Duhok Polytechnic University Amedi Technical Institute/ IT Dept. Halkawt Rajab Hussain

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1 Duhok Polytechnic University Amedi Technical Institute/ IT Dept. By Halkawt Rajab Hussain

2 Pointers: Pointer declaration and initialization. Pointer To Pointer. Arithmetic operation on pointer variable. Pointer and array. 11/16/2016 1

3 Pointers: A pointer is a variable whose value is the address of another variable i.e., the direct address of the memory location. similar to any variable or constant, you must declare a pointer before you can use it to store any variable address. C# allows using pointer variables in a function of code block when it is marked by the unsafe modifier. The unsafe code or the unmanaged code is a code block that uses a pointer variable. The general form of a pointer declaration is. type *var-name; 11/16/2016 2

Compiling Unsafe Code: For compiling unsafe code, you have to

If you are using Visual Studio IDE then you need to enable use of

To do this: Open project properties by double clicking the

4 Compiling Unsafe Code: For compiling unsafe code, you have to specify the /unsafe command-line switch with command-line compiler. If you are using Visual Studio IDE then you need to enable use of unsafe code in the project properties. To do this: Open project properties by double clicking the properties node in the Solution Explorer. Click on the Build tab. Select the option "Allow unsafe code". 11/16/2016 3

5 Following are valid pointer declarations: int *ip; /* pointer to an integer */ double *dp; /* pointer to a double */ float *fp; /* pointer to a float */ char *ch /* pointer to a character */ Operator Meaning: & The address-of operator returns a pointer to the address of a value. * The dereference operator returns the value at the address of a pointer. -> The member access operator is used to access the members of a type via a pointer. 11/16/2016 4

6 Pointer Initialization: To obtain the address of a unary expression, which evaluates to a fixed variable, use the address-of operator: int number; int* p = &number; //address-of operator & Assign the address of number to a pointer: int* p = &number; Initialization of number. *p = 100; Print the value of *p: Console.WriteLine("Value at the location pointed to by p: 0:", *p); 11/16/2016 5

7 Pointer Initialization: Passing Pointers as Parameters to Methods. You can pass a pointer variable to a method as parameter. The following example illustrates this: using System; namespace UnsafeCodeApplication class TestPointer public unsafe void swap(int* p, int *q) int temp = *p; *p = *q; *q = temp; public unsafe static void Main() TestPointer p = new TestPointer(); int var1 = 10; int var2 = 20; int* x = &var1; int* y = &var2; Console.WriteLine("Before Swap: var1:0, var2: 1", var1, var2); p.swap(x, y); Console.WriteLine("After Swap: var1:0, var2: 1", var1, var2); Console.ReadKey(); 11/16/2016 6

8 Pointer Initialization: Print the address stored in p: Console.WriteLine("The address stored in p: 0", (int)p); Example / without pointer. using system; namespace math class compute static int square(int num) return num*num; static void Main(String[] args) Console.WriteLine(square(5)); Example / using pointer. using system; namespace math class compute static unsafe int square(int* num) return *num=*num * *num; static void Main(String[] args) int num=5; unsafe Console.WriteLine(square(&num)); 11/16/2016 7

9 Pointer To Pointer: int x=5; int* p=&x; Int** pp=&p; *p x **pp Console.WritLine( OutPut: +*p); Console.WritLine( OutPut: +**p); OutPut: 5 OutPut: 5 Console.WriteLine( OutPut: + (int)p); Console.WriteLine( OutPut: + (int)*pp); Console.WriteLine( OutPut: + (int)&x); OutPut:? OutPut:? OutPut:? 11/16/2016 8

10 Arithmetic operation on pointer variable: You can perform arithmetic operations on the pointers similar to any variable. However, performing arithmetic operations on pointers is different from performing those on the other variables. 11/16/2016 9

11 Example In this example, you step through an array by incrementing the pointer by the size of int. With each step, you display the address and the content of the array element. class IncrDecr unsafe static void Main(String[] args) int[] numbers = 0,1,2,3,4; // Assign the array address to the pointer: fixed (int* p1 = numbers) // Step through the array elements: for(int* p2=p1; p2<p1+numbers.length; p2++) Address:1", *p2, (long)p2); 11/16/

12 Examples about arithmetic operations using System; class Test static void Main() unsafe int* values = stackalloc int[20]; int* p = &values[1]; int* q = &values[15]; Console.WriteLine("p - q = 0", p - q); Console.WriteLine("q - p = 0", q - p); int x = 10; int y = 20; int* px = &x; *px = 30; px = &y; Console.WriteLine((int)&y); Console.WriteLine((int)px); Console.WriteLine((int)++px); int* arr = stackalloc int[4]; int* p = arr; for (int i = 0; i < 4; ++i) arr[i] = i; for (int i = 0; i < 4; ++i) Console.WriteLine((int)p); Console.WriteLine(*p); ++p; 11/16/

Pointer and Array: In C#, an array name and a pointer to a data type same as the array data, are not the same variable type. For example, int *p and int[] p, are not same type.

13 Pointer and Array: In C#, an array name and a pointer to a data type same as the array data, are not the same variable type. For example, int *p and int[] p, are not same type. You can increment the pointer variable p because it is not fixed in memory but an array address is fixed in memory, and you can't increment that. Therefore, if you need to access an array data using a pointer variable, you need to fix the pointer using the fixed keyword. 11/16/

14 Pointer and Array: Example static void Main(string[] args) char[] arr = 'a', 'b','c'; unsafe p=p+i p =p+i p =p+i a b c fixed ( char* p = arr) for (int i = 0; i < 3; i++) Console.WriteLine("Address of list[0]=1", i, (int)(p + i)); Console.WriteLine("Value of list[0]=1", i, *(p + i)); 11/16/

15 Example/Write a swap function without temp variable using Exclusive or? using system; namespace swapping; class Exchange static unsafe void swap( int *x, int* y) *x = *x ^ *y; *y = *y ^ *x; *x = *x ^ *y; static void Main(String[] args) int a=10; int b=20; unsafe swap(&a,&b); Console.WriteLine( a= +a); Console.WriteLine( b= +b); 11/16/

16 Thanks Any Questions 11/16/

Duhok Polytechnic University Amedi Technical Institute/ IT Dept. Halkawt Rajab Hussain

Duhok Polytechnic University Amedi Technical Institute/ IT Dept. By Halkawt Rajab Hussain 2016-04-02 Inheritance: Concept of Inheritance. Types of inheritance. Virtual base class method. Interface. 4/1/2017