1. Introduction to Programming
Lecture 17

2. String Handling

3. String Manipulation Functions

4. Character

5. ASCII

6. 1 byte = 8 bits

7. Example 1 #include<iostream.h> main ( ) { int i ; char c ;
for( i = 0; i < 256 ; i ++ )
c = i ;
cout << i << “\t” << c <<endl ; }

8. #include<ctype.h>
Header File
ctype.h
#include<ctype.h>
Storage Requirements for Text and Binary Modes
Storage Requirements for Text and Binary Modes
for an Integer:
for an Integer:
Page 32
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The fwrite() Function
The fwrite() Function
size_t fwrite (void *ptr, size_t size, size_t nmemb,
size_t fwrite (void *ptr, size_t size, size_t nmemb,
FILE *fp);
FILE *fp);
fwrite() writes, from the address pointed to by ptr,
fwrite() writes, from the address pointed to by ptr,
up to nmemb elements whose size is specified by
up to nmemb elements whose size is specified by
size, to the file pointed by fp
size, to the file pointed by fp
fwrite() returns the number of elements
fwrite() returns the number of elements
successfully written, which will be less than nmemb
successfully written, which will be less than nmemb
only if a write error is encountered.
only if a write error is encountered.
double earnings[10];
double earnings[10];
fwrite(earnings,sizeof(double),10,fp);
fwrite(earnings,sizeof(double),10,fp); 32 32
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The fread() Function
The fread() Function
size_t fread(void *ptr, size_t size, size_t nmemb,
size_t fread(void *ptr, size_t size, size_t nmemb,
FILE *fp);
FILE *fp);
fread() reads, into the array pointed to by ptr, up to
fread() reads, into the array pointed to by ptr, up to
nmemb elements whose size is specified by size,
nmemb elements whose size is specified by size,
form the file pointed to by fp.
form the file pointed to by fp.
fread() returns the number of elements
fread() returns the number of elements
successfully read, which may be less than nmemb
successfully read, which may be less than nmemb
is a read error or end-of-file is encountered.
is a read error or end-of-file is encountered. 33 33
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Writing file data using block I/O functions
Writing file data using block I/O functions
#include <stdio.h>
#include <stdio.h>
typedef struct {
typedef struct {
char name[20];
char name[20];
int serial_code;
int serial_code;
int amount;
int amount;
float
float
cost;
cost;
} component;
} component;
main(void)
main(void)
{ component comp_data;
{ component comp_data;
FILE
FILE
*fp;
*fp;
char
char
filename[80];
filename[80];
int numofcomp;
int numofcomp;
int i;
int i;
printf("Enter the file name: ");
printf("Enter the file name: ");
gets(filename);
gets(filename); 34 34
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if ((fp = fopen(filename, "wb")) == NULL) {
if ((fp = fopen(filename, "wb")) == NULL) {
printf("can't open file \n");
printf("can't open file \n");
exit(1);
exit(1);
}printf("Enter the number of components: ");
}printf("Enter the number of components: ");
scanf("%d", &numofcomp);
scanf("%d", &numofcomp);
for (i=0; i<numofcomp; i++) {
for (i=0; i<numofcomp; i++) {
printf("Name of the component: ");
printf("Name of the component: ");
gets(comp_data.name);
gets(comp_data.name);
printf("Serial code of the component: ");
printf("Serial code of the component: ");
scanf("%d", &comp_data.serial_code);
scanf("%d", &comp_data.serial_code);
printf("Amount of the component: ");
printf("Amount of the component: ");
scanf("%d", &comp_data.amount);
scanf("%d", &comp_data.amount);
printf("Cost of each component: ");
printf("Cost of each component: ");
scanf("%f", &comp_data.cost);
scanf("%f", &comp_data.cost);
fwrite(&comp_data, sizeof(comp_data), 1, fp);
fwrite(&comp_data, sizeof(comp_data), 1, fp);
}fclose(fp);
}fclose(fp);
return 0;
return 0; } } 35 35
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12.5 Random Access
12.5 Random Access
Random Access: fseek() and ftell()
Random Access: fseek() and ftell()
fseek, ftell: All the previous I/O functions do reading
fseek, ftell: All the previous I/O functions do reading
and writing sequentially, i.e. read the 1st datum, 2rd
and writing sequentially, i.e. read the 1st datum, 2rd
datum, 3rd datum ..., etc.
datum, 3rd datum ..., etc.
fseek
fseek
and
and
ftell
ftell
help doing
help doing
I/O in non-sequential manner, i.e. read the 10th
I/O in non-sequential manner, i.e. read the 10th
datum, then go back and read the 2nd datum.
datum, then go back and read the 2nd datum. 36 36
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File position pointer
File position pointer
The system keeps a file position pointer for
The system keeps a file position pointer for
each open file.
each open file.
It indicates the location in the file at
It indicates the location in the file at
which data will be read or written.
which data will be read or written.
file position marker
file position marker
......
......
Disk
Disk 37 37
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The fseek() Function
The fseek() Function
The function prototype of
The function prototype of
fseek()
fseek() is is
int fseek(FILE *fp, long int offset, int mode);
int fseek(FILE *fp, long int offset, int mode); * *
fseek()
fseek()
returns
returns
if OK, and
if OK, and -1 -1
if there is an error.
if there is an error. * *
offset
offset
tells how far to move from the starting point
tells how far to move from the starting point
(depending on the mode). It can be +ve (move
(depending on the mode). It can be +ve (move
forward) or -ve (move backward) or 0.
forward) or -ve (move backward) or 0. * *
mode
mode
identifies the starting point. In stdio.h, the
identifies the starting point. In stdio.h, the
following constants can be assigned to mode:
following constants can be assigned to mode:
Mode
Mode
Measure offset from
Measure offset from
SEEK_SET
SEEK_SET
Beginning of file
Beginning of file
SEEK_CUR
SEEK_CUR
Current position
Current position
SEEK_END
SEEK_END
End of file
End of file 38 38
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The ftell() Function
The ftell() Function
The function prototype of
The function prototype of
ftell()
ftell() is is
long int ftell(FILE *fp);
long int ftell(FILE *fp);
returns the current file location.
returns the current file location.
The rewind() Function
The rewind() Function
The function prototype of
The function prototype of
rewind()
rewind() is is
void rewind(FILE *fp);
void rewind(FILE *fp);
Resets the file position marker to the beginning of
Resets the file position marker to the beginning of
the file. This is equivalent to
the file. This is equivalent to
fseek(fp, 0L, SEEK_SET);
fseek(fp, 0L, SEEK_SET); 39 39
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/* reverse.c - displays a file in reverse order */
/* reverse.c - displays a file in reverse order */
#include <stdio.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdlib.h>
#define CNTL_Z '\032'
#define CNTL_Z '\032'
/* eof marker in DOS textfiles */
/* eof marker in DOS textfiles */
{ int main(int argc, char *argv[])
{ int main(int argc, char *argv[])
char ch;
char ch;
FILE *fp;
FILE *fp;
long count, last;
long count, last;
if ((fp=fopen(argv[1],"rb"))== NULL) {
if ((fp=fopen(argv[1],"rb"))== NULL) {
printf("reverse can't open %s\n", argv[1]);
printf("reverse can't open %s\n", argv[1]);
exit(1);
exit(1); } }
fseek(fp,0L, SEEK_END);
fseek(fp,0L, SEEK_END);
/* goto eof */
/* goto eof */
last=ftell(fp);
last=ftell(fp);
for (count=1L; count<=last; count++) {
for (count=1L; count<=last; count++) {
fseek(fp,-count,SEEK_END);
fseek(fp,-count,SEEK_END);
ch=getc(fp);
ch=getc(fp);
if (ch!=CNTL_Z && ch!= '\r')
if (ch!=CNTL_Z && ch!= '\r')
putchar(ch);
putchar(ch);
}fclose(fp);
}fclose(fp);
return(0);
return(0); 40 40 } }

9. ctype Functions int isspace ( int c ) int isdigit ( int c )
int iscntrl ( int c )
int ispunct ( int c )
int isprint ( int c )
int isgraph ( int c )
int isdigit ( int c )
int isalpha ( int c )
int isalnum ( int c )
int isxdigit ( int c )
int islower ( int c )
int isupper ( int c )
int tolower ( int c )
int toupper ( int c )

10. isdigit ( ) Function
int isdigit ( int c ) ;

11. isalpha ( ) Function
int isalpha ( int c ) ;

12. isalnum ( ) Function
int isalnum ( int c ) ;

13. islower ( ) Function
int islower ( int c ) ;

14. isupper ( ) Function
int isupper ( int c ) ;

15. tolower ( ) Function
int tolower ( int c ) ;

16. toupper ( ) Function
int toupper ( int c ) ;

17. getchar ( ) ;

18. cout << “Please enter a character string then press enter”;
while ( ( c = getchar ( ) ) != ‘\n’ ) {
if ( islower ( c ) )
lc ++ ;
else if ( isupper ( c ) )
uc ++ ;
else if (isdigit ( c ) )
dig ++;
else if ( isspace ( c ) )
ws ++ ;
else if ( ispunct ( c ) )
pun ++ ;
else
oth ++ ; }

19. String Conversion Functions
double atof ( char * str )
int atoi (char * str )
long atol (char * str )

20. atoi ( ) Function
char str [ ] ;
int age ;
age = atoi ( str ) ;

21. atof ( ) Function
12.89

22. atof ( ) Function
char str [ ] ;
double dVar ;
dVar = atof ( str ) ;

23. int main (int agrc, char **agrv )
‘argc’ stands for a count of the number of arguments
‘argv’ stands for a vector of arguments

24. String Functions

25. String Manipulation Functions
Function prototype
Function description
char *strcpy( char *s1,
const char *s2 )
Copies string s2
into array s1
. The value of is
returned.
char *strncpy( char *s1,
const char *s2, size_t n)
Copies at most n
characters of string .
The value of
is returned.
int strcmp( const char *s1,
const char *s2 );
Compares string to
Returns a negative number if
s1 < s2
, zero if
s1 == s2
or a positive number if
s1 > s2
int strncmp( const char *s1,
const char *s2,
size_t n ); Co
mpares up to
Returns values as above
char *strcat( char *s1,
Appends string
to array
. The first character of
overwrites the terminating null
character of
char
*strncat( char *s1,
const char *s2, size_t n )
Appends at most
The first character of
overwrites the terminating
null character of

26. int sum ;
int sum_even ;
int sum_odd ;
myStrcpy ( ) ;

27. String Manipulation Functions
char * strcpy (char *s1 , const char *s2 ) ;
char * strncpy ( char *s1 , char *s2 , int n ) ;
char * strcat (char *s1 , char *s2 ) ;
char * strncat ( char *s1 , char *s2 , int n ) ;

28. int strcmp (const char *s1 , const char *s2 ) ;
strcmp ( ) Function
int strcmp (const char *s1 , const char *s2 ) ;

29. int strncmp ( const char *s1 , const char *s2 , int n ) ;
strncmp ( ) Function
int strncmp ( const char *s1 , const char *s2 , int n ) ;

30. int strlen ( const char *s ) ;
strlen ( ) Function
int strlen ( const char *s ) ;

31. Search Functions

32. Search Functions Function prototype Function description
char *strchr( const char *s,
int c );
Locates the first occurrence of character c
in string s
. If
is found, a pointer to in
is returned. Otherwise, a
NULL
pointer is returned.
size_t strcspn( const char
*s1,
const char *s2 );
Determines and returns the length of the initial segment of string s1
consisting of
characters not contained in string s2 .
size_t strspn( const char
*s1, const char *s2 );
Determines and returns the length of the initial segment of strin g
consisting only
of characters contained in string
char *strpbrk( const char
Locates the first occurrence in string
of any character in string
. If a character
from string
is found, a pointer to the character in stri ng
is returned. Other -
wise, a
char *strrchr( const char *s,
Locates the last occurrence of is
returned. Otherwise, a
char *strstr( co
nst char *s1,
Locates the first occurrence in string s1
of string s2
. If the string is found, a pointer
const char *s2 );
to the string in s1
is re
turned. Otherwise, a
NULL
pointer is returned.
char *strtok( char *s1, const
A sequence of call
s to
strtok
breaks string s1
into “tokens” —
logical pieces such
char *s2 );
as words in a line of text —
separated by characters contained in string s2
. The first
call contains s1
as the first argument, and subsequent calls to continue tokenizing
the same string contain
NULL
as the first argument. A pointer to the current token is
returned by each call. If there are no more tokens when the function is called,
NULL
is returned.

33. This is a test
“ “ wrong
‘ ‘ right
NULL