Unit5 (2)

typedef – to define new datatype bitfieds

‘ typedef ’ is a keyword,which allows you to struct playcard {
specify a new name for a datatype which is unsigned pips ;
already defined in c language program. unsigned suit ;
Syntax: };
typedef <datatype> <newname> Above structure occupies 4 bytes of
/* Re-defining int type as Integer type */ memory. But the member pips accepts a
typedef int Integer; value between 1 to 13 and the member suit
int main( ) { accepts any value of 0, 1, 2 and 3 .
Interger a ,b , sub; So we can create a more packed
a = 20,b = 10; representation of above structure with bitfields.
sub = a - b; struct playcard {
printf(“%d - %d = %d”, a, b, sub); unsigned pips : 4;
} unsigned suit : 2;
/* Defining structure with typedef to avoid };
repeated usage of struct keyword */ A bitfield is a set of adjacent bits within
a single machine word.
typedef struct { 4-bit field called pips that is capable of
int hours; storing the 16 values 0 to 15, and a 2-bit
int minutes; field called suit that is capable of storing
} TIME ; values 0, 1, 2, and 3. So the entire structure
int main( ) { variable occupies only one byte.
TIME t1, t2 , *t; Note : arrays of bit fields and a pointer to
t = (TIME *) calloc (10, sizeof( TIME )); address a bit field is not permitted.
}

Enumeration – a set of named integers, makes program more readable
Declaration of enumeration :
enum <enum_name> { member1, member2, …. …. …. } ;
Example :
enum option { YES, NO, CANCEL } ;
By default YES has value 0, NO has value 1 and CANCEL has 2.
enum direction { EAST = 1, SOUTH, WEST = 6, NORTH } ;
Now EAST has value 1, SOUTH has value 2, WEST has value 6, and NORTH has value 7.
Enumerated types can be converted implicitly or cast explicitly.
int x = WEST ; /* Valid. x contains 6. */
enum direction y ; y = (enum direction ) 2 ; /* Valid. Y contains SOUTH */

#include<stdio.h> #include<stdio.h>
int main() { enum color {RED = 1,ORANGE,GREEN };
int signal; int main() {
printf ("ttt MENU nt1.RED n"); enum color signal;
printf ("t2.ORANGEnt3.GREEN n“ ); printf ("ttt MENU nt1.RED n");
printf ("nt Enter the signal : “ ); printf ("t2.ORANGEnt3.GREENn");
scanf (“%d”, &signal ); printf ("nt Enter the signal : ");
switch(signal) scanf ("%d", &signal);
{ switch(signal) {
case 1: case RED:
printf(“t Stop and Wait!"); break; printf("t Stop and Wait!"); break;
case 2: case ORANGE:
printf(“t Ready to start!"); break; printf("t Ready to start!"); break;
case 3: case GREEN:
printf(“t Start and go!"); break; printf("t Start and go!"); break;
} }
} }

Console I / O Vs File I / O
 scanf( ) and printf( ) functions read and write data which always uses the
terminal (keyboard and screen) as the target.
 It becomes confusing and time consuming to use large volumes of data
through terminals.
 The entire data is lost when either program terminates or computer is
turned off.
 Some times it may be necessary to store data in a manner that can be
later retrieved and processed.
This leads to employ the concept of FILES to store data permanently
in the system.

File Operations
Record is logical group of data fields that
comprise a single row of information, which 1. Creating a new file
describes the characteristics of an object. 2. Opening an existing file
File is a set of records that can be accessed 3. Reading from a file
through the set of library functions. 4. Writing to a file
A File is a place on disk where a group of 5. Moving to a specific
related data ( records ) can be stored location in a file (seek)
6. Closing a file

A Stream acts as an interface between a program
and an input/output Device.

Stream is a Sequence of data bytes, which is used to read and write data to a file.
The streams that represent the input data of a program are known as Input Streams, where
as the streams that represent the output data of a program are known as Output Streams.
Input streams gets the data from different input devices such as keyboard and mouse and
provide input data to the program.
Output Streams obtain data from the program and write that on different Output Devices
such as Memory or print them on the Screen.

Types of Files
1.Text file : It can be thought of as a stream of characters that can be processed sequentially
and in forward direction only.
2.Binary file : It is collection of bytes like images.
3.Sequential File: Data stored sequentially, to read the last record of the file, we need to
traverse all the previous records before it. Ex: files on magnetic tapes.
4.Random Access File: Data can be accessed and modified randomly. We can read any record
directly. Ex : files on disks.

Steps involved using files

/*program to write and read data from file*/ 1. Declaring FILE pointer variable :
#include<stdio.h> Syntax :
void main() { FILE *file_pointer1;
FILE *fp;
char ch; 2. Open a file using fopen() function :
fp = fopen(“data.txt”, “w”); Syntax :
if(fp == NULL) { fp= fopen(“filename”,“mode of access”);
printf(“Cannot open file.”);
exit(0); 3. fputc() – Used to write a character to
} the file.
printf(“Type text ( to stop press ‘.’ ) : ”); Syntax :
while(ch != ‘.’) { fputc(character, file_pointer);
ch = getche();
fputc(ch,fp); 4. fgetc() – Used to read a character to the
} file.
fclose(fp); Syntax :
printf(“nContants read : “); fgetc(file_pointer);
fp = fopen(“data.txt”,”r”);
while(!feof(fp)) 5. Close a file using fclose() function :
printf(“%d”, fgetc(fp)); Syntax :
fclose(fp); fclose(file_pointer);
}

/* creating a new file */ file pointer used to handle files
int main(){
char ch;FILE *fp; filepointer=fopen(“filename”,”mode”);
printf("nEnter the textn");
printf("nt(Press ctrl+Z after
completing text)n"); putc(character,filepointer);
fp=fopen("str.txt","w");
while((ch=getchar())!=EOF) fclose(filepointer);
putc(ch,fp);
fclose(fp);
}

/* Reading the contents of existing file */ /* appending data to an existing file */
#include<stdio.h> int main() {
int main() { FILE *fp; char ch;
FILE *fp; printf("nEnter the textn");
char ch; printf("nt(Press ctrl+Z after
fp=fopen("str.txt","r"); completing text)n");
while((ch=getc(fp))!=EOF) fp=fopen("str.txt","a");
printf("%c",ch); while((ch=getchar())!=EOF)
fclose(fp); putc(ch,fp);
} fclose(fp);
}

r -- open a file in read mode r+ -- open a file in read and write mode
-- if file exits, the marker is positioned at -- if file exits, the marker is positioned
beginning. at beginning.
-- if file does not exist, error returned. -- if file does not exist, NULL returned.
w -- open a file in write mode w+ -- open a file in read and write mode
-- if file exits, all its data is erased. -- if file exits, all its data is erased.
-- if file does not exist, it is created. -- if file does not exist, it is created.
a -- open a file in append mode a+ -- open a file in read and append mode
-- if file exits, the marker is positioned -- if file exits, the marker is positioned
at end. at end.
-- if file does not exist, it is created. -- if file does not exist, it is created.

rb , wb , ab, rb+ , wb+ , ab+ are modes to operate a file as binary file.

int main( ) { /* Without using w+ */ /* open a file in read and write mode */
FILE *fp; char ch; int main( ) {
printf("nEnter the textn"); FILE *fp; char ch;
fp=fopen("str1.txt","w"); printf("nEnter the textn");
while((ch=getchar())!='n‘)putc(ch,fp); fp=fopen("str1.txt","w+");
fclose(fp); while((ch=getchar())!='n') putc(ch,fp);
fp=fopen("str1.txt","r"); rewind(fp);
while((ch=getc(fp))!=EOF) while((ch=getc(fp))!=EOF)
printf("%c",ch); printf("%c",ch);
fclose(fp); fclose(fp);
} }

File Input / Output Functions
fopen(fp, mode) Open existing file / Create new file
fclose(fp) Closes a file associated with file pointer.
closeall ( ) Closes all opened files with fopen()
fgetc(ch, fp) Reads character from current position and advances the pointer to
next character.
fprintf( ) Writes all types of data values to the file.
fscanf() Reads all types of data values from a file.
gets() Reads string from a file.
puts() Writes string to a file.
getw() Reads integer from a file.
putw() Writes integer to a file.
fread() Reads structured data written by fwrite() function
fwrite() Writes block of structured data to the file.
fseek() Sets the pointer position anywhere in the file
feof() Detects the end of file.
rewind() Sets the record pointer at the beginning of the file.
ferror() Reports error occurred while read/write operations
fflush() Clears buffer of input stream and writes buffer of output stream.
ftell() Returns the current pointer position.

Text files Vs Binary Files

/* Copying one binary file to other */ “rb”  open a file in read mode
“wb”  open a file in write mode
#include<stdio.h>
int main( ) “ab”  open a file in append mode
{ “rb+”  open a pre-existing file in read and
FILE *fs,*ft; write mode
char ch; “wb+” open a file in read and write mode
fs=fopen("pr1.exe","rb");
if(fs==NULL){ “ab+”  open a file in read and append mode
printf("nCannot Open the file"); Text File :
exit(0); i) Data are human readable characters.
} ii) Each line ends with a newline character.
ft=fopen("newpr1.exe","wb"); iii) Ctrl+z or Ctrl+d is end of file character.
if(ft==NULL) { iv) Data is read in forward direction only.
printf("nCannot open the file"); v) Data is converted into the internal format
fclose(fs); before being stored in memory.
exit( 0); Binary File :
} i) Data is in the form of sequence of bytes.
while((ch=getc(fs))!=EOF) ii) There are no lines or newline character.
putc(ch,ft); iii) An EOF marker is used.
fclose(fs); iv) Data may be read in any direction.
fclose(ft); v) Data stored in file are in same format that
} they are stored in memory.

Random Access File
int main() { ftell(file_pointer)
int n,i; -- returns the current position of file
char *str="abcdefghijklmnopqrstuvwxyz"; pointer in terms of bytes from the
FILE *fp = fopen("notes.txt","w"); beginning.
if(fp==NULL){ rewind(file-pointer)
printf("nCannot open file."); exit(0); -- moves the file pointer to the
} starting of the file, and reset it.
fprintf(fp,"%s",str); fseek(fileptr, offset, position)
fclose(fp); – moves the file pointer to the
fp = fopen("notes.txt","r"); location (position + offset)
printf("nText from position %d : nt“,ftell(fp)); position :
fseek(fp, 3 ,SEEK_SET); SEEK_SET – beginning of file
for(i=0; i < 5; i++) putchar(getc(fp)); SEEK_CUR – current position
printf("nText from position %d : nt“,ftell(fp)); SEEK_END – end of the file
fseek(fp, 4 ,SEEK_CUR);
for(i=0; i < 6; i++) putchar(getc(fp)); output :
fseek(fp, - 10 , SEEK_END); Text from position 3 :
printf("nText from position %d : nt“,ftell(fp)); defgh
for(i=0; i < 5; i++) putchar(getc(fp)); Text from position 12 :
printf("nCurrent position : %d",ftell(fp)); mnopqr
rewind(fp); Text from position 16 :
printf("nText from starting : nt"); qrstu
for(i=0;i < 8 ; i++) putchar(getc(fp)); Current position : 21
fclose(fp); Text from starting :
} abcdefgh

Formatted I / O /*Receives strings from keyboard
and writes them to file
/* using fscanf() and fprintf() functions */ and prints on screen*/
#include<stdio.h> #include<stdio.h>
int main( ) { int main( ) {
FILE *fp; FILE *fp;
int rno , i; char s[80];
float avg; fp=fopen(“poem.txt","w");
char name[20] , filename[15]; if(fp==NULL) {
printf("nEnter the filenamen"); puts("Cannot open file");exit(0);
scanf("%s",filename); }
fp=fopen(filename,"w"); printf("nEnter a few lines of text:n");
for(i=1;i<=3;i++) { while(strlen(gets(s))>0){
printf("Enter rno,name,average fputs(s,fp);
of student no:%d",i); fputs("n",fp);
scanf("%d %s %f",&rno,name,&avg); }
fprintf(fp,"%d %s %fn",rno,name,avg); fclose(fp);
} fp=fopen(“poem.txt","r");
fclose(fp); if(fp==NULL){
fp=fopen ( filename, "r“ ); puts("Cannot open file"); exit(0);
for(i=1;i<=3;i++) { }
fscanf(fp,"%d %s %f",&rno,name,&avg); printf("nContents of file:n");
printf("n%d %s %f",rno,name,avg); while(fgets(s,79,fp)!=NULL)
} printf("%s",s);
fclose(fp); fclose(fp);
} }

/* using putw() and getw() functions */ Standard I / O
#include<stdio.h>
int main( ) {
fputc() fgetc() Individual characters
FILE *fp1,*fp2; int i,n;
char *filename; fputs() fgets() Character Strings
clrscr(); fprintf() fscanf() Formatted ASCII
fp1=fopen("test.txt","w");
for(i=10;i<=50;i+=10) fwrite() fread() Binary files
putw(i,fp1); write() read() Low-level binary
fclose(fp1);
do {
printf("nEnter the filename : n");
Predefined Streams
scanf("%s",filename);
fp2=fopen(filename,"r");
if(fp2==NULL)
printf("nCannot open the file"); NAME MEANING
} while(fp2==NULL); stdin Standard input (from keyboard)
while(!feof(fp2)) {
stdout Standard output (to monitor)
n=getw(fp2);
if(n==-1) printf("nRan out of data"); stderr Standard error output (to monitor)
else printf("n%d",n);
} stdaux Standard auxiliary (both input and
fclose(fp2); output)
getch(); stdprn Standard printer output(to printer)
}

Handling Records (structures) in a File
struct player {
char name[40]; int age; int runs;
} p1,p2;
void main() {
int i ; FILE *fp = fopen ( "player.txt", "w");
if(fp == NULL) {
printf ("nCannot open file."); exit(0);
}
for(i=0;i<3;i++) {
printf("Enter name, age, runs of a player : ");
scanf("%s %d %d",p1.name, &p1.age,&p1.runs);
fwrite(&p1,sizeof(p1),1,fp);
}
fclose(fp);
fp = fopen("player.txt","r");
printf(“nRecords Entered : n");
for(i=0;i<3;i++) {
fread(&p2,sizeof(p2),1,fp);
printf("nName : %snAge : %dnRuns : %d",p2.name,p2.age,p2.runs);
}
fclose(fp);
}

Error Handling:
While operating on files, there may be a chance of having certain errors which will cause
abnormal behavior in our programs.
1)Opening an file that was not present in the system.
2)Trying to read beyond the end of file mark.
3)Device overflow.
4)Trying to use a file that has not been opened.
5)Trying to perform an operation on a file when the file is opened for another type of
operation.
6)Attempting to write to a write-protected file.

feof(fp) returns non-zero integer value if /* program on ferror( ) and perror ( ) */
we reach end of the file otherwise zero. #include<stdio.h>
ferror(fp) returns non-zero integer value int main(){
if an error has been detected otherwise FILE *fp;
zero char ch;
fp=fopen("str.txt","w");
perror(string)prints the string, a colon ch=getc(fp);
and an error message specified by the if(ferror(fp))
compiler perror(“Error Raised : ");
file pointer (fp) will return NULL if it else
cannot open the specified file. printf("%c",ch);
fclose(fp);
}

#include<stdio.h> fp will return NULL if unable to open
main(){ the file
FILE *fp1,*fp2;
int i,number;
char *filename; feof(fp) returns 1 if it reaches end of
fp1=fopen("TEST.txt","w"); file otherwise 0.
for(i=10;i<=50;i+=10)
putw(i,fp1);
fclose(fp1);
file:
printf("nEnter the filenamen");
scanf("%s",filename);
fp2=fopen(filename,"r");
Output:
if(fp2==NULL){ Enter the filename
printf("nCannot open the file"); TETS.txt
Cannot open the file
printf("nType File name again");
goto file;} Type the File name again
else{ Enter the filename
TEST.txt
for(i=1;i<=10;i++){
number=getw(fp2); 10
20
if(feof(fp2)){
printf("nRan out of data"); 30
break;} 40
50
else
printf("n%d",number); } } Ran out of data.
fclose(fp2);}

Structure of FILE pointer File Management Functions

Type: FILE rename(“old-filename",”new-filename");
File control structure for streams. -- It renames the file with the new name
typedef struct {
short level; remove(“filename")
unsigned flags; -- It removes the file specified (macro)
char fd;
unsigned char hold; unlink(“filename");
short bsize; -- It also removes the file name
unsigned char *buffer, *curp;
unsigned istemp; fcloseall();
short token; -- Closes all the opened streams in the
} FILE; program except standard streams.

File status functions fflush(file_pointer)
-- Bytes in the buffer transferred to file.
feof(file_pointer)
-- to check if end of file has been tmpfile ()
reached. -- creates a temporary file, to be deleted
ferror(file_pointer) when program is completed.
-- to check the error status of the file
clearerr(file_pointer) tmpnam(“filename”)
-- to reset the error status of the file -- creates a unique file name

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Unit5 (2)

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Unit5 (2)