C Programming: Strings Standard Functions

STRINGS STANDARD FUNCTIONS

 

The 'C' compiler provides the following string handling functions.

Function: Purpose

strlen(): Used to find the length of the string.

strcpy(): Used to copy one string to another.

strcat(): Used to combine two strings.

strcmp(): Used to compare characters of two strings (difference between small and capital letters).

strlwr(): Used to convert strings into lower case.

strupr(): Used to convert strings into upper case.

strdup(): Used to duplicate a string.

strrev(): Used to reverse a string.

strncpy(): Used to copy first 'n' characters of one string into another.

strncmp(): Used to compare first 'n' characters of two strings.

strcmpi(): Used to compare two strings without regarding the case.

strnicmp(): Used to compare first 'n' characters of two strings without regarding the case.

stricmp():Compares two strings (Not difference between small and capital letters).

strchr():Determines first occurrence of a given character in a string.

strrchr():Determines last occurrence of a given character in a string.

strstr():Determines first occurrence of a given string in another string.

strncat():Appends source string to destination string upto specified length.

strnset():Sets specified number of characters of string with a given argument or symbol.

strspn():Finds up to what length two strings are identical.

strpbrk(): Searches the first occurrence of the character in a given string and then it displays the string starting from that character.

The commonly used string manipulation functions are as follows:

1. The strlen() function

This function is used to count and return the number of characters present in a string.

Syntax: var = strlen(string);

Description:

var - Is the integer variable, which accepts the length of the string.

String - Is the string constant or string variable, in which the length is going to be found. The counting ends with first null (\0)char.

Example: Program using strlen() function.

/* Program using strlen() function */

#include <stdio.h>

#include <conio.h>

main()

{

          char name[] = "MUNI";

          int len1,len2;

          len1 = strlen(name); /* To find the length of the string */

          len2 = strlen("VRB");

          printf("\n string length of %s is %d",name,len1);

          printf("\n_string length of %s is %d,", "VRB",len2);

}  /* main */

OUTPUT

String length of MUNI is 4

String length of VRB is 3

EXPLANATION: The above program refers to check the length of the string. Here the character type name[] holds the element 'Muni', it is passed to variable len1. The len2 variable holds the elements of 'VRB' 'strlen' function detect the length of string len1 and len2 and print the result as above mentioned.

Here, while calculating the length of the string by using the strlen() the '\0' null character is not taken into consideration.

2. The strcpy() function

This function is used to copy the contents of one string to another and it almost works like string assignment operator.

Syntax: strepy (string1, string2);

Description:

String1 is the destination string

String2 is the source string

The contents of string2 is assigned to the contents of string1. Where string2 may be character array variable or string constant.

Example:

char str[]="MUNI";

char str2[]= "LAK";

strcpy(str1, str2);

Where the contents of str2 are copied into the strl and the contents of strl is replaced with new one.

Example

char str1[10];

strcpy(str1, "LAK");

Here, the string constants are copied to the string variable strl.

Example: Program using strcpy() function

/* Program using strcpy() function */

#include <stdio.h>

main ()

{

          char source = "MUNI"; *Local definitions */

          char target[10];

          strcpy(target,source);   /* string copy */

          printf("\n Source string is %s", source);

          printf("\n Target string is %s", target);

} /* main */

OUTPUT

Source string is MUNI'

Target string is MUNI

EXPLANATION: In the program the character type variable source contain a string "MUNI". The variable target[] is declared as a character type. Here the strcpy() function copy the source string "MUNI" into target string. Now the variable target also contain the string "MUNI" and print the variable source and target.

3. The strcat() function

The strcat() function is used to concatenate or combine, two strings together and forms a new concatenated string.

Syntax: strcat(string1, string2);

Description: string1 and string2 are character type arrays or string constants.

When the above strcat() function is executed, string2 is combined with string1 and it removes the null character (\0) of string1 and places string2 from there.

Example:

            strcat("MUNI”, “LAK”)

Yields  MUNILAK

            char strl="MUNI”

            char str2="LAK"

            strcat(str1, str2)

Yields MUNILAK.

Example: Program using strcat() function

/* Program using strcat() function */

#include <stdio.h>

main()

{

        /* Local definitions */

        char source[]="Ramesh";

        char target[10]= "Babu";

        /* Statements */

        strcat(source, target); /* string concatenate function */

        printf("\nSource string is %d", source);

        printf("\nTarget string is %s", target);

} /* main */

OUTPUT

Source string is Ramesh Babu

Target string is Babu

EXPLANATION: In the program source[] is a character variable which holds the data "Ramesh" similarly target[] is a character variable which holds the data "Babu", The strcat() combines both strings and stores in the variable "source" finally print the variable "source" and "target" as mentioned above.

4. The strcmp() function

This is a function which compares two strings to find out whether they are same or different. The two strings are compared character by character until the end of one of the string is reached. If the two strings are identical, strcmp() returns a value zero. If they are not equal, it returns the numeric difference between the first non‒matching characters.

Syntax: strcmp(string1, string2);

Description: string1 and string2 are character type arrays or string constants.

Example: Program using strcmp() function.

/* Program using strcmp() function */

#include <stdio.h>

#include <conio.h>

main()

{

* Local definitions */

char name[] = "Kalai",

char name[] = "Malai";

int i,j,k;

/* Statements */

i= strcmp(name, "Kalai"); /* string compare function */

j= strcmp(namel, name);

k=strcmp(name, "Kalai mani");

printf("\n %d %d %d", i, j, k );

} /* main */

OUTPUT

0   1   6

EXPLANATION: In the first strcmp(,) the two strings are same, so it returns zero value. In the second, the first character of the two string is unmatched. So the difference between ASCII value is printed. In the third one, the strings are unmatched. The blank space is unmatched with '\0' character. So the ASCII value difference between '\0' and 'space' is printed.

5. The strrev() function

The strrev() function is used to reverse a string. This function takes only one argument and return one argument.

The general form of strrev() function is,

Syntax: strrev(string);

Description: string are characters type arrays or string constants.

Example: Program using strrev() function

/* Program using strrev() function */

#include <stdio.h>

main()

{

        char y[30]; /* Local definition */

        printf ("Enter the string :");

        gets(y);

        printf ("The string reversed is :%s", strrev(y));

} /* main */

INPUT: Enter the string : book

OUTPUT: The string reversed is: koob

EXPLANATION: The function strrev() is used to print the string in reverse order. The program gets the input book then reverse that string as koob and prints the result as output.

6. The strchr() Function

The strchr() function returns a pointer to the first occurrence of the low‒ order byte of ch in the string pointed to by str. If no match is found, a null pointer is returned.

Syntax: char *strchr(const char *str, int ch);

Description: Where Char is string, ch is character

Example: Program prints the string is a test

#include <stdio.h>

#include <string.h>

int main(void)

{

         char *p; c='g'

         p = strchr("C Language", ");

         printf(p); printf("%d",c);

         return 0;

}

OUTPUT

C Language

5

7. The strlwr() function

The strlwr() function converts all the uppercase characters in that string to lowercase characters. The resultant from strtwr() is stored in the same string.

Syntax: strlwr(string name);

Description: Where string name is string

Example: Program using strlwr() function

#include <stdio.h>

#include <string.h>

int main()

{

char strl]="LOWER CASE";

puts(strlwr(strl)); //converts to lowercase and displays it.

return 0;

}

OUTPUT

lower case

8. The strupr() function

The strupr() function converts all the lowercase characters in that string to uppercase characters. The resultant from strupr() is stored in the same string.

Syntax: strlwr(string _name);

Description: Where string_name is string

Example: Program using strupro function

#include <stdio.h>

#include <string.h>

int main()

{

        char str[]="upper case";

        puts(strupr(str1)); //converts to lowercase and displays it.

        return 0;

}

OUTPUT

UPPER CASE