1. EPSII
59:006
Spring 2004

2. Makeup Exam Tuesday, April 13, 7:00 PM Room TBD Same procedure
You must your instructor with:
Class number of conflict
Instructors name
Time of class

3. Reading Data from a Sequential Access File
Reading a sequential access file
Create a FILE pointer, link it to the file to read
myPtr = fopen( "myFile.dat", "r" );
Use fscanf to read from the file
Like scanf, except first argument is a FILE pointer
fscanf( myPtr, "%d%s%f", &myInt, &myString, &myFloat );
Data read from beginning to end
File position pointer
Indicates number of next byte to be read / written
Not really a pointer, but an integer value (specifies byte location)
Also called byte offset
rewind( myPtr )
Repositions file position pointer to beginning of file (byte 0)

4. Initialize variables Link pointer to file Read data (fscanf) Print
1 /* Fig. 11.7: fig11_07.c
2 Reading and printing a sequential file */
3 #include <stdio.h> 4
5 int main()
6 {
7 int account;
8 char name[ 30 ];
9 double balance;
10 FILE *cfPtr; /* cfPtr = clients.dat file pointer */ 11
12 if ( ( cfPtr = fopen( "clients.dat", "r" ) ) == NULL )
printf( "File could not be opened\n" );
14 else {
printf( "%-10s%-13s%s\n", "Account", "Name", "Balance" );
fscanf( cfPtr, "%d%s%lf", &account, name, &balance ); 17
while ( !feof( cfPtr ) ) {
printf( "%-10d%-13s%7.2f\n", account, name, balance );
fscanf( cfPtr, "%d%s%lf", &account, name, &balance ); } 22
fclose( cfPtr );
24 } 25
26 return 0;
27 }
Initialize variables
Link pointer to file
Read data (fscanf)
Print
Close file
Program Output
Account Name Balance
Jones
Doe
White
Stone
Rich

5. Initialize variables Open file Input choice Scan files Print
1 /* Fig. 11.8: fig11_08.c
2 Credit inquiry program */
3 #include <stdio.h> 4
5 int main()
6 {
7 int request, account;
8 double balance;
9 char name[ 30 ];
10 FILE *cfPtr; 11
12 if ( ( cfPtr = fopen( "clients.dat", "r" ) ) == NULL )
printf( "File could not be opened\n" );
14 else {
printf( "Enter request\n"
" 1 - List accounts with zero balances\n"
" 2 - List accounts with credit balances\n"
" 3 - List accounts with debit balances\n"
" 4 - End of run\n? " );
scanf( "%d", &request ); 21
while ( request != 4 ) {
fscanf( cfPtr, "%d%s%lf", &account, name,
&balance ); 25
switch ( request ) {
case 1:
printf( "\nAccounts with zero "
"balances:\n" ); 30
while ( !feof( cfPtr ) ) { 32
Initialize variables
Open file
Input choice
Scan files
Print

6. Scan files Print 33 if ( balance == 0 )
printf( "%-10d%-13s%7.2f\n",
account, name, balance ); 36
fscanf( cfPtr, "%d%s%lf",
&account, name, &balance ); } 40
break;
case 2:
printf( "\nAccounts with credit "
"balances:\n" ); 45
while ( !feof( cfPtr ) ) { 47
if ( balance < 0 )
printf( "%-10d%-13s%7.2f\n",
account, name, balance ); 51
fscanf( cfPtr, "%d%s%lf",
&account, name, &balance ); } 55
break;
case 3:
printf( "\nAccounts with debit "
"balances:\n" ); 60
while ( !feof( cfPtr ) ) { 62
if ( balance > 0 )
printf( "%-10d%-13s%7.2f\n",
Scan files
Print

7. Close file 65 account, name, balance ); 66
fscanf( cfPtr, "%d%s%lf",
&account, name, &balance ); } 70
break; } 73
rewind( cfPtr );
printf( "\n? " );
scanf( "%d", &request ); } 78
printf( "End of run.\n" );
fclose( cfPtr );
81 } 82
83 return 0;
84 }
Close file

8. Program Output Enter request 1 - List accounts with zero balances
Enter request
1 - List accounts with zero balances
2 - List accounts with credit balances
3 - List accounts with debit balances
4 - End of run
? 1
Accounts with zero balances:
White
? 2
Accounts with credit balances:
Stone
? 3
Accounts with debit balances:
Jones
Doe
Rich
? 4
End of run.
Program Output

9. Reading Data from a Sequential Access File
Cannot be modified without the risk of destroying other data
Fields can vary in size
Different representation in files and screen than internal representation
1, 34, -890 are all ints, but have different sizes on disk
300 White Jones (old data in file)
If we want to change White's name to Worthington,
300 White Jones 32.87
300 Worthington 0.00ones 32.87
300 Worthington 0.00
Data gets overwritten

10. Sequential File I/O Example
Revisit substring generation and dictionary comparison
Previously:
%cat dict_file_name | ./a.out stringGoesHere Or
%./a.out < dict_file_name
With file I/O, we can now
Open dict_file_name and read words
Write words we find to a file
%a.out dict_file_name stringGoesHere

11. /* read in 2 strings from the command line --
1) dictionary file
2) string to search for
and try all contiguous permutations against dictionary */
#define NUM_WORDS 45427
#define MAX 30 // max word length
#include<stdio.h>
// prototypes
void get_chars(char *source, char *dest, int start, int len);
main(int argc, char* argv[]) {
char words[NUM_WORDS][MAX];
char temp[MAX];
int i = 0, j = 0, length = 0;
FILE *dict, *output;
if(argc < 3) {
printf("Useage: a.out dict_file string\n");
exit(1); }
if((dict = (fopen(argv[1],"r"))) == NULL) {
printf("Failed to open dictionary file %s\n",argv[1]);
else {
printf("Reading words from %s\n",argv[1]);
while(i<NUM_WORDS) {
fscanf(dict,"%s",words[i]);
printf("Reading word %d\r",i);
// for debugging
// printf("word = %s %d\n",words[i],i);
i++;

12. if((output = (fopen("results.txt","w"))) == NULL) {
printf("Failed to open results.txt\n");
exit(1); }
else {
printf("Writing results.txt\n");
for(length=1;length<=strlen(argv[2]);length++) {
for(i=0;i<=strlen(argv[2])-length;i++)
get_chars(argv[2],temp,i,length);
//printf("temp = %s\n",temp);
for(j=0;j<NUM_WORDS;j++) {
//printf("%s %s\n",temp,words[j]);
if(strcmp(temp,words[j])==0)
fprintf(output,"%s\n",temp); }
void get_chars(char *source, char *dest, int start, int len){
int i = 0;
int dstart = 0;
for(i=start,dstart=0;dstart<len;i++,dstart++)
dest[dstart] = source[i];
dest[dstart]='\0';

13. Illustration of Structures
Structures are datatypes (“things”) just like an “integer” is a datatype
Next 2 slides show
1) simple program with function (integer pass-by-value)
2) simple program with function (integer replaced with “struct record” -- still pass-by-value)
Structures may be nested

14. // prototype
int increment(int i);
main() {
int x = 5;
int result = 0;
result = increment(x);
printf("result = %d\n",result); }
// Function
int increment(int i) {
i = i + 1;
return(i);

15. struct record {
int a;
float b; };
// prototype
//int increment(int i); -- old prototype
struct record increment(struct record i);
main() {
//int x = 5;
struct record x = {5,5.5};
// same thing
x.a = 5;
x.b = 5.5;
//int result = 0;
struct record result;
result = increment(x);
printf("result = %d\n",result.a);
} // End main
// Function
struct record increment(struct record i) {
// i = i + 1;
i.a = i.a + 1;
return(i); }

16. Nested Structures Output: % ./a.out First = Homer
#include<stdio.h>
struct FLnames {
char first[10];
char last[10]; };
struct record {
int id; // just a plain old int
struct FLnames name;
char city[20];
main() {
struct record employee;
employee.id = 18;
strcpy(employee.name.first,"Homer");
strcpy(employee.name.last,"Simpson");
strcpy(employee.city,"Iowa City");
printf("first = %s\n",employee.name.first); }
Output:
% ./a.out
First = Homer