1. Dynamic memory allocation in C and C++
程式設計
潘仁義
CCU COMM

2. Pointers
void main () { int num = 3; int *nump = # …..

3. Dynamic memory allocation in C (1/3)
void some_function () { int *nump; char *letp; planet_t *planetp; …

4. Dynamic memory allocation in C (2/3)
void some_function () { int *nump; char *letp; planet_t *planetp; …
#include <stdlib.h>
nump=(int*) malloc(sizeof(int)); letp = (char*) malloc(sizeof(char)); planetp = (planet_t *) malloc(sizeof(planet_t));

5. Dynamic memory allocation in C (3/3)
void some_function () { int *nump; char *letp; planet_t *planetp; …
nump=(int*) malloc(sizeof(int)); letp = (char*) malloc(sizeof(char)); planetp = (planet_t *) malloc(sizeof(planet_t));
*nump = 307; *letp = ‘Q’; *planetp = blank_planet;

6. Allocation of Arrays with calloc

7. Allocation of Arrays with calloc (cont’d)

8. Returning cells to the Heap
… free(letp); free(nump); free(planetp); … free(string1); free(array_of_nums); free(array_of_planets);
double *xp, *xcopyp; xp =(double *)malloc(sizeof(double)); *xp = 49.5; xcopyp = xp; free(xp);
『*xcopyp』should not be used after it freed or errors can result

9. Dynamic memory allocation in C++
int *nump; char *letp; planet_t *planetp; char *string1; int *array_of_nums; planet_t *array_of_planets;
nump= new int; letp = new char; planetp = new planet_t; string1 = new char[str_size]; array_of_nums = new int[num_nums]; array_of_planets = new planet_t[num_planets];
delete nump; delete letp; delete planetp; delete [ ] string1; delete [ ] array_of_nums; delete [ ] array_of_planets;

10. Linked list Children’s Pop Beads in a Chain

11. Linked list Structures with pointer components
typedef struct node_s { char current[3]; int volts; struct node_s *linkp; } node_t;
node_t *n1_p, *n2_p, *n3_p; n1_p = (node_t *)malloc(sizeof(node_t)); n1_p->volts = 115; n2_p = (node_t *)malloc(sizeof(node_t)); n2_p->volts = 12; n3_p = n2_p; /* 令n3_p指向n2_p所指的地方 */

12. 可用 n2_p->volts n3_p->volts 或 n1_p->linkp->volts
Linking Two Nodes
n1_p->linkp = n2_p; /* 令上面的linkp 指向下面 */
可用 n2_p->volts n3_p->volts 或 n1_p->linkp->volts

13. Three-Node Linked List
n2_p->linkp = (node_t *) malloc(sizeof(node_t)); n2_p->linkp->volts=220; strcpy(n2_p->linkp->current, “AC”);
n2_p->linkp->linkp = NULL;

14. Linked list operations
After an Insertion
After a Deletion

15. Common programming error
var->component
is valid only if var is of a pointer-to-structure
The most common error is
an attempt to follow a NULL pointer
Checking before access
Do not attempt to reference a node after freeing it