Plan Review of variable types C++: Tour 2 Functions But first - PDF document

Plan • Review of variable types C++: Tour 2 • Functions But first… Projects • UML tidbits • Any questions? – Use cases – please include documentation – Associations vs. Attributes • Design due March 28 th – Seq Diagrams in Logical View – Online docs of shapewin library on Web – Can include shapewin classes in UML • Partners…anyone doesn’t have one? Finally… Variables in C++ • Special thanks to Prof Swammi for taking • Variable types my lecture on Thursday – Basic – Pointer – Reference • Any questions?

Variables in C++ Variables in C++ • Basic variable Basic variable – Memory associated with a variable with size int foo; based on the type of the variable. float f = 7.0; – Variable declarations are “executable” statements Student joe (“Geigel” , “Joe”, “GCCIS”, • Memory is allocated when declaration is made “CS”); – No need to use new when instantiating objects of a class. Variables in C++ Variables in C++ • Assignment = copy not reference • Assignment = copy not reference – In Java – In C++ • Student joe = new Student(“Geigel” , “Joe”, • Student joe (“Geigel” , “Joe”, “GCCIS”, “CS”); “GCCIS”, “CS”); • Student fred = joe; • Student fred = joe; joe Joe joe Joe Geigel Geigel fred fred Joe Geigel Variables in C++ Variables in C++ • Basic variable • Pointer Variables – Accessing class members – Stores the memory address of an object. • Uses the . Syntax used in Java – new returns a pointer to an object and allocates memory for it on the heap (free store). • Student joe (“Geigel” , “Joe”, “GCCIS”, “CS”); – Can have pointers to basic data types. • joe.getGrades(); – C++ has no garbage collection! – NULL pointer takes value 0.

Variables in C++ Variables in C++ • Pointer Variables Pointer variable – Dereference operator * – If ptr is a pointer int *foo; float *f = 7.0; // Invalid • i.e A variable whose contents is a memory address – then *ptr refers to the object or data item that float *g = 0; // okay is pointed to by ptr float *h = 0x12345; // actually illegal!! • Can be interpreted as: – The data item or object at ptr Student *joe = new Student (“Geigel” , – The object or data item pointed to by ptr “Joe”, “GCCIS”, “CS”); Variables in C++ Variables in C++ Pointer variable • Address of operator – You can always get the address of any variable float *f = 7.0; // Invalid however or object by using the address of operator &. float *f = new float; • float f = 7.0; • float *fptr = &f; (*f) = 7.0; – Use with caution!! Student *joe = new Student (“Geigel” , • Student joe (“Geigel” , “Joe”, “GCCIS”, “CS”); “Joe”, “GCCIS”, “CS”); • Student *joeptr = &joe; Student *fred = joe; Variables in C++ Variables in C++ • Pointer variable • Assignment = copy not reference – Accessing class members – For Pointer Variables as well • Uses the -> Syntax • Student *joe = new Student(“Geigel” , “Joe”, “GCCIS”, “CS”); • Student *fred = joe; • Student *joe = new Student (“Geigel” , “Joe”, “GCCIS”, “CS”); • joe->getGrades(); 0x345ABC2 joe 0x345ABC2 Joe • Which is the same as Geigel fred 0x345ABC2 • (*joe).getGrades();

Variables in C++ Variables in C++ • Reference Variables • Reference Variables • Student joe (“Geigel” , “Joe”, “GCCIS”, “CS”); – Alias for an already existing object • Student &fred = joe; – Usually used to pass function arguments by reference. – Cannot change what they point to joe Joe Geigel fred Variables in C++ Variables in C++ -- Examples Student joe (“Geigel” , “Joe”, “GCCIS”, “CS”); • Reference variable Student *joe_ptr (new Student (“Schmoe” , “Joe”, “GCCIS”, “CS”); – Accessing class members Student &joe_ref (joe); • Uses the . Syntax // okay joe = *joe_ptr; • Student joe (“Geigel” , “Joe”, “GCCIS”, “CS”); *joe_ptr = joe; • joe.getGrades(); joe_ref = *joe_ptr; // changes joe • Student &fred (joe); joe = joe_ref; • fred.getGrades(); // dangerous joe_ptr = &joe; joe_ptr = &joe_ref; Variables in C++ static • static class members like in Java: • Questions? – the member has no knowledge of any particular instance of the class – data member: there is only one copy shared by all – member function: cannot access non-static data or functions

static static • In header file: • In source file class Tribble { void Tribble::report() public: { ... } Tribble(); unsigned long Tribble::count = 0; ~Tribble(); public: static void report(); static unsigned long count; }; static static • Local variables can also be declared as • Questions? static . void foo () { static int a = 0; … a = a + 1; } Functions Functions • Declaration vs definitions • void and void * – Declaration is the function signature – void – indicates that a function does not return • Required before function can be used a value • Often included in a header file • Can exist in multiple files – void * -- function returns a “generic” pointer • Must be typecast to correct pointer type • char *strcpy (char * to, char* from); • Use with caution – Definition • Actual code • Must defined once and only once

Functions Functions – Pass by value • In C++ function arguments are pass by • Get around this by changing the variable value: type of the arguments void foo (aClass a) void foo (aClass *a) aClass i(7); aClass i(7); { { foo (i); foo (&i); a.moo = 12; a->moo = 12; } } Functions – Pass by value const • Any variable declared as const cannot be • Cleaner means is to use reference variables: changed – Like final in Java. void foo (aClass &a) aClass i(7); – If the variable is a pointer then the object / data { item pointed to cannot be changed. foo (i); • const aClass *a (new aClass(7)) a.moo = 12; • a->moo = 7; // error } Functions – Pass by value Functions – Pass by value • Yet another variable type: • Works for function arguments as well. – Constant pointers • Once defined, the data/object pointed to by the pointer cannot be changed. void foo (const aClass *a) aClass i(7); { foo (&i); • const aClass *a (new aClass(7)) a->moo = 12; // error • a->moo = 7; // error }

Functions – Pass by value const • A class method can also be declared as • Furthermore const – This means that the method will not change the object. void foo (aClass *a) const aClass *i (new aClass(7)); { class aClass { a->moo = 13; public printValues () const; foo (i); // error } public changeValues(); } const Functions • Const methods • Question? void foo (const aClass *a) { a->printValues(); // okay a->changeValues(); // error }