String Handling in C++

String Handling in c++ provides two types of string representations:

  • The C-style character string.
  • The string class type introduced with Standard C++.

The C-Style Character String:

The C-style character string originated within the C language and continues to be supported within C++. This character string is actually a one-dimensional array of characters which is terminated by a null character ‘\0’. Thus a null-terminated string contains the characters that comprise the string followed by a null.

The following declaration creates a string consisting of the word “Hello”. To hold the null character at the end of the array, the size of the character array containing the string is one more than the no. of characters in the word “Hello.”

char greeting[6] = {'H', 'e', 'l', 'l', 'o', '\0'};

If we follow the rule of array initialization, then we can write the above statement also as follows:

char greeting[] = "Hello";

Following is the memory representation of above defined string in C or C++:

String Presentation in C/C++
Actually, you do not place the null character at the end of a string constant. The C++ compiler automatically places the ‘\0’ at the end of the string when it initialized the array. Let us try to print above-mentioned string as:

#include<iostream.h>

using namespace std;

int main ()
{
   char greeting[6] = {'H', 'e', 'l', 'l', 'o', '\0'};

   cout << "Greeting message: ";
   cout << greeting << endl;

   return 0;
}

When the above code is executed, it produces result will be as follows:

Greeting message: Hello

C++ supports a wide range of functions that manipulate null-terminated strings:

S.N.Function & Purpose
1strcpy(s1, s2);Copies string s2 into string s1.
2strcat(s1, s2);Concatenates string s2 onto the end of string s1.
3strlen(s1);Returns the length of string s1.
4strcmp(s1, s2);Returns 0 if s1 and s2 are the same; less than 0 if s1<s2; greater than 0 if s1>s2.
5strchr(s1, ch);Returns a pointer to the first occurrence of character ch in string s1.
6strstr(s1, s2);Returns a pointer to the first occurrence of string s2 in string s1.

Following example makes used with the above-mentioned functions in a program:

#include <iostream>
#include <cstring>

using namespace std;

int main ()
{
   char str1[10] = "Hello";
   char str2[10] = "World";
   char str3[10];
   int  len ;

   // copy str1 into str3
   strcpy( str3, str1);
   cout << "strcpy( str3, str1) : " << str3 << endl;

   // concatenates str1 and str2
   strcat( str1, str2);
   cout << "strcat( str1, str2): " << str1 << endl;

   // total lenghth of str1 after concatenation
   len = strlen(str1);
   cout << "strlen(str1) : " << len << endl;

   return 0;
}

When the above program is executed, the result will be:

strcpy( str3, str1) : Hello
strcat( str1, str2): HelloWorld
strlen(str1) : 10

The String Class in C++:

The standard C++ library provides a string class type that supports all the operations mentioned above, additionally much more functionality. We will study this class in C++ Standard Library but for now let us check following example:

At this point, you may not understand this example because so far we have not discussed Classes and Objects. So can have a look and proceed until you have understanding on Object Oriented Concepts.

#include <iostream>
#include <string>

using namespace std;

int main ()
{
   string str1 = "Hello";
   string str2 = "World";
   string str3;
   int  len ;

   // copy str1 into str3
   str3 = str1;
   cout << "str3 : " << str3 << endl;

   // concatenates str1 and str2
   str3 = str1 + str2;
   cout << "str1 + str2 : " << str3 << endl;

   // total lenghth of str3 after concatenation
   len = str3.size();
   cout << "str3.size() :  " << len << endl;

   return 0;
}

The above code is executed, it produces result the result as follows :

str3 : Hello
str1 + str2 : HelloWorld
str3.size() :  10
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