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Classes, compilers, dependencies

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.h>

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Classes, compilers, dependencies

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  1. 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.h> • what is a typedef and how is it used? • make depend for Appointment/ostream? • changes to Day force recompile for appointment clients?

  2. .h guidelines, 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)

  3. #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

  4. Microsoft question, 108 question • Write atoi, write itoa, which is harder? • Questions? Issues? Problems? int atoi(const char * sp); char * itoa(int num); string itoa(int num); string uitoa(unsigned int num); // what’s the difference? • Difference between const char * p and char * const p • one is a pointer to a constant character • one is a constant pointer to a character

  5. What’s hard about itoa (or atoi)? • What’s the naïve way of coding itoa? • Performance implications? • Alternatives? • What does the standard do? • What’s the naïve way of coding atoi? • Where can problems happen? • What are choices for dealing with them? • What does the standard do? • What will you do?

  6. What about ints and unsigned ints? • What are the largest and smallest integer values? • Where defined? What is standard? What is common? • Typically we have fabs(INT_MIN) > fabs(INT_MAX) • Typically –INT_MIN is negative • What does this depend on? Do we need to be aware of this? • Two’s complement is nearly universal • Unsigned values are your friends int x = INT_MIN; x = -x; unsigned int y = -x;

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