String Functions

The string functions can analyze and transform null terminated strings.  In order to manipulate null terminated strings header file <cstring> is included in the program. This header file provides the same functionality as string.h in C. Some of the commonly used string functions are: -

• strcat(s1, s2) - It concatenates two strings. It concatenates s2 at the end of s1.
• strcmp (s1, s2) – It is used to compare strings. It returns 0 if they are equal and less than 0 if s1<s2 and greater than 0 if s1>s2.
• strlen(s1) – It returns the length of the string s1.
• strcpy(s1, s2) - It copies s2 into s1.
• strncat(s1, s2, n) -   It appends substring to the string. It takes first n characters of string s2 and appends s1.
• strncmp(s1,s2,n) – It compares first n characters of string s1 with first n characters of string s2.
• strchr(s1, ch) – Finds character ch in string s1.  It returns the pointer at the first occurrence of ch.
• strstr(s1, s2) – Finds substring s2 in s1. It returns a pointer at the first occurrence of s1.

Here is a program which illustrates the working of string functions.

#include<iostream>

#include<cstring>

using namespace std;

int main ()

{

      int l;

      char name[40]=" Tom is a good boy";

      char name1[40]="Mary is a good girl";

      char stri[40];

      l=strlen(name);

      cout << "The lenght of the string 1 is : " << l <<  endl;

      if(strstr(name,"good"))

      {

                  cout << "Substring good appears in string 1 " << endl;

      }

      if(strchr(name1,'M'))

      {

                  cout << "Character M appears in sting 1 " <<  endl;

      }

      if(strcmp(name,name1)>0)

      {

                  cout << "String 2 appears after string" << endl;

      }

      strcpy(stri,name1);

      cout << "The copied string  : " << stri << endl;

      strncat(stri,name,4);

      cout << " The modified string : " << stri << endl;

      if(strncmp(stri,name1,3)==0)

      {

                  cout << "First 3 characters of two strings are equal" << endl;

      }

      strcat(name,"  ");

      strcat(name,name1);

      cout << name << endl;

      return(0);

}

The result of the program is:-

The statement

#include<cstring>

includes a header file <cstring> into the program. The statement

       l=strlen(name);

computes the length of the string name. The function strlen(name)  returns the length of the string name. The length of the string is 18. The statement

      if(strstr(name,"good"))

checks whether substring “good” appears in the string name. The function strstr(name,”good”) returns true as “good” appears in string name. The statement

      if(strchr(name1,'M'))

checks whether character ‘M’ appears in string name1. The function strchr(name1,’M’) returns true as character ‘M’ appears in string name1. The statement

                        if(strcmp(name,name1)>0)

compares two strings name and name1. It returns false as string name< string name1.

The statement

      strcpy(stri,name1);

copies content of string name1 into string stri. The statement

            strncat(stri,name,4);

concatenates first 4 letters of string name to string stri. The statement

            if(strncmp(stri,name1,3)==0)

compares first  3 characters of string name1 with first 3 characters of string stri. It   returns true as first 3 characters of name1 and stri are same. The statement

      strcat(name,"  ");

concatenates whitespace at the end of the string name. The statement

            strcat(name,name1);

concatenates content of string name1 at the end of  string name.