C/Data Structure Algorithm/Link List
illustrates the use and maintenance of doubly linked lists
<source lang="cpp"> /* C: The Complete Reference, 4th Ed. (Paperback) by Herbert Schildt ISBN: 0072121246 Publisher: McGraw-Hill Osborne Media; 4 edition (April 26, 2000)
- /
/* A simple mailing list program that illustrates the
use and maintenance of doubly linked lists.
- /
- include <stdio.h>
- include <stdlib.h>
- include <string.h>
struct address {
char name[30]; char street[40]; char city[20]; char state[3]; char zip[11]; struct address *next; /* pointer to next entry */ struct address *prior; /* pointer to previous record */
}; struct address *start; /* pointer to first entry in list */ struct address *last; /* pointer to last entry */ struct address *find(char *); void enter(void), search(void), save(void); void load(void), list(void); void mldelete(struct address **, struct address **); void dls_store(struct address *i, struct address **start,
struct address **last);
void inputs(char *, char *, int), display(struct address *); int menu_select(void); int main(void) {
start = last = NULL; /* initialize start and end pointers */
for(;;) {
switch(menu_select()) {
case 1: enter(); /* enter an address */
break;
case 2: mldelete(&start, &last); /* remove an address */
break;
case 3: list(); /* display the list */
break;
case 4: search(); /* find an address */
break;
case 5: save(); /* save list to disk */
break;
case 6: load(); /* read from disk */
break;
case 7: exit(0);
}
}
return 0;
} /* Select an operation. */ int menu_select(void) {
char s[80];
int c;
printf("1. Enter a name\n");
printf("2. Delete a name\n");
printf("3. List the file\n");
printf("4. Search\n");
printf("5. Save the file\n");
printf("6. Load the file\n");
printf("7. Quit\n");
do {
printf("\nEnter your choice: ");
gets(s);
c = atoi(s);
} while(c<0 || c>7);
return c;
} /* Enter names and addresses. */ void enter(void) {
struct address *info;
for(;;) {
info = (struct address *)malloc(sizeof(struct address));
if(!info) {
printf("\nout of memory");
return;
}
inputs("Enter name: ", info->name, 30);
if(!info->name[0]) break; /* stop entering */
inputs("Enter street: ", info->street, 40);
inputs("Enter city: ", info->city, 20);
inputs("Enter state: ", info->state, 3);
inputs("Enter zip: ", info->zip, 10);
dls_store(info, &start, &last);
} /* entry loop */
} /* This function will input a string up to
the length in count and will prevent the string from being overrun. It will also display a prompting message. */
void inputs(char *prompt, char *s, int count) {
char p[255];
do {
printf(prompt);
fgets(p, 254, stdin);
if(strlen(p) > count) printf("\nToo Long\n");
} while(strlen(p) > count);
p[strlen(p)-1] = 0; /* remove newline character */
strcpy(s, p);
} /* Create a doubly linked list in sorted order. */ void dls_store(
struct address *i, /* new element */ struct address **start, /* first element in list */ struct address **last /* last element in list */
) {
struct address *old, *p;
if(*last==NULL) { /* first element in list */
i->next = NULL;
i->prior = NULL;
*last = i;
*start = i;
return;
}
p = *start; /* start at top of list */
old = NULL;
while(p) {
if(strcmp(p->name, i->name)<0){
old = p;
p = p->next;
}
else {
if(p->prior) {
p->prior->next = i;
i->next = p;
i->prior = p->prior;
p->prior = i;
return;
}
i->next = p; /* new first element */
i->prior = NULL;
p->prior = i;
*start = i;
return;
}
}
old->next = i; /* put on end */
i->next = NULL;
i->prior = old;
*last = i;
} /* Remove an element from the list. */ void mldelete(struct address **start, struct address **last) {
struct address *info;
char s[80];
inputs("Enter name: ", s, 30);
info = find(s);
if(info) {
if(*start==info) {
*start=info->next;
if(*start) (*start)->prior = NULL;
else *last = NULL;
}
else {
info->prior->next = info->next;
if(info!=*last)
info->next->prior = info->prior;
else
*last = info->prior;
}
free(info); /* return memory to system */
}
} /* Find an address. */ struct address *find( char *name) {
struct address *info;
info = start;
while(info) {
if(!strcmp(name, info->name)) return info;
info = info->next; /* get next address */
}
printf("Name not found.\n");
return NULL; /* not found */
} /* Display the entire list. */ void list(void) {
struct address *info;
info = start;
while(info) {
display(info);
info = info->next; /* get next address */
}
printf("\n\n");
} /* This function actually prints the fields in each address. */ void display(struct address *info) {
printf("%s\n", info->name);
printf("%s\n", info->street);
printf("%s\n", info->city);
printf("%s\n", info->state);
printf("%s\n", info->zip);
printf("\n\n");
} /* Look for a name in the list. */ void search(void) {
char name[40];
struct address *info;
printf("Enter name to find: ");
gets(name);
info = find(name);
if(!info) printf("Not Found\n");
else display(info);
} /* Save the file to disk. */ void save(void) {
struct address *info;
FILE *fp;
fp = fopen("mlist", "wb");
if(!fp) {
printf("Cannot open file.\n");
exit(1);
}
printf("\nSaving File\n");
info = start;
while(info) {
fwrite(info, sizeof(struct address), 1, fp);
info = info->next; /* get next address */
}
fclose(fp);
} /* Load the address file. */ void load() {
struct address *info;
FILE *fp;
fp = fopen("mlist", "rb");
if(!fp) {
printf("Cannot open file.\n");
exit(1);
}
/* free any previously allocated memory */
while(start) {
info = start->next;
free(info);
start = info;
}
/* reset top and bottom pointers */
start = last = NULL;
printf("\nLoading File\n");
while(!feof(fp)) {
info = (struct address *) malloc(sizeof(struct address));
if(!info) {
printf("Out of Memory");
return;
}
if(1 != fread(info, sizeof(struct address), 1, fp)) break;
dls_store(info, &start, &last);
}
fclose(fp);
}
</source>
