![Array Name is a pointer constant
#include <iostream>
using namespace std;
void main (){
int a[5];
cout << "Address of a[0]: " << &a[0] << endl
<< "Name as pointer: " << a << endl;
}
Result:
Address of a[0]: 0x0065FDE4
Name as pointer: 0x0065FDE4](https://image.slidesharecdn.com/pointers1-190927162726/85/Pointers-13-320.jpg)
![Dereferencing An Array Name
#include <iostream>
using namespace std;
void main(){
int a[5] = {2,4,6,8,22};
cout << *a << " "
<< a[0];
} //main
2
4
8
6
22a[4]
a[0]
a[2]
a[1]
a[3]](https://image.slidesharecdn.com/pointers1-190927162726/85/Pointers-14-320.jpg)
![*(a+n) is identical to a[n]
Dereferencing Array Pointers
2
4
8
6
22
a
a + 2
a + 4
a + 3
a + 1
a[3] or *(a + 3)
a[2] or *(a + 2)
a[1] or *(a + 1)
a[0] or *(a + 0)
a[4] or *(a + 4)](https://image.slidesharecdn.com/pointers1-190927162726/85/Pointers-16-320.jpg)
![Array of Pointers & Pointers to Array
a
b
c
An array of Pointers
p
int a = 1, b = 2, c = 3;
int *p[5];
p[0] = &a;
p[1] = &b;
p[2] = &c;
int list[5] = {9, 8, 7, 6, 5};
int *p;
P = list;//points to 1st entry
P = &list[0];//points to 1st entry
P = &list[1];//points to 2nd entry
P = list + 1; //points to 2nd entry
A pointer to an array](https://image.slidesharecdn.com/pointers1-190927162726/85/Pointers-17-320.jpg)
Pointers
- 2. Pointers A pointer is a variable used to store the address of a memory cell. We can use the pointer to reference this memory cell 100… … 1024 … Memory address: 1024 1032 … 1020 integer pointer
- 3. Pointer Types Pointer C++ has pointer types for each type of object ○ Pointers to int objects ○ Pointers to char objects ○ Pointers to user-defined objects (e.g., RationalNumber) Even pointers to pointers ○ Pointers to pointers to int objects
- 4. Pointer Variable Declaration of Pointer variables type* pointer_name; //or type *pointer_name; where type is the type of data pointed to (e.g. int, char, double) Examples: int *n; RationalNumber *r; int **p; // pointer to pointer
- 5. Address Operator & The "address of " operator (&) gives the memory address of the variable Usage: &variable_name 100… … … … Memory address: 1024 int a = 100; //get the value, cout << a; //prints 100 //get the memory address cout << &a; //prints 1024 … 1020 a
- 6. Address Operator & 10088 … … … Memory address: 1024 1032 a … 1020 b #include <iostream> using namespace std; void main(){ int a, b; a = 88; b = 100; cout << "The address of a is: " << &a << endl; cout << "The address of b is: " << &b << endl; } Result is: The address of a is: 1020 The address of b is: 1024
- 7. Pointer Variables The value of pointer p is the address of variable a A pointer is also a variable, so it has its own memory address 10088 … 1024 … Memory address: 1024 1032 … 1020 a p int a = 100; int *p = &a; cout << a << " " << &a <<endl; cout << p << " " << &p <<endl; Result is: 100 1024 1024 1032
- 9. Dereferencing Operator * We can access to the value stored in the variable pointed to by using the dereferencing operator (*), 10088 … 1024 … Memory address: 1024 1032 … 1020 int a = 100; int *p = &a; cout << a << endl; cout << &a << endl; cout << p << " " << *p << endl; cout << &p << endl; Result is: 100 1024 1024 100 1032 a p
- 10. Another Pointer Example int a = 3; char s = ‘z’; double d = 1.03; int *pa = &a; char *ps = &s; double *pd = &d; % sizeof returns the # of bytes… cout << sizeof(pa) << sizeof(*pa) << sizeof(&pa) << endl; cout << sizeof(ps) << sizeof(*ps) << sizeof(&ps) << endl; cout << sizeof(pd) << sizeof(*pd) << sizeof(&pd) << endl;
- 11. Reference Variables A reference variable serves as an alternative name for an object int m = 10; int &j = m; // j is a reference variable cout << “value of m = “ << m << endl; //print 10 j = 18; cout << “value of m = “ << m << endl; // print 18
- 12. Pointers and Arrays The name of an array points only to the first element not the whole array. 1000 1012 1016 1004 1008
- 13. Array Name is a pointer constant #include <iostream> using namespace std; void main (){ int a[5]; cout << "Address of a[0]: " << &a[0] << endl << "Name as pointer: " << a << endl; } Result: Address of a[0]: 0x0065FDE4 Name as pointer: 0x0065FDE4
- 14. Dereferencing An Array Name #include <iostream> using namespace std; void main(){ int a[5] = {2,4,6,8,22}; cout << *a << " " << a[0]; } //main 2 4 8 6 22a[4] a[0] a[2] a[1] a[3]
- 15. Pointer Arithmetic Given a pointer p, p+n refers to the element that is offset from p by n positions. 2 4 8 6 22 a a + 2 a + 4 a + 3 a + 1 p p + 2 p + 3 p - 1 p + 1
- 16. *(a+n) is identical to a[n] Dereferencing Array Pointers 2 4 8 6 22 a a + 2 a + 4 a + 3 a + 1 a[3] or *(a + 3) a[2] or *(a + 2) a[1] or *(a + 1) a[0] or *(a + 0) a[4] or *(a + 4)
- 17. Array of Pointers & Pointers to Array a b c An array of Pointers p int a = 1, b = 2, c = 3; int *p[5]; p[0] = &a; p[1] = &b; p[2] = &c; int list[5] = {9, 8, 7, 6, 5}; int *p; P = list;//points to 1st entry P = &list[0];//points to 1st entry P = &list[1];//points to 2nd entry P = list + 1; //points to 2nd entry A pointer to an array
- 18. NULL pointer NULL is a special value that indicates an empty pointer If you try to access a NULL pointer, you will get an error int *p; p = 0; cout << p << endl; //prints 0 cout << &p << endl;//prints address of p cout << *p << endl;//Error!