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COMP2004
Programming Practice
2002 Summer School


Kevin Pulo
School of Information Technologies
University of Sydney

Exam information

• Location:MacLaurin Hall,

Main Quadrangle

• Duration:2 hrs (10 mins reading)
• Date:Friday 15 February 2002
• Time:9:20am to 11:30am
• Format:Closed book

• Clash => see or email me ASAP

Course Overview

• Basic C++
• Object-oriented C++
• Unix development tools
• Advanced C++
• C++ Standard Template Library (STL)

Course Overview

• Basic C++
  • Simple syntax, input/output, strings, vectors, etc
  • Pointers, arrays, memory allocation

• Object-oriented C++
  • Classes, operator overloading
  • Inheritance, namespaces

• Unix development tools
  • Shell, make, gdb, revision control

Course Overview

• Advanced C++
  • Generic code
  • Exceptions and exception safety
  • String streams

• C++ Standard Template Library (STL)
  • Iterators, containers
  • Function objects, algorithms

Basic C++

• IO (input / output)
  • Buffered / unbuffered, cout / cerr
• Manipulators
  • cout << setw(10) << 42;
• Strings
  • All obvious operators work
    • s[0], +, +=, ==, <, etc
  • Convert from C-style
    • char *c = "hello"; string s(c);
  • Convert to C-style
    • s.c_str()

Passing parameters

• Pass by value
  • void func(int value)
  • Copies values
• Pass by reference
  • void func(int& value)
  • Direct access to original object
• Pass by const reference
  • void func(const int& value)
  • Direct access, but no changes allowed

Pointers

int main() {
int i = 42;
int *p = &i;
*p = 3;
p = NULL;
if (p)
cout << *p << endl;
}

Arrays

int main() {
int a[10];
int b[ ] = { 1, 2, 3 };
char c[ ] = "a c-style string";
char *d = c;

a[3] = b[1];
cout << *c << *d << endl;
d += 3;
cout << d[1] << *(c + 4) << endl;
}

Arguments to main()

int main(int argc, char **argv) {
if (argc >= 3) {
cout << argv[2] << endl;
}
}

bash$ prog These are the args the

Memory Allocation

• Automatic - Local variables
  • Exist only during local scope

• Static
  • Global variables
  • Static local variables
  • Exist from program start to finish

• Dynamic - new and delete
  • Exist between explicit creation and destruction

Memory Leaks

• Every new needs a corresponding delete

int main() {
int *data = new int(4);
data = new int(12);
data = new int(42);
delete data;
}

Object-oriented C++

• Structs and classes
  • Structs default to public
  • Classes default to private

Student s;
Student *sp = &s;
s.sid = "9222194";
sp->courses.push_back("comp2004");

Example minimal class

class A {
public:
A();
A(const A& o);
~A();
A& operator=(const A& o) {
if (this == &o) return *this;
...
}
};

Const correctness

class List {
int length() const;
void clear();
}

• length() method cannot modify object
• const reference cannot call non-const method
  • const List &l;

l.clear(); // not allowed

Operator overloading

• Makes classes act like built-in types
• Eg: output operator:
• ostream& operator<<(ostream &os,

const List& list) {
...
return os;
}

Type conversions

• Other to List:
  • List::List(const string &s)
  • Used to convert string to List

• List to other:
  • List::operator bool() const
  • Used to convert List to bool
  • Return type obviously bool

Inheritance

• class BuzzerAlarm : public Alarm {

...
};

• Don't pass base class objects by value:
  • void activate(Alarm a)
• The copying causes slicing
• Pass (const) reference instead:
  • void activate(Alarm& a)
  • void activate(const Alarm& a)

Accessibility

• public members visible to all
• private members hidden from children
• protected members visible to children, but still hidden from others

• Use public to provide interface to others
• Use protected to provide interface to children

Virtual methods

void activate(Alarm& a) {
a.turn_on();
}
BuzzerAlarm b;
activate(b);

• If turn_on() is not virtual:
  • Calls turn_on() in Alarm
• If turn_on() is virtual:
  • Calls turn_on() in BuzzerAlarm
• Virtual methods require virtual destructor

Pure virtual methods

class Alarm {
virtual void turn_on() = 0;
};

• Alarm is abstract
  • Cannot create Alarm objects
• Child classes must redefine turn_on()

Namespaces

namespace lib {
string func() { ... }
}

cout << lib::func() << endl;
using namespace lib;
cout << func() << endl;


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