Windows Programming Lecture 03. Pointers and Arrays.

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Presentation transcript:

Windows Programming Lecture 03

Pointers and Arrays

Arrays An array is a collection of variables of the same type. Individual array elements are identified by an integer index. In C the index begins at zero and is always written inside square brackets.

According to C language specification, –Single dimensional array name is the starting address of array’s first byte.

–Lower limit of subscript is ZERO whereas Upper limit is n-1. n is size of array

Subscript Operator * () is known as Subscript Operator It has 2 requirements i.e. 1.On left hand side of Subscript Operator there should be a pointer (pointer constant or variable) 2.In between the brackets of Subscript Operator there should be an integer or integral expression whose result is an integer.

Pointer Variable Pointer Constant Due to this statement address of first element will be assigned to ptr.

Behavior of Subscript Operator Using Subscript Operator we can access the elements of array We can do this using pointer variable or pointer constant.

int *ptr, a[5]; 1. ptr = a; // possible 2. a= ptr; // not possible Reason: As per assignment rule on the left side of assignment operator (=) there should be a memory location whose data type should match with RHS value i.e. variable but in line 2 a is a pointer constant not variable so it will give error.

a[2]; OR *(a+2); // 1 write operation ptr[2]; OR *(ptr+2) ; // 1 write operation // 1 read operation

a[2]; *(a+2); Both a and 2 are constants Compiler will directly go to digital address of a i.e. 452 and will add 2 according to the pointer arithmetic Compiler will skip 8 bytes And finally indirection will be performed (i.e.1 write operation)

ptr[2]; *(ptr+2); Ptr is pointer variable and 2 is constant Compiler will access the ptr and will read the address stored in ptr (i.e. 1 read operation) Then it will add 2 according to the pointer arithmetic, and 8 bytes will be skipped. And finally indirection will be performed (i.e.1 write operation)

Multidimensional Arrays in C Multidimensional arrays are simply arrays of arrays (of arrays of arrays...) A multidimensional array like m[3][2] is stored in consecutive memory locations as m[0][0], m[0][1], m[1][0], m[1][1], m[2][0], m[2][1]

Two Dimensional Arrays a[3][5]; a a[0][0] a[0][1]a[0][0]a[0][2] a[1][0] a[2][0] a[0][3]a[0][4]

Two Dimensional Array a[1][4] OR *(a+1)[4] OR *(*(a+1)+4)

Two Dimensional Array Name of two dimensional array is the address of its first row. int a[3][5]; a + 1; // skips 1 row(5 elements)

A complete row will be skipped

Two Dimensional Array Name of two dimensional array is the address of its first row. But after indirection Name of two dimensional array is the address of one element.

Int a [3] [5]; *(*(a+1)+4); a a + 1

Ptr is pointing to a row of 5 integers

int a[2][3][5]; No. of elements= 2*3*5=30 Page 1 Page 2 a

a[1][2][4] Page 1

Two Dimensional Array int a[3][5]; Data type of a is int (*)[5] OR int [5] * int (* ptr)[5]; ptr=a;

Three Dimensional Arrays int a[2][3][5]; Name of three dimensional array is the address of first page in that array.

Three Dimensional Array int a[2][3][5]; Data type of a is int (*)[3][5]; int (* ptr)[3][5]; ptr=a;

Three Dimensional Array a[1][2][3] is equivalent to *(*(*(a+1)+2)+3)

Function Pointer ( ) Function call operator

Operator Precedence C contains many operators, and because of operator precedence, the interactions between multiple operators can become confusing. Operator precedence describes the order in which C evaluates expressions

Operator Precedence ( ) operator has higher precedence then [ ] operator

Function Pointer Function Pointers are pointers, i.e. variables, which point to the address of a function. You must keep in mind, that a running programme gets a certain space in the main-memory. Both, the executable compiled programme code and the used variables, are put inside this memory. Thus a function name in the program code is nothing else than an address.

Function Pointer int *f1(void) Function returning int * int (*f1)(void) Pointer to function returning int.

Function Pointer int **array[ ]; array of pointers to pointers to int. int *( * array)( ); pointer to function returning int *

Questions double b[2][3][4]; ???????? ptr; // data type of ptr ptr=*b; ++ptr; // how many bytes skipped Read the declarations: int ( *systemptr)(int, long *); Char *(*(*a[50]) (void)) (void);