CPP Understanding Pointers

What is a C++ Pointer?

  • Each variable in a C++ program has an byte address in the RAM and occupies a number of bytes depending on the type of the variable.
  • Usually, as a programmer, you don't need to know the particular address of any given variable because the compiler handles the details.

Using address-of operator

  • If you want this information, though, you can use the address-of operator (&), which returns the address of an object in memory.
    Examples of address-of operator (&):
    Source code Result
    #include <iostream>
    using namespace std;
    int main() {
        int rats = 101;
        cout << "rats = " << rats << "\n";
        cout << "rats address = " << &rats << "\n";
        return 0;
    }
    rats = 101
    rats address = 001EFC4C

    You can download this example here (needed tools can be found in the right menu on this page).

  • You can store a Variable's Address in a Pointer.
    int * pRats = 0; // pRats is a pointer to integer
  • This declares pRats to be a pointer to an int. That is, pRats is declared to hold the address of an integer.
  • Many programmers follow the convention of naming all pointers with an initial p, as in pRats, pAge or pNumber
    unsigned short int oldNumber = 50;       // make a variable
    unsigned short int * pNumber = &oldNumber;  // make a pointer to oldNumber
    
  • pNumber is a pointer that now contains the address of the oldNumber variable

Using the asterisk (*)

  • The asterisk (*) is used in two distinct ways with pointers:
    1. as part of a pointer declaration
    2. and also as a dereference operator.
    unsigned short int oldNumber = 50;       // make a variable
    // The next is a pointer declaration which you read as "int *" 
    // You must read asterisk (*) as related to the type (int) 
    unsigned short int * pNumber = &oldNumber;  // make pointer to oldNumber
    unsigned short int myNumber;
    // The next two statements uses dereference operator 
    // You must now read The asterisk (*) as related to the pointer variable
    // The return value is the value of what the pointer points to 
    myNumber = * pNumber;
    // which also can be changed       
    *pAge=45;
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