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

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

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

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));

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;

Allocation of Arrays with calloc

Allocation of Arrays with calloc (cont’d)

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

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;

Linked list Children’s Pop Beads in a Chain

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 */

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

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;

Linked list operations After an Insertion After a Deletion

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