C++ Strings

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C++ provides following 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 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 and initialization create 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 number of characters in the word "Hello."

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

If you follow the rule of array initialization, then you can write the above statement as follows −

char greeting[] = "Hello";

Following is the memory presentation of above defined string 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 initializes the array. Let us try to print above-mentioned string −

Example

#include <iostream>

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 compiled and executed, it produces the following result −

Greeting message: Hello

C Style String Functions

C++ supports a wide range of functions that manipulate null-terminated strings. These functions are defined in <string.h> header file.

Example

Following example makes use of few of the above-mentioned functions −

#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 code is compiled and executed, it produces result something as follows −

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.

Example of String Class

Let us check the following example −

#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 length of str3 after concatenation
   len = str3.size();
   cout << "str3.size() :  " << len << endl;

   return 0;
}

When the above code is compiled and executed, it produces result something as follows −

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

Creating a String

We can create string variables in two ways, using either of the following methods −

Creating String Using Character Arrays

We can declare strings using the C-type arrays in the format of characters. This is done using the following syntax −

Syntax

char variable_name[len_value] ;

Here, len_value is the length of the character array.

Example of Creating String using Character Array

In the following examples, we are declaring a character array, and assigning values to it.

#include <iostream>
using namespace std;

int main() { 
   char s[5]={'h','e','l','l','o'};
   cout<<s<<endl;
   return 0; 
}

Output

hello

Creating String using <string>

We can declare a String variable using the 'string' keyword. This is included in the <string> header file. The syntax of declaring a string is explained as follows −

Syntax

string variable_name = [value];

Here, [value] is an optional and can be used to assign value during the declaration.

Example

In the following examples, we are declaring a string variable, assigning a value to it.

#include <iostream>
using namespace std;

int main() { 
   string s="a merry tale";
   cout<<s;    
   return 0; 
}

Output

a merry tale

Traversing a String (Iterate Over a String)

We can iterate over a string in two ways −

Using looping statements

We can traverse a string using for loops, while loops and do while loops using a pointer to the first and the last index in the string.

Using iterators

Using range based loops, we can iterate over the string using iterators. This is achieved using ":" operator while running a range based loop.

Example of Iterating a String

The following example code shows string traversal using both of these methods −

#include <iostream>
using namespace std;

int main() {
   string s="Hey, I am at TP.";

   for(int i=0;i<s.length();i++){
      cout<<s[i]<<" ";
   }
   cout<<endl;

   for(char c:s){
      cout<<c<<" ";
   }

   return 0;
}

Output

H e y ,   I   a m   a t   T P . 
H e y ,   I   a m   a t   T P . 

Accessing Characters of String

We can access the characters of a string using both iterators and pointer to the indices of the string.

Example

The following example code shows how we can access the characters in a string −

#include <iostream>
using namespace std;

int main() {
   string s="Hey, I am at TP.";
   cout<<s<<endl;
   for(int i=0;i<s.length();i++){
     s[i]='A';
   }
   cout<<s<<endl;

   for(char &c:s){
      c='B';
   }
   cout<<s<<endl;

   return 0;
}

Output

Hey, I am at TP.
AAAAAAAAAAAAAAAA
BBBBBBBBBBBBBBBB

String Functions

String is an object of the <string> class, and hence, it has a variety of functions that users can utilize for a variety of operations. Some of these functions are as follows −

Length of a String

The length of a string is the number of characters present in the string. Hence, the string "apple" has a length of 5 characters and the string "hello son" has a length of 9 characters (including empty spaces). This can be accessed using the length() method in <string> header file.

Syntax

The syntax is explained as follows −

int len = string_1.length();

Example

#include <iostream>
#include <string>
using namespace std;

int main() {
   string x="hey boy";
   cout<<x.length()<<endl;

   return 0;
}

Output

7

String Concatenation

String concatenation is a way to add two strings together. This can be done using two ways −

Addition Operator

The addition operator is used to add two elements. In case of strings, the addition operator concatenates the two strings. This is clearly explained in the following example −

Example

#include <iostream>
#include <string>
using namespace std;

int main() {
   string x = "10";
   string y = "20";
   cout<<x+y<<endl;

   return 0;
}

Output

1020

This is different from integer addition. When we take two integers and add them using addition operator, we get the sum of the two numbers instead.

This is clearly explained in the following example −

Example

#include <iostream>
#include <string>
using namespace std;

int main() {
   int x = 10;
   int y = 20;
   cout<<x+y<<endl;

   return 0;
}

Output

30

Using string append() method

C++ is an object oriented programming language, and hence a string is actually an object, which contain functions that can perform certain operations on strings. We can use string append() method to append one string to another.

The syntax of this operation is as follows −

Syntax

string_1.append(string_2);

The usage of this method is depicted clearly in the following example −

Example

#include <iostream>
#include <string>
using namespace std;

int main() {
   string x="hey boy";
   string y=" now";
   x.append(y);
   cout<<x<<endl;

   return 0;
}

Output

hey boy now

String Input in C++

Strings can be taken as an input to the program, and the most common way to do this is by using cin method.

There are three methods to take a string as an input, and these methods are given as follows −

• cin
• getline()
• stringstream

Using cin Method

This is the simplest way to take a string as an input. The syntax is given as follows −

Syntax

cin>>string_name;

Example

#include <iostream>
using namespace std;

int main() {

   string s;
   cout << "Enter custom string : "<<endl;
   //enter the string here
   cin>>s;
   cout<<"The string is : "<<s;
}

Using getline() Method

The getline() method can be used to read a string from an input stream. This is defined in the <string> header file. The syntax of the above method is given as follows −

Syntax

getline(cin, string_name);

Example

#include <iostream>
using namespace std;

int main() {

   string s;
   cout << "Enter String as input : " << endl;
   getline(cin, s);
   //enter the string here
   cout << "Printed string is : " << s << endl;
   return 0;
}

Using stringstream

The stringstream class is used to take multiple strings as input, all at once. The syntax of the above method is given as follows −

Syntax

Stringstream object_name(string_name);

Example

#include <iostream>
#include <sstream>
#include <string>

using namespace std;

int main() {

   string s = "Hey, I am at TP";
   stringstream object(s);
   string newstr;
   // >> operator will read from the stringstream object
   while (object >> newstr) {
      cout << newstr << " ";
   }
   return 0;
}

Output

Hey, I am at TP