Strings in C++

C++ strings are sequences of characters stored in a char array. Strings are used to store words and text. They are also used to store data, such as numbers and other types of information. Strings in C++ can be defined either using the std::string class or the C-style character arrays.

1. C Style Strings

These strings are stored as the plain old array of characters terminated by a null character ‘\0’. They are the type of strings that C++ inherited from C language.

Syntax:

char str[] = "GeeksforGeeks";

Example:

C++

// C++ Program to demonstrate strings
#include <iostream>
using namespace std;

int main()
{

    char s[] = "GeeksforGeeks";
    cout << s << endl;
    return 0;
}

Output

GeeksforGeeks

2. std::string Class

These are the new types of strings that are introduced in C++ as std::string class defined inside <string> header file. This provides many advantages over conventional C-style strings such as dynamic size, member functions, etc.

Syntax:

std::string str("GeeksforGeeks");

Example:

C++

// C++ program to create std::string objects
#include <iostream>
using namespace std;

int main()
{

    string str("GeeksforGeeks");
    cout << str;
    return 0;
}

Output

GeeksforGeeks

One more way we can make strings that have the same character repeating again and again.

Syntax:

std::string str(number,character);

Example:

C++

#include <iostream>
using namespace std;

int main()
{
    string str(5, 'g');
    cout << str;
    return 0;
}

Output:

ggggg

Ways to Define a String in C++

Strings can be defined in several ways in C++. Strings can be accessed from the standard library using the string class. Character arrays can also be used to define strings. String provides a rich set of features, such as searching and manipulating, which are commonly used methods. Despite being less advanced than the string class, this method is still widely used, as it is more efficient and easier to use. Ways to define a string in C++ are:

• Using String keyword
• Using C-style strings

1. Using string Keyword

It is more convenient to define a string with the string keyword instead of using the array keyword because it is easy to write and understand.

Syntax:

string s = "GeeksforGeeks";
string s("GeeksforGeeks");

Example:

C++

// C++ Program to demonstrate use of string keyword
#include <iostream>
using namespace std;

int main()
{

    string s = "GeeksforGeeks";
    string str("GeeksforGeeks");

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

    return 0;
}

Output

s = GeeksforGeeks
str = GeeksforGeeks

2. Using C-style strings

Using C-style string libraries 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[] = {'g', 'f', 'g', '\0'};
char s[4] = {'g', 'f', 'g', '\0'};
char s[4] = "gfg";
char s[] = "gfg";

Example:

C++

// C++ Program to demonstrate C-style string declaration
#include <iostream>
using namespace std;

int main()
{

    char s1[] = { 'g', 'f', 'g', '\0' };
    char s2[4] = { 'g', 'f', 'g', '\0' };
    char s3[4] = "gfg";
    char s4[] = "gfg";

    cout << "s1 = " << s1 << endl;
    cout << "s2 = " << s2 << endl;
    cout << "s3 = " << s3 << endl;
    cout << "s4 = " << s4 << endl;

    return 0;
}

Output

s1 = gfg
s2 = gfg
s3 = gfg
s4 = gfg

Another example of C-style string:

C++

#include <iostream>
using namespace std;

int main()
{
    string S = "Geeeks for Geeks";
    cout << "Your string is= ";
    cout << S << endl;

    return 0;
}

Output

Your string is= Geeeks for Geeks

How to Take String Input in C++

String input means accepting a string from a user. In C++. We have different types of taking input from the user which depend on the string. The most common way is to take input with cin keyword with the extraction operator (>>) in C++. Methods to take a string as input are:

• cin
• getline
• stringstream

1. Using Cin

The simplest way to take string input is to use the cin command along with the stream extraction operator (>>). 

Syntax:

cin>>s;

Example:

C++

// C++ Program to demonstrate string input using cin
#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
String is: 

Output:

Enter String
GeeksforGeeks
String is: GeeksforGeeks

2. Using getline 

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

Syntax:

getline(cin,s);

Example:

C++

// C++ Program to demonstrate use of getline function
#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 String
String is: 

Output:

Enter String
GeeksforGeeks
String is: GeeksforGeeks

3. Using stringstream

The stringstream class in C++ is used to take multiple strings as input at once. 

Syntax:

stringstream stringstream_object(string_name);

Example:

C++

// C++ Program to demonstrate use of stringstream object
#include <iostream>
#include <sstream>
#include<string>

using namespace std;

int main()
{

    string s = " GeeksforGeeks to the Moon ";
    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

GeeksforGeeks
to
the
Moon

How to Pass Strings to Functions?

In the same way that we pass an array to a function, strings in C++ can be passed to functions as character arrays. Here is an example program:

Example:

C++

// C++ Program to print string using function
#include <iostream>
using namespace std;

void print_string(string s)
{
    cout << "Passed String is: " << s << endl;
    return;
}

int main()
{

    string s = "GeeksforGeeks";
    print_string(s);

    return 0;
}

Output

Passed String is: GeeksforGeeks

Pointers and Strings

Pointers in C++ are symbolic representations of addresses. They enable programs to simulate call-by-reference as well as to create and manipulate dynamic data structures. By using pointers we can get the first character of the string, which is the starting address of the string. As shown below, the given string can be accessed and printed through the pointers.

Example:

C++

// C++ Program to print string using pointers
#include <iostream>
using namespace std;

int main()
{

    string s = "Geeksforgeeks";

    // 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

Geeksforgeeks

Difference between String and Character array in C++

The main difference between a string and a character array is that strings are immutable, while character arrays are not.

String	Character Array
Strings define objects that can be represented as string streams.	The null character terminates a character array of characters.
No Array decay occurs in strings as strings are represented as objects.	The threat of array decay is present in the case of the character array
A string class provides numerous functions for manipulating strings.	Character arrays do not offer inbuilt functions to manipulate strings.
Memory is allocated dynamically.	The size of the character array has to be allocated statically.

Know more about the difference between strings and character arrays in C++

C++ String Functions

C++ provides some inbuilt functions which are used for string manipulation, such as the strcpy() and strcat() functions for copying and concatenating strings. Some of them are:

Function	Description
length()	This function returns the length of the string.
swap()	This function is used to swap the values of 2 strings.
size()	Used to find the size of string
resize()	This function is used to resize the length of the string up to the given number of characters.
find()	Used to find the string which is passed in parameters
push_back()	This function is used to push the passed character at the end of the string
pop_back()	This function is used to pop the last character from the string
clear()	This function is used to remove all the elements of the string.
strncmp()	This function compares at most the first num bytes of both passed strings.
strncpy()	This function is similar to strcpy() function, except that at most n bytes of src are copied
strrchr()	This function locates the last occurrence of a character in the string.
strcat()	This function appends a copy of the source string to the end of the destination string
find()	This function is used to search for a certain substring inside a string and returns the position of the first character of the substring.
replace()	This function is used to replace each element in the range [first, last) that is equal to old value with new value.
substr()	This function is used to create a substring from a given string.
compare()	This function is used to compare two strings and returns the result in the form of an integer.
erase()	This function is used to remove a certain part of a string.

C++ Strings iterator functions 

In C++ inbuilt string iterator functions provide the programmer with an easy way to modify and traverse string elements. These functions are:

Functions	Description
begin()	This function returns an iterator pointing to the beginning of the string.
end()	This function returns an iterator that points to the end of the string.
rfind()	This function is used to find the string’s last occurrence.
rbegin()	This function returns a reverse iterator pointing to the end of the string.
rend()	This function returns a reverse iterator pointing to the beginning of the string.
cbegin()	This function returns a const_iterator pointing to the beginning of the string.
cend()	This function returns a const_iterator pointing to the end of the string.
crbegin()	This function returns a const_reverse_iterator pointing to the end of the string.
crend()	This function returns a const_reverse_iterator pointing to the beginning of the string.

Example:

C++

// C++ Program to demonstrate string iterator functions
#include <iostream>
using namespace std;

int main()
{
    // declaring an iterator
    string::iterator itr;

    // declaring a reverse iterator
    string::reverse_iterator rit;

    string s = "GeeksforGeeks";

    itr = s.begin();

    cout << "Pointing to the start of the string: " << *itr<< endl;

    itr = s.end() - 1;

    cout << "Pointing to the end of the string: " << *itr << endl;

    rit = s.rbegin();
    cout << "Pointing to the last character of the string: " << *rit << endl;

    rit = s.rend() - 1;
    cout << "Pointing to the first character of the string: " << *rit << endl;

    return 0;
}

Output

Pointing to the start of the string: G
Pointing to the end of the string: s
Pointing to the last character of the string: s
Pointing to the first character of the string: G

String Capacity Functions

In C++, string capacity functions are used to manage string size and capacity. Primary functions of capacity include:

Function	Description
length()	This function is used to return the size of the string
capacity()	This function returns the capacity which is allocated to the string by the compiler
resize()	This function allows us to increase or decrease the string size
shrink_to_fit()	This function decreases the capacity and makes it equal to the minimum.

Example:

C++

#include <iostream>
using namespace std;

int main()
{

    string s = "GeeksforGeeks";

      // length function is used to print the length of the string
    cout << "The length of the string is " << s.length() << endl;

      // capacity function is used to print the capacity of the string
    cout << "The capacity of string is " << s.capacity()<< endl;

    // the string.resize() function is used to resize the string to 10 characters
      s.resize(10);

    cout << "The string after using resize function is " << s << endl;

      s.resize(20);

    cout << "The capacity of string before using shrink_to_fit function is "<< s.capacity() << endl;

      // shrink to fit function is used to reduce the capacity of the container
    s.shrink_to_fit();

    cout << "The capacity of string after using shrink_to_fit function is "<< s.capacity() << endl;

    return 0;
}

Output

The length of the string is 13
The capacity of string is 15
The string after using resize function is GeeksforGe
The capacity of string before using shrink_to_fit function is 30
The capacity of string...

In conclusion, this article explains how strings can be defied in C++ using character arrays and string classes. The string class provides more advanced features, while the character array provides basic features but is efficient and easy to use. In this article, we also discussed the various methods to take input from the user.

To know more about std::string class, refer to the article – std::string class in C++