1. Introduction to Computer Programming Lecture 18 Binary Files
Assist.Prof.Dr. Nükhet ÖZBEK
Ege University
Department of Electrical&Electronics Engineering

2. RECALL: Text File Handling in C
ITCS 102 Computer Programming
RECALL: Text File Handling in C
Step 0: Include stdio.h
Step 1: Declare a file handler (a.k.a. file pointer) as FILE * for each file
Step 2: Open file using fopen()
Step 3: Check if file is opened successfully
Step 4a: Use fscanf() for input
Step 4b: Use fprintf() for output
Step 5: Close file using fclose()
Dr. Bekir KARLIK

3. Binary Files
When text files are used for storage of data, a program must spend extra effort to convert the stream of characters from an input file into integers and vice versa for output files
If the file is not to be read by a human, we can avoid this unnecessary translation

4. Binary Files
A binary file is a file created by executing a program that stores directly in the file the computer’s internal representation of each file component

5. Binary File Example FILE *binaryp; int i;
binaryp = fopen(“nums.bin”, “wb”);
for (i = 2; i <= 500; i+=2)
fwrite(&i, sizeof(int), 1, binaryp);
fclose(binaryp);

6. Binary file declaration
Binary File Example
Binary file declaration
is the same as
text file declaration
FILE *binaryp;
int i;
binaryp = fopen(“nums.bin”, “wb”);
for (i = 2; i <= 500; i+=2)
fwrite(&i, sizeof(int), 1, binaryp);
fclose(binaryp);

7. ‘b’ character is used to
Binary File Example
‘b’ character is used to
denote that the file is
a binary file
FILE *binaryp;
int i;
binaryp = fopen(“nums.bin”, “wb”);
for (i = 2; i <= 500; i+=2)
fwrite(&i, sizeof(int), 1, binaryp);
fclose(binaryp);

8. fclose function is used
Binary File Example
FILE *binaryp;
int i;
binaryp = fopen(“nums.bin”, “wb”);
for (i = 2; i <= 500; i+=2)
fwrite(&i, sizeof(int), 1, binaryp);
fclose(binaryp);
fclose function is used
just as for text files

9. a different stdio library
Binary File Example
FILE *binaryp;
int i;
binaryp = fopen(“nums.bin”, “wb”);
for (i = 2; i <= 500; i+=2)
fwrite(&i, sizeof(int), 1, binaryp);
fclose(binaryp);
a different stdio library
function is used

10. contents are to be copied
fwrite function
fwrite function has 4 input parameters
fwrite(&i, sizeof(int), 1, binaryp);
Address of the first
memory cell whose
contents are to be copied
to the file

11. fwrite function fwrite function has 4 input parameters
fwrite(&i, sizeof(int), 1, binaryp);
Number of bytes to copy
to the file for one
component

12. sizeof operator
sizeof operator can be applied to any data type to find the number of bytes used for storage of the data type
sizeof operator can be applied to both built-in and user-defined types
E.g.
printf(“An integer requires %d bytes”,sizeof(int));

13. Number of values to write
fwrite function
fwrite function has 4 input parameters
fwrite(&i, sizeof(int), 1, binaryp);
Number of values to write
to the file

14. Pointer to the file which
fwrite function
fwrite function has 4 input parameters
fwrite(&i, sizeof(int), 1, binaryp);
Pointer to the file which
is opened for writing
before

15. Notes on fwrite
It is possible to write the contents of an entire array using just one fwrite call
E.g.,
int score[10]; …
fwrite(score, sizeof(int), 10, binaryp);

16. fread function fread function also requires four parameters
Address of the first memory cell to fill
Size of one value
Maximum number of elements to copy from the file into memory
File pointer to a binary file opened in mode “rb”
fread function returns an integer indicating how many elements it copied from the file

17. Notes It is important not to mix file types
A binary file created or written using fwrite must be read using fread
A text file created or written using fprintf must be read using fscanf

18. Binary File Example
/* FREAD.C: This program opens a file named FREAD.OUT and writes 25 characters to the file. It then tries to open the file and read in 25 characters. If the attempt succeeds, the program displays the number of actual items read. */
#include <stdio.h>
int main( void ) {
FILE *stream;
int list[25];
int i, numread, numwritten;
/* Open file in binary mode: */
stream = fopen( "fread.out", "wb" );
if( stream == NULL ) {
printf( "Problem opening the file\n" );
return 1; }

19. Binary File Example (cntd)
for ( i = 0; i < 25; i++ ) list[i] = i;
/* Write 25 characters to stream */
numwritten = fwrite( list, sizeof( int ), 25, stream );
printf( "Wrote %d items\n", numwritten );
fclose( stream );
stream = fopen( "fread.out", "rb" );
if( stream == NULL ) {
printf( "File could not be opened\n" );
return 2; }

20. Binary File Example (cntd)
/* Attempt to read in 25 characters */
numread = fread( list, sizeof( int ), 25, stream );
printf( "Number of items read = %d\n", numread );
fclose( stream );
return 0; }

21. Structures and Binary Files
Structures can also be written to and read from binary files using fwrite and fread functions
Structures are written or read as a “package” with one function
Structure arrays can also be written with one function

22. Data I/O Using Text and Binary Files
Suppose we have a structure like the following:
typedef struct {
char name[10];
double diameter;
int moons; …
} planet_t;

23. Data I/O Using Text and Binary Files (Opening for reading)
Text File I/O
FILE *fp;
fp = fopen(“planets.txt”,”r”);
Binary File I/O
fp = fopen(“planets.bin”,”rb”);

24. Data I/O Using Text and Binary Files (Opening for writing)
Text File I/O
FILE *fp;
fp = fopen(“planets.txt”,”w”);
Binary File I/O
fp = fopen(“planets.bin”,”wb”);

25. Data I/O Using Text and Binary Files (Read one structure from file)
Suppose:
planet_t p;
Text File I/O
fscanf(fp,”%s %lf %d”,
p.name,&(p.diameter),&(p.moons));
Binary File I/O
fread(&p,sizeof(planet_t), 1, fp);

26. Data I/O Using Text and Binary Files (Read N structure from file)
Suppose:
planet_t p[N];
Text File I/O
for(i=0; i < N; i++)
fscanf(fp,”%s %lf %d”,
p[i].name,&(p[i].diameter),&(p[i].moons);
Binary File I/O
fread(p,sizeof(planet_t), N, fp);

27. Data I/O Using Text and Binary Files (Write one structure to file)
Suppose:
planet_t p;
Text File I/O
fprintf(fp,”%s %lf %d”,
p.name,p.diameter,p.moons);
Binary File I/O
fwrite(&p,sizeof(planet_t), 1, fp);

28. Data I/O Using Text and Binary Files (Write N structure from file)
Suppose:
planet_t p[N];
Text File I/O
for(i=0; i < N; i++)
fprintf(fp,”%s %lf %d”, p[i].name, p[i].diameter, p[i].moons);
Binary File I/O
fwrite(p,sizeof(planet_t), N, fp);

29. Data I/O Using Text and Binary Files (Closing)
Text File I/O
fclose(fp);
Binary File I/O

30. Two other file operations functions that may be useful
int remove(const char *filename);
Defined in <stdio.h>
Deletes the file specified by filename
int rename(const char *oldname, const char *newname);
Changes the name of a file from oldname to newname

31. Disadvantages of Binary Files
A binary file created on one computer is rarely readable on another type of computer
Since a binary file can be read only by a specialized computer program, a person cannot proofread the file
A binary file cannot be created or modified in a word processor, so a program that expects binary file input cannot be tested until the program that produces the binary file is complete

32. Random Files
Random file access refers to the ability to read or modify information directly at any given position in a file
This is done by getting and setting a file position indicator, which represents the current access position in the file associated with a given stream

33. Random Access Files
Records in a file created with fprintf are not necessarily the same length
Individual records of a randomly accessed file are normally fixed in length and may be accessed directly (thus quickly) without searching through records
This makes random access files appropriate for systems that require rapid access to specific data

34. Random Access Files
Every record in a randomly accessed file normally has the same length
The exact location of a record relative to the beginning of the file can be calculated as a function of the record key
100 bytes
100 bytes
100 bytes
100 bytes
100 bytes
etc.
100
200
300
400
500
byte
offsets

35. Random Access Files Normally, structs are used in random access files
Example program
A program to process bank accounts
Each record has an account number used as the record key, a last name, a first name and a balance
First a random access file of 100 records is created with 0 for account number, NULL for first name and last name and 0.0 for balance

36. Example – creating a random accessed file (from Deitel)
/* Creating a randomly accessed file sequentially */
#include <stdio.h>
#define NRECORDS 100
struct clientData {
int acctNum;
char lastName[15];
char firstName[15];
double balance; };

37. Example – creating a random accessed file (from Deitel)
int main() {
int i;
struct clientData blankClient = {0, "", "", 0.0};
FILE *cfPtr;
if ( (cfPtr = fopen("credit.dat", "wb")) == NULL)
printf("File could not be opened.\n");
for (i = 1 ; i <= NRECORDS ; i++)
fwrite(&blankClient, sizeof(struct clientData), 1, cfPtr);
fclose(cfPtr);
return 0; }

38. Example – writing data randomly to a random accessed file (from Deitel)
#include <stdio.h>
#define NRECORDS 100
struct clientData {
int acctNum;
char lastName[15];
char firstName[15];
double balance; };
int main() {
struct clientData client = {0, "", "", 0.0};
FILE *cfPtr;

39. Example – writing data randomly to a random accessed file (from Deitel)
if ( (cfPtr = fopen("credit.dat", "r+b")) == NULL)
printf("File could not be opened.\n");
printf("Enter account number (1 to %d, 0 to end input)\n? ", NRECORDS);
scanf("%d", &client.acctNum);

40. Example – writing data randomly to a random accessed file (from Deitel)
while(client.acctNum != 0) {
printf("Enter lastname, firstname, balance\n? ");
fscanf(stdin, "%s%s%lf", client.lastName, client.firstName, &client.balance);
fseek(cfPtr, (client.acctNum - 1) * sizeof(struct clientData), SEEK_SET);
fwrite(&client, sizeof(struct clientData), 1, cfPtr);
printf("Enter account number (1 to %d, 0 to end input)\n? ", NRECORDS);
scanf("%d", &client.acctNum); }
fclose(cfPtr);
return 0;

41. fseek function int fseek (FILE *stream, long int offset, int whence)
offset is the number of bytes from location whence in the file pointed to by stream
whence can have one of three values
SEEK_SET – seek starts at the beginning of the file
SEEK_CUR – seek starts at the current location in the file
SEEK_END – seek starts at the end of the file

42. Example – reading data from a random accessed file (from Deitel)
#include <stdio.h>
struct clientData {
int acctNum;
char lastName[15];
char firstName[15];
double balance; };
int main() {
struct clientData client = {0, "", "", 0.0};
FILE *cfPtr;

43. Example – reading data from a random accessed file (from Deitel)
if ( (cfPtr = fopen("credit.dat", "rb")) == NULL)
printf("File could not be opened.\n");
printf("%-6s%-16s%-11s%10s\n","Acct", "Last Name", "First Name", "Balance");
while(fread(&client, sizeof(struct clientData), 1, cfPtr))
if(client.acctNum != 0)
printf("%-6d%-16s%-11s%10.2f\n", client.acctNum, client.lastName, client.firstName, client.balance);
fclose(cfPtr);
return 0; }