Pointers in Software

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ends, the variables declared in main are not destroyed until the program ends, but the mechanism for handling local variables is the same for main as for any other function) These local variables are sometimes called automatic variables because their dynamic properties are controlled automatically for you They are automatically created when the function in which they are declared is called and automatically destroyed when the function call ends Variables declared outside any function or class de nition, including outside main, are called global variables These global variables are sometimes called statically allocated variables, because they are truly static in contrast to dynamic and automatic variables We discussed global variables brie y in 3 As it turns out, we have no need for global variables and have not used them4
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DEFINE POINTER TYPES
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You can define a pointer type name so that pointer variables can be declared like other variables without the need to place an asterisk in front of each pointer variable For example, the following defines a type called IntPtr, which is the type for pointer variables that contain pointers to int variables:
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typedef int* IntPtr;
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Thus, the following two pointer variable declarations are equivalent:
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IntPtr p;
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int *p;
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You can use typedef to define an alias for any type name or definition For example, the following defines the type name Kilometers to mean the same thing as the type name double:
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typedef double Kilometers;
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typedef
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Once you have given this type definition, you can define a variable of type double as follows:
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Kilometers distance;
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Renaming existing types this way can occasionally be useful However, our main use of typedef will be to define types for pointer variables Keep in mind that a typedef does not produce a new type but is simply an alias for the type definition For example, given the previous definition of Kilometers, a variable of type
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4 Variables declared within a class using the modi er static are static in a different sense than the dynamic/static contrast we are discussing in this section
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Pointers and Dynamic Arrays
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Kilometers may be substituted for a parameter of type double Kilometers and double are two names for the same type
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There are two advantages to using defined pointer type names, such as IntPtr defined previously First, it avoids the mistake of omitting an asterisk Remember, if you intend p1 and p2 to be pointers, then the following is a mistake:
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int *p1, p2;
Since the * was omitted from the p2, the variable p2 is just an ordinary int variable, not a pointer variable If you get confused and place the * on the int, the problem is the same but is more difficult to notice C++ allows you to place the * on the type name, such as int, so that the following is legal:
int* p1, p2;
Although the above is legal, it is misleading It looks like both p1 and p2 are pointer variables, but in fact only p1 is a pointer variable; p2 is an ordinary int variable As far as the C++ compiler is concerned, the * that is attached to the identifier int may as well be attached to the identifier p1 One correct way to declare both p1 and p2 to be pointer variables is
int *p1, *p2;
An easier and less error-prone way to declare both p1 and p2 to be pointer variables is to use the defined type name IntPtr as follows:
IntPtr p1, p2;
The second advantage of using a defined pointer type, such as IntPtr, is seen when you define a function with a call-by-reference parameter for a pointer variable Without the defined pointer type name, you would need to include both an * and an & in the declaration for the function, and the details can get confusing If you use a type name for the pointer type, then a call-by-reference parameter for a pointer type involves no complications You define a call-by-reference parameter for a defined pointer type just like you define any other call-by-reference parameter Here s an example:
void sampleFunction(IntPtr& pointerVariable);