -1;
if (month > other.month) return 1;
if (month < other.month) return -1;
return date - other.date;
}
/**
Computes the next day.
@return the day following this day
*/
Day Day::nextDay() const
{
int y = year;
int m = month;
int d = date;
if (y == GREGORIAN_START_YEAR
&& m == GREGORIAN_START_MONTH
&& d == JULIAN_END_DAY)
d = GREGORIAN_START_DAY;
else if (d < daysPerMonth(y, m))
d++;
else
{
d = 1;
m++;
if (m > DECEMBER)
{
m = JANUARY;
y++;
if (y == 0) y++;
}
}
return Day(y, m, d);
}
/**
Computes the previous day.
@return the day preceding this day
*/
Day Day::previousDay() const
{
int y = year;
int m = month;
int d = date;
if (y == GREGORIAN_START_YEAR
&& m == GREGORIAN_START_MONTH
&& d == GREGORIAN_START_DAY)
d = JULIAN_END_DAY;
else if (d > 1)
d--;
else
{
m--;
if (m < JANUARY)
{
m = DECEMBER;
y--;
if (y == 0) y--;
}
d = daysPerMonth(y, m);
}
return Day(y, m, d);
}
/**
Gets the days in a given month
@param y the year
@param m the month
@return the last day in the given month
*/
int Day::daysPerMonth(int y, int m)
{
int days = DAYS_PER_MONTH[m - 1];
if (m == FEBRUARY && isLeapYear(y))
days++;
return days;
}
/**
Tests if a year is a leap year
@param y the year
@return true if y is a leap year
*/
bool Day::isLeapYear(int y)
{
if (y % 4 != 0) return false;
if (y < GREGORIAN_START_YEAR) return true;
return (y % 100 != 0) || (y % 400 == 0);
}
- store a single integer, indicating # of days since some fixed date
/**
Day class
copyright Steven J Zeil, 2003, based upon
Day.java from Cay Horstmann's "Object-Oriented Design & Patterns"
**/
class Day
{
/**
Constructs a day with a given year, month, and day
of the Julian/Gregorian calendar. The Julian calendar
is used for all days before October 15, 1582
@param aYear a year != 0
@param aMonth a month between 1 and 12
@param aDate a date between 1 and 31
*/
public:
Day(int aYear, int aMonth, int aDate);
/**
Returns the year of this day
@return the year
*/
int getYear() const;
/**
Returns the month of this day
@return the month
*/
int getMonth() const;
/**
Returns the day of the month of this day
@return the day of the month
*/
int getDate() const;
/**
Returns a day that is a certain number of days away from
this day
@param n the number of days, can be negative
@return a day that is n days away from this one
*/
Day addDays(int n) const;
/**
Returns the number of days between this day and another
day
@param other the other day
@return the number of days that this day is away from
the other (>0 if this day comes later)
*/
int daysFrom(Day other) const;
enum Months {JANUARY = 1,
FEBRUARY = 2,
MARCH = 3,
APRIL = 4,
MAY = 5,
JUNE = 6,
JULY = 7,
AUGUST = 8,
SEPTEMBER = 9,
OCTOBER = 10,
NOVEMBER = 11,
DECEMBER = 12};
private:
/**
Computes the Julian day number of the given day.
@param year a year
@param month a month
@param date a date
@return The Julian day number that begins at noon of
the given day
Positive year signifies CE, negative year BCE.
Remember that the year after 1 BCE was 1 CE.
*/
static int getJulian(int year, int month, int date);
struct CalDate {
int year;
int month;
int date;
};
/**
Converts a Julian day number to a calendar date.
@param j the Julian day number
@return a structure containing the year, month,
and day of the month.
*/
static CalDate fromJulian(int j);
Day (int julianDate);
int julian;
};
/**
Day class
copyright Steven J Zeil, 2003, based upon
Day.java from Cay Horstmann's "Object-Oriented Design & Patterns"
**/
#include "day.h"
using namespace std;
/**
Constructs a day with a given year, month, and day
of the Julian/Gregorian calendar. The Julian calendar
is used for all days before October 15, 1582
@param aYear a year != 0
@param aMonth a month between 1 and 12
@param aDate a date between 1 and 31
*/
Day::Day(int aYear, int aMonth, int aDate)
{
julian = toJulian(aYear, aMonth, aDate);
}
/**
Constructs a day with a Julian date.
@param julianDate a valid Julian date
*/
Day::Day(int julianDate)
: julian(julianDate)
{
}
/**
Returns the year of this day
@return the year
*/
int Day::getYear() const
{
return fromJulian(julian).year;
}
/**
Returns the month of this day
@return the month
*/
int Day::getMonth() const
{
return fromJulian(julian).month;
}
/**
Returns the day of the month of this day
@return the day of the month
*/
int Day::getDate() const
{
return fromJulian(julian).date;
}
/**
Returns a day that is a certain number of days away from
this day
@param n the number of days, can be negative
@return a day that is n days away from this one
*/
Day Day::addDays(int n) const
{
return Day(julian + n);
}
/**
Returns the number of days between this day and another
day
@param other the other day
@return the number of days that this day is away from
the other (>0 if this day comes later)
*/
int Day::daysFrom(Day other) const
{
return julian - other.julian;
}
/**
Computes the Julian day number of the given day.
@param year a year
@param month a month
@param date a date
@return The Julian day number that begins at noon of
the given day
Positive year signifies CE, negative year BCE.
Remember that the year after 1 BCE was 1 CE.
A convenient reference point is that May 23, 1968 noon
is Julian day number 2440000.
Julian day number 0 is a Monday.
This algorithm is from Press et al., Numerical Recipes
in C, 2nd ed., Cambridge University Press 1992
*/
int Day::toJulian(int year, int month, int date)
{
int jy = year;
if (year < 0) jy++;
int jm = month;
if (month > 2) jm++;
else
{
jy--;
jm += 13;
}
int jul = (int) (int(365.25 * jy)
+ int(30.6001*jm) + date + 1720995.0);
int IGREG = 15 + 31*(10+12*1582);
// Gregorian Calendar adopted Oct. 15, 1582
if (date + 31 * (month + 12 * year) >= IGREG)
// change over to Gregorian calendar
{
int ja = (int)(0.01 * jy);
jul += 2 - ja + (int)(0.25 * ja);
}
return jul;
}
/**
Converts a Julian day number to a calendar date.
This algorithm is from Press et al., Numerical Recipes
in C, 2nd ed., Cambridge University Press 1992
@param j the Julian day number
@return an array whose 0 entry is the year, 1 the month,
and 2 the day of the month.
*/
Day::CalDate Day::fromJulian(int j)
{
int ja = j;
int JGREG = 2299161;
/* the Julian day number of the adoption of the Gregorian
calendar
*/
if (j >= JGREG)
/* cross-over to Gregorian Calendar produces this
correction
*/
{
int jalpha = (int)(((float)(j - 1867216) - 0.25)
/ 36524.25);
ja += 1 + jalpha - (int)(0.25 * jalpha);
}
int jb = ja + 1524;
int jc = (int)(6680.0 + ((float)(jb-2439870) - 122.1)
/365.25);
int jd = (int)(365 * jc + (0.25 * jc));
int je = (int)((jb - jd)/30.6001);
int date = jb - jd - (int)(30.6001 * je);
int month = je - 1;
if (month > 12) month -= 12;
int year = jc - 4715;
if (month > 2) --year;
if (year <= 0) --year;
return (CalDate) { year, month, date };
}
Each approach has pros and cons.
4.3 CellName Implementation
class CellName
{
public:
CellName (std::string column, int row,
bool fixTheColumn = false,
bool fixTheRow=false);
//pre: column.size() > 0 && all characters in column are alphabetic
// row > 0
CellName (std::string cellname);
//pre: exists j, 0<=j<cellname.size()-1,
// cellname.substr(0,j) is all alphabetic (except for a
// possible cellname[0]=='$')
// && cellname.substr(j) is all numeric (except for a
// possible cellname[j]=='$') with at least one non-zero
// digit
CellName (unsigned columnNumber = 0, unsigned rowNumber = 0,
bool fixTheColumn = false,
bool fixTheRow=false);
std::string toString() const;
// render the entire CellName as a string
// Get components in spreadsheet notation
std::string getColumn() const;
int getRow() const;
bool isRowFixed() const;
bool isColumnFixed() const;
// Get components as integer indices in range 0..
int getColumnNumber() const;
int getRowNumber() const;
bool operator== (const CellName& r) const
{return (columnNumber == r.columnNumber &&
rowNumber == r.rowNumber &&
theColIsFixed == r.theColIsFixed &&
theRowIsFixed == r.theRowIsFixed);}
private:
⋮
int rowNumber;
bool theRowIsFixed;
bool theColIsFixed;
int CellName::alphaToInt (std::string columnIndicator) const;
std::string CellName::intToAlpha (int columnIndex) const;
};
inline
bool CellName::isRowFixed() const {return theRowIsFixed;}
inline
bool CellName::isColumnFixed() const {return theColIsFixed;}
#endif
There are some options here the have not been explored:
- Do we want the column info stored as a number, a string, or both?
4.4 Book Implementation
We can implement Book in book.h:
#ifndef BOOK_H
#include "author.h"
#include "publisher.h"
class Book {
public:
typedef const Author* AuthorPosition;
Book (Author); // for books with single authors
Book (const Author[], int nAuthors); // for books with multiple authors
std::string getTitle() const;
void setTitle(std::string theTitle);
int getNumberOfAuthors() const;
std::string getISBN() const;
void setISBN(std::string id);
Publisher getPublisher() const;
void setPublisher(const Publisher& publ);
AuthorPosition begin() const;
AuthorPosition end() const;
void addAuthor (AuthorPosition at, const Author& author);
void removeAuthor (AuthorPosition at);
private:
std::string title;
int numAuthors;
std::string isbn;
Publisher publisher;
static const int MAXAUTHORS = 12;
Author authors[MAXAUTHORS];
};
#endif
and in book.cpp:
#include "book1.h"
// for books with single authors
Book::Book (Author a)
{
numAuthors = 1;
authors[0] = a;
}
// for books with multiple authors
Book::Book (const Author au[], int nAuthors)
{
numAuthors = nAuthors;
for (int i = 0; i < nAuthors; ++i)
{
authors[i] = au[i];
}
}
std::string Book::getTitle() const
{
return title;
}
void Book::setTitle(std::string theTitle)
{
title = theTitle;
}
int Book::getNumberOfAuthors() const
{
return numAuthors;
}
std::string Book::getISBN() const
{
return isbn;
}
void Book::setISBN(std::string id)
{
isbn = id;
}
Publisher Book::getPublisher() const
{
return publisher;
}
void Book::setPublisher(const Publisher& publ)
{
publisher = publ;
}
Book::AuthorPosition Book::begin() const
{
return authors;
}
Book::AuthorPosition Book::end() const
{
return authors+numAuthors;
}
void Book::addAuthor (Book::AuthorPosition at, const Author& author)
{
int i = numAuthors;
int atk = at - authors;
while (i >= atk)
{
authors[i+1] = authors[i];
i--;
}
authors[atk] = author;
++numAuthors;
}
void Book::removeAuthor (Book::AuthorPosition at)
{
int atk = at - authors;
while (atk + 1 < numAuthors)
{
authors[atk] = authors[atk + 1];
++atk;
}
--numAuthors;
}