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==scan a file and print out a list of words in ASCII order==

<source lang="cpp">
/*
Practical C Programming, Third Edition
By Steve Oualline
Third Edition August 1997
ISBN: 1-56592-306-5
Publisher: O"Reilly
*/
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
struct node {
struct node *left; /* tree to the left */
struct node *right; /* tree to the right */
char *word; /* word for this tree */
};
/* the top of the tree */
static struct node *root = NULL;
/*
* memory_error -- write error and die *
*/
void memory_error(void)
{
fprintf(stderr, "Error:Out of memory\n");
exit(8);
}
/*
* save_string -- save a string on the heap *
* *
* Parameters *
* string -- string to save *
* *
* Returns *
* pointer to malloc-ed section of memory with *
* the string copied into it. *
*/
char *save_string(char *string)
{
char *new_string; /* where we are going to put string */
new_string = malloc((unsigned) (strlen(string) + 1));
if (new_string == NULL)
memory_error();
strcpy(new_string, string);
return (new_string);
}
/*
* enter -- enter a word into the tree *
* *
* Parameters *
* node -- current node we are looking at *
* word -- word to enter *
*/
void enter(struct node **node, char *word)
{
int result; /* result of strcmp */
char *save_string(char *); /* save a string on the heap */
/*
* If the current node is null, we have reached the bottom
* of the tree and must create a new node.
*/
if ((*node) == NULL) {
/* Allocate memory for a new node */
(*node) = malloc(sizeof(struct node));
if ((*node) == NULL)
memory_error();
/* Initialize the new node */
(*node)->left = NULL;
(*node)->right = NULL;
(*node)->word = save_string(word);
return;
}
/* Check to see where the word goes */
result = strcmp((*node)->word, word);
/* The current node already contains the word, no entry necessary */
if (result == 0)
return;
/* The word must be entered in the left or right sub-tree */
if (result < 0)
enter(&(*node)->right, word);
else
enter(&(*node)->left, word);
}
/*
* scan -- scan the file for words *
* *
* Parameters *
* name -- name of the file to scan *
*/
void scan(char *name)
{
char word[100]; /* word we are working on */
int index; /* index into the word */
int ch; /* current character */
FILE *in_file; /* input file */
in_file = fopen(name, "r");
if (in_file == NULL) {
fprintf(stderr, "Error:Unable to open %s\n", name);
exit(8);
}
while (1) {
/* scan past the whitespace */
while (1) {
ch = fgetc(in_file);
if (isalpha(ch) || (ch == EOF))
break;
}
if (ch == EOF)
break;
word[0] = ch;
for (index = 1; index < sizeof(word); ++index) {
ch = fgetc(in_file);
if (!isalpha(ch))
break;
word[index] = ch;
}
/* put a null on the end */
word[index] = "\0";
enter(&root, word);
}
fclose(in_file);
}
/*
* print_tree -- print out the words in a tree *
* *
* Parameters *
* top -- the root of the tree to print *
*/
void print_tree(struct node *top)
{
if (top == NULL)
return; /* short tree */
print_tree(top->left);
printf("%s\n", top->word);
print_tree(top->right);
}
int main(int argc, char *argv[])
{
if (argc != 2) {
fprintf(stderr, "Error:Wrong number of parameters\n");
fprintf(stderr, " on the command line\n");
fprintf(stderr, "Usage is:\n");
fprintf(stderr, " words "file"\n");
exit(8);
}
scan(argv[1]);
print_tree(root);
return (0);
}

</source>

==Write structure into file==

<source lang="cpp">
/*
C & Data Structures
Published in Feb 2004 by CHARLES RIVER MEDIA
Author: P. S. Deshpande, O. G. Kakde
SKU: 1584503386
ISBN: 1584503386
*/

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define MAX 50

typedef struct {
char name[10];
int key;
} file_record;
/* this function adds the relatiuve addres to the index for a key */
void create_index(long index[], int key, long rel_add ) {
index[key] = rel_add;
}
/* this function writes a record to the file */
void write_rec(FILE *fp, file_record rec) {
fwrite(&rec,sizeof(rec),1,fp);
}
void main() {
long rel_add;
int key;
file_record frec;
long index[MAX];/* an index list*/
int n,i;
FILE *recfile=NULL,*ifile=NULL;
/* this initializes the index list to all ? */
for(i=0; i< MAX; i++)
index[i]= (-1);
recfile=fopen("mfile","w");
if(recfile == NULL) {
printf("Error in openeing file mfile\n");
exit(0);
}
rel_add = 0 ;
do {
printf(" Enter the data vlue and the key of the record to be added to file mfile\n");
scanf("%s %d",frec.name,&frec.key);
while(index[frec.key] != (-1)) {
printf(" A record with this key value already exist in a file enter record key value\n");
scanf("%s %d",frec.name,&frec.key);
}
create_index(index,frec.key,rel_add);
write_rec(recfile,frec);
rel_add = ftell(recfile);
/* this sets the relative address for the next record to be
the value of current file position pointer in bytes from
the beginning of the file */
printf("Enter 1 to continue adding records to the file\n");
scanf("%d",&n);
}while(n == 1);

ifile=fopen("index_file","w");

if(ifile == NULL) {
printf("Error in openeing file index_file\n");
exit(0);
}

fwrite(index,sizeof(index),1,ifile);/*writes the complete index into the index_file */
fclose(recfile);
fclose(ifile);
printf("Enter 1 if you want to retrieve a record\n");
scanf("%d",&n);

if( n == 1) {
ifile=fopen("index_file","r");
if(ifile == NULL) {
printf("Error in openeing file index_file\n");
exit(0);
}
fread(index,sizeof(index),1,ifile);

/* reads the complete index into the index list from the index_file*/
fclose(ifile);
recfile=fopen("mfile","r");

if(recfile == NULL) {
printf("Error in openeing file mfile\n");
exit(0);
}
}
printf("THE CONTENTS OF FILE IS \n");

while( (fread(&frec,sizeof(frec),1,recfile)) != 0)
printf("%s %d\n",frec.name,frec.key);

do {
printf("Enter the key of the record to be retrieved\n");
scanf("%d",&key);
rel_add = index[key]; /*gets the relative address of the record from index list */
if( (fseek(recfile,rel_add,SEEK_SET))!= 0) {
printf("Error\n");
exit(0);
}
fread(&frec,sizeof(frec),1,recfile);
printf("The data value of the retrieved record is %s\n",frec.name);
printf("Enter 1 if you want to retrieve a record\n");
scanf("%d",&n);
} while(n == 1);

fclose(recfile);
}

</source>

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