CS 192 Lecture 13 Winter 2003 January 5-6, 2004 Dr. Shafay Shamail

Void Pointer int age = 20; int *ageptr = &age; void *vptr = (void *)ageptr; int *newptr = (int *)vptr; Can’t do: vptr++ vptr— vptr + 2 As the base type of vptr is not known

Pointers and Multidimensional Arrays int ar[2][3] = { { 0, 1, 2 }, { 3, 4, 5 } }; ar[1][2]= *(ar[1] + 2) = *(*(ar+1) + 2) = *(int *)((char *)ar + (1*3*4) + (2*4)) = *(int *)((char *)ar + 20) Where 3 = # of elements in each row And each int is of 4 byte long

Initializing Multi-Dimentional Arrays static int example[5][3] = { { 1, 2, 3 }, { 4 }, { 5, 6, 7 } }; static int example[5][3] = { 1, 2, 3, 4, 5, 6, 7 };

Initializing Multi-Dimensional Arrays static int example[][3][2] = { { {1, 1}, {2, 2}, {3,3} }, { {4, 4}, {5, 5}, {6,6} }, { {1, 1}, {2, 2}, {3,3} }, { {4, 4}, {5, 5}, {6,6} } }; 4-by-3-by-2 array

Arrays of Pointers char *fortunes[] = { "Soon, you will come into some money.\n", "A new love will enter your life.\n", "You will live long and prosper.\n", "Now is a good time to invest for the future.\n", "A close friend will ask for a favor.\n" }; cout << fortunes[1] << endl << fortunes<<endl << *(fortunes) << endl << *(fortunes[2]) << endl; Output: A new love will enter your life 0012FFC6 Soon, you will come into some money Y

Arrays of Pointers … Two dimensional string pointers e.g. C++ dictionary char *keyword[][2] = { "for", "for(initialization; condition; increment)", "if", "if(condition)... else...", "switch", "switch(value) { case-list }", "while", "while(condition)...", // add the rest of the C++ keywords here "", "" // terminate the list with nulls }; int main() { char str[80]; int i; cout << "Enter keyword: "; cin >> str; for(i=0; *keyword[i][0]; i++) if(!strcmp(keyword[i][0], str)) cout << keyword[i][1]; return 0; }

Array of Strings vs. Array of Pointers  char movies[5][20] = {“Godfather”, “Maula Jatt”, “A Fish Called Wanda”, “Blade Runner”, “Spiderman”};  char *movies[5] = {“Godfather”, “Maula Jatt”, “A Fish Called Wanda”, “Blade Runner”, “Spiderman”}; each column is 20 characters wide due to the longest movie name wasted space the strings are placed contiguously in memory without wasting space pointers in the array movie point to them

The new operator int *x_ptr = new int; OR int *xptr; xptr = new int; //heap Dynamic Allocation

int *xptr=new int; *xptr = 73; int *x2ptr = new int; *x2ptr = 65; Dynamic Allocation

What is wrong here? int *xptr = new int; *xptr = 73; int *x2ptr; *x2ptr=65; Dynamic Allocation

int *xptr = new int; *xptr = 73; int *x2ptr; x2ptr = xptr; *x2ptr = 65; Dynamic Allocation

//What is wrong here? int *xptr = new int; *xptr = 73; int *x2ptr = new int; x2ptr = xptr; *x2ptr = 65; //memory leak Dynamic Allocation

int *myptr = new int(73); cout << *myptr; delete myptr; Dynamic Allocation

const int SIZE = 10; double *ptr = new double[SIZE]; /*10 element array*/ int i; for (i=0; i<SIZE; i++) { ptr[i] = 2.0*i; } for (i=0; i<SIZE; i++) { cout << ptr[i] << endl; } delete []ptr; Dynamic Allocation

Array of Pointers const int RSIZE = 4; const int CSIZE = 6; int * iarray[RSIZE]; for(int k=0; k<RSIZE; k++) { iarray[k] = new int [CSIZE]; if (iarray[k] == NULL) { cerr << “Memory Allocation Error…\n”; cerr << “Exiting …\n”; exit(-1); } A two dimensional array of RSIZE*CSIZE iarray

Double and Tripple Pointers int a = 20; int *ip = &a; int **ipp = &ip; int ***ippp = &ipp; cout << a << endl; cout << ip << *ip << endl; cout << ipp << *ipp << **ipp << endl; cout << ippp << *ippp << **ippp << ***ippp << endl; 20 a 100 ip 200 ipp 300 ippp

Dynamic Array of Pointers const int RSIZE = 4; const int CSIZE = 6; int ** matrix; matrix = new int * [RSIZE]; for(int k=0; k<RSIZE; k++) { matrix[k] = new int [CSIZE]; if (matrix[k] == NULL) { cerr << “Memory Allocation Error…\n”; cerr << “Exiting …\n”; exit(-1); } A two dimensional array of RSIZE*CSIZE matrix