Teach Yourself Borland C++ in 14 Days - portal

80 Day 3
TIP
Remember that a function can return only one value. By passing
parameters by reference you can achieve the effect of a function
returning more than one value. The function still only returns one
value, but the objects passed by reference are updated, so the function
effectively returns multiple values.
As I said, the other reason to pass parameters by reference is to eliminate the overhead of
making a copy of the object each time the function is called. When dealing with primitive
data types, there is no real overhead involved in making a copy. When dealing with structures
and classes, however, the overhead is something to be considered. You should pass structures
of any consequence by reference, as the following code demonstrates:
// structure passed by reference
void someFunction(MyStructure& s)
{
// do some stuff with ‘s’
return;
}
MyStructure myStruct;
// do some stuff, then later...
someFunction(myStruct);
Notice that the function call looks exactly the same whether the object is being passed by
reference or by value.
Do you see a potential problem with passing by reference? If you pass by reference, you avoid
the overhead of making a copy of the object, but now the object can be modified by the
function. Sometimes you don’t want the object to be modified by the function. So what if you
want to pass by reference but make sure the object is not modified? Read on and I’ll tell you.
The const Keyword
NEW TERM
The const keyword will allow you to declare a variable as constant.
Once a variable is declared with const, it cannot be changed. The solution, then, is to pass
by reference and make the object const:
void someFunction(const MyStruct& s)
{
// do some stuff with ‘s’
return;
}
MyStructure myStruct;
// later
someFunction(myStruct);