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CS 192

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.

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CS 192

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

  2. 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

  3. 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

  4. Initializing Multi-Dimentional Arrays static int example[5][3] = { 1, 2, 3, 4, 5, 6, 7 }; 1 2 3 4 5 6 7 0 0 0 0 0 0 0 0 static int example[5][3] = { { 1, 2, 3 }, { 4 }, { 5, 6, 7 } }; 1 2 3 4 0 0 5 6 7 0 0 0 0 0 0

  5. 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

  6. 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

  7. 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; }

  8. Array of Strings vs. Array of Pointers • 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 • 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”};

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

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

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

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

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

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

  15. 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;

  16. 0 1 2 3 4 5 iarray 0 1 2 3 Array of Pointers A two dimensional array of RSIZE*CSIZE 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); } }

  17. 300 200 100 20 ippp ipp ip a 400 300 200 100 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; 20 100 20 200 100 20 300 200 100 20

  18. Dynamic Array of Pointers A two dimensional array of RSIZE*CSIZE 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); } } matrix 0 1 2 3 4 5 0 1 2 3

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