Teach Yourself Borland C++ in 14 Days - portal

NOTE
Up to Your Neck in C++
Now you are free to pass by reference and not worry that your object might be modified by
the function. Note that the function call itself stays the same and that only the function
definition (and declaration) is modified with the const keyword.
If you attempt to modify a const object, you will get a compiler error
stating, Cannot modify a const object. The following code will
generate that error message:
void someFunction(const MyStruct& s)
{
s.dataMember = 100; // cannot modify a const object
return;
}
Once you declare an object as const, the compiler will make sure you
don’t modify the object.
Note that the object is const only within the function. The object can be modified both
before and after the function returns (provided it was not initially declared as const).
Passing by pointer is essentially the same as passing by reference. Passing by pointer has a
couple of syntactical headaches that make it less desirable than passing by reference. Let’s take
the IncrementPosition() function from the first example in this section and modify it to pass
by pointer rather than by reference:
void IncrementPosition(int* xPos, int* yPos)
{
*xPos++; // dereference, then increment
*yPos++;
}
Note that the pointer has to be dereferenced before it can be incremented. Most of the time
your needs will be best served by passing by reference, but you may pass by pointer if a
situation dictates the need. When passing char arrays, you will usually pass by pointer rather
than by reference because you can use a pointer to a char array and the name of the array
interchangeably. When passing character arrays, it is better to pass by pointer.
The new and delete Operators
Up to this point I have been talking primarily about aspects of the C++ language that come
from C. From this point on we’ll be looking at features that are specific to the C++ language.
The new and delete operators are two important C++ language features.
81
3