Review-pointer, second-level pointer, linked list, review pointer

Review-pointer, second-level pointer, linked list, review pointer

Level 1 pointer

• Int * p; // defines an int type (4 bytes) pointer p
• & P // represents the address location of p.
• P // indicates the address location pointed to by p (that is, the value of the p variable)
• * P // indicates the content in the address pointed to by p

 

So *'s role:The value of the p variable acts as the address to access the content of this address.

 

Level 2 pointer

• Int ** pp // defines an int * pointer pp
• & Pp // address location of the pp
• Pp // indicates the address pointed to by pp, for example, pp = & p. Note that pp is of the int Type X. Therefore, an error will be reported if pp is directed to another type of address,
• * Pp // indicates the content on the address pointed to by pp. For example, if pp = & p, * pp will access the content of & p.
• ** Pp // indicates that the content on the address pointed by pp is used as the address to access the content of this address. * pp = * (* pp) = * p

For example:

Int main () {int I = 5; // suppose & I = 0x100 int * p = & I; // assume & p = 0x500 int ** pp = & p; // assume & pp = 0x1000/* So & I = 0x100, I = 5 & p = 0x500 p = 0x100 * p = 5 & pp = 0x1000 pp = 0x500 * pp = 0x100 ** pp = 5 */}

 

 

Linked List

First, let's talk about malloc and free:

This function is required when you add or release a linked list to prevent content from being automatically released.

void *malloc(int size);

 

The return value of malloc is of the void * type. Therefore, you must use a pointer to obtain the value and use a forced conversion function.

void free(void *ptr);

 

Release address, used with malloc, for example:

Char * p; char str [] = "ABCD"; p = (char *) malloc (strlen (str); // the pointer must be used for obtaining, and forcibly convert strcpy (p, str );...... free (p );

 

 

An example of a two-way linked list is as follows: 

# Include "stdio. h "
# include <stdlib. h> 
# include "string. h "
typedef struct NAME {
char * name; 
struct NAME * preced; 
// the previous name linked list member struct NAME * next; 
// The member of the next name linked list
} 
T_NAME, * PT_NAME; 
PT_NAME g_ptNameListHead = NULL; 
// void add_LinkList (PT_NAME nameNew) {
PT_NAME ptTamp; 
int I = 0;
If (g_ptNameListHead = NULL)
 // Add the linked list {
g_ptNameListHead = nameNew;
 return;
} else {
ptTamp = g_ptNameListHead; 
while (ptTamp-> next) 
for the first time) 
// whether the members of the next linked list are empty {ptTamp = ptTamp-> next;} ptTamp-> next = nameNew; 
// Add the members of the next linked list nameNew-> preced = ptTamp; // Add the return;
} 
void add_name (char str []) {
PT_NAME ptTamp;
 char * p; 
p = (char *) to the next linked list Member *) 
malloc (strlen (str); 
strcpy (p, str); 
ptTamp = (PT_NAME) malloc (sizeof (T_NAME);
 ptTamp-> name = p; 
ptTamp-> preced = NULL; 
ptTamp-> next = NULL; 
add_LinkList (ptTamp ); 
// Add a linked list}/* locate the name Position */
PT_NAME find_name (char str []) {
PT_NAME ptTamp;
 if (g_ptNameListHead = NULL) 
return NULL;
PtTamp = g_ptNameListHead; 
while (ptTamp) {
if (strcmp (ptTamp-> name, str) = 0) 
// find {
return ptTamp ;
}
 else 
ptTamp = ptTamp-> next;
} return 
NULL;} 
int del_name (char str []) {
PT_NAME ptTamp;
 PT_NAME ptLast; 
PT_NAME ptNext;
PtTamp = find_name (str); 
if (! PtTamp) return-1; 
if (ptTamp = g_ptNameListHead)
 // if the chain table header is removed {
g_ptNameListHead = ptTamp-> next; 
// point to the next linked list member
} else {
/* Get the previous linked list member and the next linked list member */
ptLast = ptTamp-> preced;
 ptNext = ptTamp-> next; 
/* remove the current linked list member */
ptLast-> next = ptNext;
 ptNext-> preced = ptLast;
} 
free (ptTamp-> name); 
free (ptTamp); 
return 0 ;
} void List_name (void) {
int I = 0;
 PT_NAME ptTamp = g_ptNameListHead; 
while (ptTamp) {
printf ("<% d> % s \ n", I, ptTamp-> name); 
ptTa Mp = ptTamp-> next ;
}
} void scanf_name (char cmd) {
char name [128];
 switch (cmd) {
case 'A ': 
// add {printf ("please enter name: \ n"); 
scanf ("% s", name); 
add_name (name ); 
printf ("add % s OK \ n", name); 
break;} 
case 'D': 
// del {printf ("please enter name: \ n ");
 scanf ("% s", name);
 if (del_name (name) <0) {
printf ("del % s error \ n", name );
}
 else printf ("del % s OK \ n", name); 
break;
} case 'l':
 // list List_name ();
 break;
} Int main (int argc, char ** argv) {
char c;
 while (1) {
printf ("*********************** \ n ");
 printf ("<l> List all the names \ n"); 
printf ("<a> add one name \ n ");
 printf ("<d> del one name \ n");
 printf ("<q> quit \ n "); 
printf ("*********************** \ n"); 
do {
scanf ("% c ", & c);
} while (c! = 'A' & c! = 'D' & c! = 'Q' & c! = 'L');
 switch (c) {
case 'A': 
case 'l': 
case 'D': 
scanf_name (c);
 break;
 case 'q ':
 return 0;
 default: 
break ;}}}