Programming in the small, medium, large You must be able to write - - PowerPoint PPT Presentation

Duke CPS 108

• 6. 1

Programming in the small, medium, large

• You must be able to write itoa to be able to write hyperwag
• You must understand the difference between a pointer and a

reference to write hyperwag

• You must know about templates, copy constructors, arrays,

pointers to functions to write igloo (whatever it is)

• You must know about built-in arrays and c-style strings to be able

to implement a string and vector class, or be able to cope without them

• You must know about factories and proxies to design and

implement using object-oriented principles

• You must know about patterns to communicate

Duke CPS 108

• 6. 2

Classes, compilers, dependencies

#include <string> #include “day.h” typedef string TimeRange; class ostream; class Appointment { public: TimeRange duration(); void print(ostream & output); private: Day myDay; };

• why use class ostream instead of #include <stream>
• what is a typedef and how is it used?
• make depend for Appointment/ostream?
• changes to Day force recompile for appointment clients?

Duke CPS 108

• 6. 3

.h guidelines, the preprocessor in action

• minimize #includes in every .h file

➤ avoid circular dependencies ➤ avoid re-compile by minimizing dependencies

• class Foo in foo.h, class Bar in bar.h, client foobar.cpp

#ifndef _FOO_H #ifndef _BAR_H #define _FOO_H #define _BAR_H #include “bar.h” #include “foo.h” class Foo class Bar { { Bar getBar(); Foo getFoo(); // from foo.cpp #include “bar.h” #include “foo.h” void Foo::doStuff(const Bar & b)...

• Avoid #includes, use forward references, sometimes you must do

this as shown above (even if you don’t want to)

Duke CPS 108

• 6. 4

#include “foo.h”

• will be needed in .cpp file, e.g., foo.cpp and bar.cpp
• using pointers and references in .h files minimizes dependencies

➤ minimize recompiles when .h changes ➤ loose coupling: avoid implementation dependencies when

possible

• avoid letting implementation leek into public view

➤ what about private section? ➤ opaque pointer: FooImpl * myImpl;

• implementation of FooImpl is hidden, class can be

implemented in foo.cpp (handle-body idiom)

➤ factory: inheritance hierarchy, ABC (more later)

Duke CPS 108

• 6. 5

Has-a vs. has-a-pointer to

• benefits of string * myName vs string myName?
• downside of using pointers?
• responsibilities for memory management, garbage collection

➤ it that news, deletes, not always possible ➤ use proxy class, stands in for pointer (Pstring) ➤ deletes cause bugs, introduce destructors into the system

iteratively, chasing one bug at a time

• pointers and references are the same size, both allow one variable

to refer to memory created/stored elsewhere

➤ reference values bound on construction, no change ➤ pointer values can be changed

Duke CPS 108

• 6. 6

The best IO is no IO

• See the programs wcget.cpp, wcplus.cpp, wcplus2.cpp

➤ if you only need to count words, avoid storing them ➤ if you need to store words what can you do?

• Strings are wrappers around char * strings (later)
• Strings can be “smart” use pool of constants to save storage,

use lazy copy/ assignment aka copy on write

➤ What interface do you program to?

• The Adapter pattern (aka Wrapper)

➤ Use when interface doesn’t match what you need, e.g.,

Init/Next iterator used in STL context (iteradapter.h)

➤ What are templated classes, how do they work?