STRING IN C++

STRING in C++

• WAYS TO DEFINE STRING IN C++
• HOW TO TAKE STRING INPUT IN C++
• C++ STRING FUNCTIONS
• POINTERS IN STRINGS

std::string Class These are new types of strings represented in C++ as a std::string class defined by header file. It offers many advantages over traditional C-style chords, such as dynamic size, limb functions, etc.

 

Syntax:

std::string str("Hello India");

for     example,

#include <iostream>

using namespace std;

int main()

{

                  string str("Hello India");

                  cout << str;

                  return 0;

}

Output

Hello India

 Ways to define a string in C++

Strings can be defined in C++ in several ways. Strings can be accessed from the standard library using the String class. Arrays of characters can also be used to define strings. String provides many functions such as search and manipulation which are commonly used methods. Although this method is less advanced than the String class, it is still widely used because it is more efficient and easier to use. The following are ways to define a string in C++:

   Using the String Keyword

·       Using C-Style Strings.

 1)      Using string keyword

It is easier to define a string with the string keyword instead of the array keyword because it is easier to write and understand.

 Syntax

                   string s = "Hello India";

                  string s("Hello India");

let us try understanding this by a C++ program 

 #include <iostream>

using namespace std;

int main()

{

                  string s = "Hello India";

                  string str("Hello India");

                  cout << "s = " << s << endl;

                  cout << "str = " << str << endl;

                  return 0;

}

Output

s = Hello India

str = Hello India

2) Using C-style string 

Using C-style string library functions such as strcpy(), strcmp(), and strcat() to define 

strings. This method is more complex and not as widely used as the other two, but it 

can be useful when dealing with legacy code or when you need performance.

char s[] = {'s', 't', 'b', '\0'};

char s[4] = {'s', 't', 'b', '\0'};

char s[4] = "stb";

char s[] = "stb";

let us try a C++ program to understand C-style string 

#include <iostream>

using namespace std;

int main()

{

                  char s1[] = { 'c', 'd', 'e', '\0' };

                  char s2[4] = { 'c', 'd', 'e', '\0' };

                  char s3[4] = "cde";

                  char s4[] = "cde";

                  cout << "s1 = " << s1 << endl;

                  cout << "s2 = " << s2 << endl;

                  cout << "s3 = " << s3 << endl;

                  cout << "s4 = " << s4 << endl;

                   return 0;

}

 Output

 

s1 = stb

s2 = stb

s3 = stb

s4 = stb

 How to take string input in C++

Entering a string means getting a string from the user. in C++. We have different user inputs that depend on the string. The most common way is to type the cin keyword using the C++ extraction operator (>>). Ways to take a string as input:

·       cin

·       Getline

·       stringstream.

 

1)      Using cin

 

Syntax

                  cin>>s;

let us understand this by a C++ program

#include <iostream>

using namespace std;

int main() 

{

                  string s;

                  cout<<"Enter String"<<endl;

                  cin>>s;

                  cout<<"String is: "<<s<<endl;

                  return 0;

}

Output

Enter string : Hello India

String is : Hello India

 

    2)  Using get line()

The C++ function getline() is used to read a string from the input stream. It is declared as <string> header file.

Syntax

                  getline(cin,s);

 let us understand this by a C++ program 

#include <iostream>

using namespace std;

int main()

{

                  string s;

                  cout << "Enter String" << endl;

                  getline(cin, s);

                  cout << "String is: " << s << endl;

                  return 0;

}

 Output

Enter the string: Hello India

String is: Hello India

 

3)      Using stringstream

 

Syntax

                  stringstream stringstream_object(string_name);

let us understand this by a C++ program 

#include <iostream>

#include <stream>

#include<string>

using namespace std;

 int main()

{

                  string s = " Hello Everyone  ";

                  stringstream obj(s);

                  // string to store words individually

                  string temp;

                  // >> operator will read from the stringstream object

                  while (obj >> temp) {

                                     cout << temp << endl;

                  }

                  return 0;

}

Output

Hello

Everyone

 

To pass a string to functions

 

Just as we pass an array to a function, C++ strings can be passed to functions as character arrays. Here is a sample program.

 

Let us try by a C++ program

 

#include <iostream>

using namespace std;

 

void print_string(string s)

{

              cout << "Passed String is: " << s << endl;

              return;

}

int main()

{

              string s = "Hello India";

              print_string(s);

              return 0;

}

Output

The passed string is: Hello India

 

C++ String Functions

 

Function	Description
int compare(const string& str)	It is used to compare two string objects.
int length()	It is used to find the length of the string.
void swap(string& str)	It is used to swap the values of two string objects.
string substr(int pos,int n)	It creates a new string object of n characters.
int size()	It returns the length of the string in terms of bytes.
void resize(int n)	It is used to resize the length of the string up to n characters.
string& replace(int pos,int len,string& str)	It replaces a portion of the string that begins at character position pos and spans len characters.
string& append(const string& str)	It adds new characters at the end of another string object.
char& at(int pos)	It is used to access an individual character at specified position pos.
int find(string& str,int pos,int n)	It is used to find the string specified in the parameter.
int find_first_of(string& str,int pos,int n)	It is used to find the first occurrence of the specified sequence.
int find_first_not_of(string& str,int pos,int n )	It is used to search the string for the first character that does not match with any of the characters specified in the string.
int find_last_of(string& str,int pos,int n)	It is used to search the string for the last character of specified sequence.
int find_last_not_of(string& str,int pos)	It searches for the last character that does not match with the specified sequence.
string& insert()	It inserts a new character before the character indicated by the position pos.
int max_size()	It finds the maximum length of the string.
void push_back(char ch)	It adds a new character ch at the end of the string.
void pop_back()	It removes a last character of the string.
string& assign()	It assigns new value to the string.
int copy(string& str)	It copies the contents of string into another.
char& back()	It returns the reference of last character.
Iterator begin()	It returns the reference of first character.
int capacity()	It returns the allocated space for the string.
const_iterator cbegin()	It points to the first element of the string.
const_iterator cend()	It points to the last element of the string.
void clear()	It removes all the elements from the string.
const_reverse_iterator crbegin()	It points to the last character of the string.
const_char* data()	It copies the characters of string into an array.
bool empty()	It checks whether the string is empty or not.
string& erase()	It removes the characters as specified.
char& front()	It returns a reference of the first character.
string&  operator+=()	It appends a new character at the end of the string.
string& operator=()	It assigns a new value to the string.
char operator[](pos)	It retrieves a character at specified position pos.
int rfind()	It searches for the last occurrence of the string.
iterator end()	It references the last character of the string.
reverse_iterator rend()	It points to the first character of the string.
void shrink_to_fit()	It reduces the capacity and makes it equal to the size of the string.
char* c_str()	It returns pointer to an array that contains null terminated sequence of characters.
const_reverse_iterator crend()	It references the first character of the string.
reverse_iterator rbegin()	It reference the last character of the string.
void reserve(inr len)	It requests a change in capacity.
allocator_type get_allocator();	It returns the allocated object associated with the string

 

Let us try some other types of examples using string

 Let us try to compare the elements

 

#include <iostream>  

#include <cstring>  

using namespace std;  

int main ()  

{  

  char key[] = "mango";  

  char buffer[50];  

  do {  

     cout<<"What is my favorite fruit? ";  

     cin>>buffer;  

  } while (strcmp (key,buffer) != 0);  

 cout<<"Answer is correct!!"<<endl;  

  return 0;  

}  

 

Output

 What is my favorite fruit? apple

What is my favorite fruit? banana

What is my favorite fruit? mango

The answer is correct!!

Let us try a concat example 

#include <iostream>  

#include <cstring>  

using namespace std;  

int main()  

{  

    char key[25], buffer[25];  

    cout << "Enter the key string: ";  

    cin.getline (key, 25);  

    cout << "Enter the buffer string: ";  

     cin.getline(buffer, 25);  

    strcat(key, buffer);   

    cout << "Key = " << key << endl;  

    cout << "Buffer = " << buffer<<endl;  

    return 0;  

}  

 

Output

 

Enter the key string: Welcome to

Enter the buffer string:  C++ Programming.

Key = Welcome to C++ Programming.

Buffer =  C++ Programming.

 

Let us try a string copy example

 

#include <iostream>  

#include <cstring>  

using namespace std;  

int main()  

{  

    char key[25], buffer[25];  

    cout << "Enter the key string: ";  

    cin.getline(key, 25);  

    strcpy(buffer, key);  

    cout << "Key = "<< key << endl;  

    cout << "Buffer = "<< buffer<<endl;  

    return 0;  

}  

Output:

Enter the key string: C++ Tutorial

Key = C++ Tutorial

Buffer = C++ Tutorial

 

Pointers and strings

Pointers in C++ are symbolic representations of addresses. They allow programs to simulate speech and to create and manipulate dynamic data structures. Using pointers, we get the first character of the string, which is the starting address of the string. As shown below, a given string can be accessed and printed using pointers.

 Let us try with a C++ program to print string using pointers

 #include <iostream>

using namespace std;

 

int main()

{

              string s = "Hello India";

 

              // pointer variable declared to store the starting

              // address of the string

              char* p = &s[0];

 

              // this loop will execute and print the character till

              // the character value is null this loop will execute and

              // print the characters

 

              while (*p != '\0') {

                             cout << *p;

                             p++;

              }

              cout << endl;

 

              return 0;

}

 Output 

 Hello India