C Characters and Strings

8/6/2019 C Characters and Strings

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2000 Prentice Hall, Inc. All rights reserved.

Chapter 8 - Characters and Strings

Outline8.1 Introduction

8.2 Fundamentals of Strings and Characters

8.3 Character Handling Library8.4 String Conversion Functions

8.5 Standard Input/Output Library Functions

8.6 String Manipulation Functions of the String Handling

Library

8.7 Comparison Functions of the String Handling Library

8.8 Search Functions of the String Handling Library8.9 Memory Functions of the String Handling Library

8.10 Other Functions of the String Handling Library


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8.1 Introduction

Introduce some standard library functions Easy string and character processing

Programs can process characters, strings, lines of text, and blocks

of memory

These techniques used to make Word processors

Page layout software

Typesetting programs


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8.2 Fundamentals of Strings and

Characters

Characters Building blocks of programs

Every program is a sequence of meaningfully grouped

characters

Character constant - an int value represented as a character

in single quotes

'z' represents the integer value ofz


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Characters (II)

Strings Series of characters treated as a single unit

Can include letters, digits, and certain special characters (*, /,

$)

String literal (string constant) - written in double quotes

"Hello"

Strings are arrays of characters

String a pointer to first character

Value of string is the address of first character


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Characters (III)

String declarations Declare as a character array or a variable of type char *

char color[] = "blue";

char *colorPtr = "blue";

Remember that strings represented as character arrays endwith '\0'

color has 5 elements


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Characters (IV)

Inputting strings Use scanf

scanf("%s", word);

Copies input intoword[], which does not need & (because a

string is a pointer) Remember to leave space for'\0'


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8.3 Character Handling Library

Character Handling Library Includes functions to perform useful tests and manipulations

of character data

Each function receives a character (an int) orEOF as an

argument


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8.3 Character Handling Library (II)

In

rototype escription

int is

igit int c ) Returns true i c is a digit and false other ise.intisalpha(intc ) Returns true i c is a letter and false other ise.intisalnum(intc ) Returns true i c is a digit or a letter and false other ise.intisx

igit(intc ) Returns true i c is a hexadecimal digit character and false other ise.intislower(intc ) Returns true i c is a lo ercase letter andfalse other ise.intisupper(intc ) Returns true i c is an uppercase letter; false other ise.inttolower(intc ) I c is an uppercase letter, tolower returns c as a lo ercase letter. Other ise,tolower

returns the argument unchanged.

inttoupper(intc ) I c is a lo ercase letter,toupper returns c as an uppercase letter. Other ise,toupperreturns the argument unchanged.

intisspace(intc ) Returns true i c is a hite-space characterne line ('\n'), space (''), orm eed('\f'), carriage return ('\r'), horizontal tab ('\t'), or vertical tab ('\v')and

false other ise

intiscntrl(intc ) Returns true i c is a control character and false other ise.intispunct(intc ) Returns true i c is a printing character other than a space, a digit, or a letter and false

other ise.

intisprint(intc ) Returns true value i c is a printing character including space ('') and falseother ise.

intisgraph(intc ) Returns true i c is a printing character other than space ('') and false other ise.


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Outline

1. Load header

2. Perform tests

3. Print

1 /*Fig. 8.2:fig08_02.c

2 Usingfunctionsisdigit,isalpha,isalnum, andisxdigit*/

3 #include

4 #include

5

6 int main()

7 {8 printf("%s\n%s%s\n%s%s\n\n","Accordingtoisdigit:",

9 isdigit('8' ) ? "8 is a ":"8 isnot a ","digit",

10 isdigit('#' ) ? "#is a ":

11 "#isnot a ","digit" );

12 printf("%s\n%s%s\n%s%s\n%s%s\n%s%s\n\n",

13 "Accordingtoisalpha:",

14 isalpha('A' ) ? "Ais a ":"Aisnot a ","letter",

15 isalpha('b' ) ? "bis a ":"bisnot a ","letter",

16 isalpha('&' ) ? "& is a ":"& isnot a ","letter",

17 isalpha('4' ) ? "4 is a ":

18 "4 isnot a ","letter" );

19 printf("%s\n%s%s\n%s%s\n%s%s\n\n",

20 "Accordingtoisalnum:",

21 isalnum('A' ) ? "Ais a ":"Aisnot a ",

22 "digitor a letter",

23 isalnum('8' ) ? "8 is a ":"8 isnot a ",

24 "digitor a letter",

25 isalnum('#' ) ? "#is a ":"#isnot a ",

26 "digitor a letter" );

27 printf("%s\n%s%s\n%s%s\n%s%s\n%s%s\n%s%s\n",

28 "Accordingtoisxdigit:",

29 isxdigit('F' ) ? "Fis a ":"Fisnot a ",

30 "hexadecimal digit",

31 isxdigit('J' ) ? "Jis a ":"Jisnot a ",



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Outline

Program Output

33 isxdigit('7' ) ? "7 is a ":"7 isnot a ",


35 isxdigit('$' ) ? "$is a ":"$isnot a ",


37 isxdigit('f' ) ? "fis a ":"fisnot a ",

38 "hexadecimal digit" );

39 return 0;

40 }

Accordingtoisdigit:

8 is a digit#isnot a digit

Accordingtoisalpha:Ais a letter

bis a letter& isnot a letter4 isnot a letter

Acc

ording

tois

alnum:

Ais a digitor a letter8 is a digitor a letter

#isnot a digitor a letter

Accordingtoisxdigit:

Fis a hexadecimal digitJisnot a hexadecimal digit7 is a hexadecimal digit

$isnot a hexadecimal digitfis a hexadecimal digit


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8.4 String Conversion Functions

Conversion functions In(general utilities library)

Convert strings of digits to integer and floating-point values

rototype escription

doubleatof(constchar *n tr) Converts the string n tr to double.intatoi(constchar*n tr ) Converts the string n tr to int.longatol(constchar*n tr ) Converts the string n tr to long int.doublestrtod(constchar*n tr ,char**endPtr ) Converts the string nPtr to double. longstrtol(constchar*nPtr,char

**endPtr,intbase ) Converts the string nPtr to long .

unsignedlongstrtoul( constchar*nPtr,char**endPtr,intbase ) Converts the string nPtr to unsignedlong .


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Outline

1. Initialize variable

2. Convert string

2.1 Assign to variable

3. Print

Program Output

1 /*Fig. 8.6:fig08_06.c

2 Using atof*/

3 #include

4 #include

5

6 int main()7 {

8 double d;

9

10 d = atof("99.0" );

11 printf("%s%.3f\n%s%.3f\n",

12 "Thestring\"99.0\" convertedto doubleis", d,

13 "The convertedvalue dividedby2is",

14 d/2.0 );

15 return 0;

16 }

Thestring"99.0" convertedto doubleis99.000

The convertedvalue dividedby2is49.500


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8.5 Standard Input/Output Library

Functions

Functions in Used to manipulate character and string data

F u n c t io n p ro t o t y p e Fu n c t io n d e sc r ip t io n

intgetchar(v oid ); Inpu ts the nex t cha rac te r rom thes tandard inpu t and retu rns i t a s an in teger.

char*gets(char*s ); Inpu ts cha rac te rs rom the s tandard inpu tinto the array s u ntil a ne lin e o r e nd-o -

i le character is encountered.t e rmina t ing nu l l charac te r is append ed tothe a r ray .

int putchar( intc ); r in ts the character s tored in c .

intputs(constchar*s ); r in ts the s t r ing s o llo ed b y a n e lin echaracter .

intsp rintf(char*s,constchar*format,... );

quiva len t to p rintf , excep t the ou tpu tis s tored in the array s ins tead o

pr int ing i t on the screen.

intsscanf(char*s,constchar*format,... );

quiva len t to scanf , excep t the inpu t i sread rom the a r ray s ins tead o

read ing i t rom the keyboard .


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Outline

1. Initialize variables

2. Input

3. Print

3.1 Function definition

(note recursion)

1 /*Fig. 8.13:fig08_13.c

2 Usinggets andputchar */

3 #include

4

5 int main()

6 {

7 charsentence[ 80 ];

8 voidreverse(const char *const );

9

10 printf("Enter a lineoftext:\n" );

11 gets(sentence );

12

13 printf("\nThelineprintedbackwardsis:\n" );

14 reverse(sentence );

15

16 return 0;

17 }

18

19 voidreverse(const char *const sPtr )

20 {

21 if (sPtr[ 0 ] == '\0' )

22 return;

23 else {

24 reverse( &sPtr[ 1 ] );

25 putchar(sPtr[ 0 ] );

26 }

27 }

Enter a lineoftext:Characters and Strings

Thelineprintedbackwardsis:

sgnirtS dna sretcarahC

reverse calls itself using substrings of

the original string. When it reaches the

'\0' character it prints usingputchar


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8.6 String Manipulation Functions of the

String Handling Library

String handling library has functions to Manipulate string data

Search strings

Tokenize strings

Determine string length

Func tio n p rototype Func tio n de sc rip tio n

char*strcpy(char*s1,constchar*s2 )

Copies string s2 into array s1. The value o s1is

returned.

char*strncpy(char*s1,constchar*s2,size_tn )

Copies at most n characters o string s2 into array

s1. The value o s1 is returned.

char*strcat(char*s1,constchar*s2 )

ppends string s2 to array s1. The irst character o

s2 over rites the terminating nullcharacter o s1.

The value o s1 is returned.

char*strncat(char*s1,constchar*s2,size_tn )

ppends at most n characters o string s2 to array

s1. The irst character o s2 over rites the

terminating null character o s1. The value o s1 is

returned.


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Outline


2. Function calls

3. Print

Program Output

1 /*Fig. 8.19:fig08_19.c

2 Usingstrcat andstrncat*/

3 #include

4 #include

5

6 int main()7 {

8 char s1[ 20 ] = "Happy";

9 char s2[] = "New Year ";

10 char s3[ 40 ] = "";

11

12 printf("s1 = %s\ns2 = %s\n",s1,s2 );

13 printf("strcat(s1,s2 ) = %s\n",strcat(s1,s2 ) );

14 printf("strncat(s3,s1, 6 ) = %s\n",strncat(s3,s1, 6 ) );

15 printf("strcat(s3,s1 ) = %s\n",strcat(s3,s1 ) );

16 return 0;

17 }

s1 = Happy

s2 = New Year

strcat(s1,s2 ) = HappyNew Year

strncat(s3,s1, 6 ) = Happy

strcat(s3,s1 ) = HappyHappyNew Year


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8.7 Comparison Functions of the String

Handling Library

Comparing strings Computer compares numeric ASCII codes of characters in string

Appendix D has a list of character codes

intstrcmp( con

st char *

s1, con

st char *

s2 );

Compares string s1 to s2

Returns a negative number (s1 < s2), zero (s1 == s2), or apositive number (s1 >s2)

intstrncmp( const char *s1, const char *s2,size_tn );

Compares up to n characters of string s1 to s2

Returns values as above


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8.8 Search Functions of the String

Handling Library

Func t i n roto t p e Func tion esc ription

char *strchr( const char *s,int c );

Locates the first occurrence of characterc in string s. Ifc is found, a pointer to c in

s is returned. therwise, a NULL pointer is returned.size_tstrcspn( const char*s1, const char *s2 );

Determines and returns the length of the initial segment of string s1 consisting of

characters not contained in strings2.size_tstrspn( const char

*s1, const char *s2 );Determines and returns the length of the initial segment of strin g s1 consisting only

of characters contained in string s2.char *strpbrk( const char*s1, const char *s2 );

Locates the first occurrence in string s1 of any character in string s2. If a character

from string s2 is found, a pointer to the character in string s1 is returned. ther-

wise, a NULL pointer is returned.char *strrchr( const char *s,int c );

Locates the last occurrence ofc in string s. Ifc is found, a pointer to c in string s is

returned. therwise, a NULL pointer is returned.char *strstr( const char *s1,

const char *s2 );

Locates the first occurrence in string s1 of string s2. If the string is found, a pointer

to the string in s1 is returned. therwise, a NULL pointer is returned.char *strtok( char *s1, constchar *s2 );

A sequence of calls to strtok breaks string s1 into tokens logical pieces such

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.


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Outline


2. Function calls

3. Print

Program Output

1 /*Fig. 8.27:fig08_27.c

2 Usingstrspn*/

3 #include

4 #include

5

6 int main()

7 {

8 const char *string1 = "Thevalueis3.14159";

9 const char *string2 = "aehilsTuv";

10

11 printf("%s%s\n%s%s\n\n%s\n%s%u\n",

12 "string1 = ",string1,"string2 = ",string2,

13 "Thelength oftheinitialsegmentofstring1",

14 "containingonly charactersfromstring2 = ",

15 strspn(string1,string2 ) );

16 return 0;

17 }

string1 = Thevalueis3.14159

string2 = aehilsTuv

Thelength oftheinitialsegmentofstring1containingonly charactersfromstring2 = 13


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Outline


2. Function calls

3. Print

Program Output

1 /*Fig. 8.29:fig08_29.c

2 Usingstrtok */

3 #include

4 #include

5

6 int main()

7 {

8 char string[] = "Thisis a sentence with 7 tokens";

9 char *tokenPtr;

10

11 printf("%s\n%s\n\n%s\n",

12 "Thestringtobetokenizedis:",string,

13 "Thetokens are:" );

14

15 tokenPtr = strtok(string,"" );

1617 while (tokenPtr != NULL ) {

18 printf("%s\n",tokenPtr );

19 tokenPtr = strtok(NULL,"" );

20 }

21

22 return 0;

23 }

Thestringtobetokenizedis:Thisis a sentence with 7 tokens

Thetokens are:Thisis

a

sentencewith

7tokens


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8.9 Memory Functions of the String-

handling Library

Memory Functions

In

Manipulate, compare, and search blocks of memory

Can manipulate any block of data

Pointer parameters are void*

Any pointer can be assigned to void*, and vice versa

void* cannot be dereferenced

Each function receives a size argument specifying the numberof bytes (characters) to process


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8.9 Memory Functions of the String-

handling Library (II)

Prototype escription

void*memcpy(void*s1,constvoid*s2,size_tn )

Copies n characters rom the object pointed to bys2 into the object

pointed to by s1. pointer to the resulting object is returned.

void*memmove(void*s1,constvoid*s2,

size_tn )

Copies n characters rom the object pointed to bys2 into the object

pointed to by s1. The copy is per ormed as i the characters are irstcopied rom the object pointed to bys2 into a temporary array, and

then copied rom the temporary array into the object pointed to bys1. pointer to the resulting object is returned.

intmemcmp(constvoid*s1,constvoid*s2,size_tn )

Compares the irstn characters o the objects pointed to bys1 and

s2. The unction returns0, less than 0, or greater than 0 i s1 is

equal to, less than or greater thans2, respectively.void*memchr(constvoid*s,intc,size_t

n )

Locates the irst occurrence o c (converted to unsignedchar) in

the irst n characters o the object pointed to bys. I c is ound, apointer to c in the object is returned. Other ise,0 is returned.

void*memset(void*s,intc,size_tn ) Copies c (converted to unsignedchar) into the irstn characterso the object pointed to bys. pointer to the result is returned.

" b ect" refers to a block of data


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Outline


2. Function calls

3. Print

Program Output

1 /*Fig. 8.32:fig08_32.c

2 Usingmemmove*/

3 #include

4 #include

5

6 int main()

7 {

8 char x[] = "Home SweetHome";

9

10 printf("%s%s\n",

11 "Thestringin arrayxbeforememmoveis:",x );

12 printf("%s%s\n",

13 "Thestringin arrayx after memmoveis: ",

14 memmove(x, &x[ 5 ],10 ) );

15

16 return 0;

17 }

Thestringin arrayxbeforememmoveis:Home SweetHomeThestringin arrayx after memmoveis: SweetHomeHome


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8.10 Other Functions of the String Handling

Library

char *strerror(interrornum );

Creates a system-dependent error message based on errornum

Returns a pointer to the string

size_tstrlen( const char *s );

Returns the number of characters (before NULL) in string s


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Outline

1. Function call

2. Print

Program Output

1 /*Fig. 8.37:fig08_37.c

2 Usingstrerror */

3 #include

4 #include

5

6 int main()

7 {

8 printf("%s\n",strerror(2 ) );

9 return 0;

10 }

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C Characters and Strings