Different ways to access characters in a given String in C++

String class stores the characters as a sequence of bytes with the functionality of allowing access to the single-byte character. There are several ways to access substrings and individual characters of a string. The string class supports the following functions for this purpose:

1. operator[]
2. at()
3. substr()
4. find()
5. find_first_of()
6. find_last_of()

Let’s start discussing each of these methods in detail.

operator[]

operator[] returns the reference to the character at the position specified as the argument.

Syntax-

char& operator[](size_t pos);

Here, 
pos is the index of the character to be searched.

Below is the C++ program to implement the operator[] function-

C++

// C++ program to implement
// the operator[]
#include <iostream>
using namespace std;

// Driver code
int main()
{
    string str("GeeksforGeeks");
    cout << str[4];
    return 0;
}

Time Complexity : O(N)

Space Complexity : O(1)

Output

s

at()

at() function is used for accessing individual characters. With this function, character by character can be accessed from the given string.

Syntax-

char& string::at (size_type idx)

Below is the C++ to implement at()-

C++

// C++ program to implement
// at()
#include <iostream>
using namespace std;

// Driver code
int main()
{
    string s("GeeksForGeeks");
    cout << s.at(4);
    return 0;
}

Time Complexity : O(N)

Space Complexity : O(1)

Output

s

substr()

substr() function is used for retrieving a substring from a given string. This function takes two values start and len.

• string.h is the header file required for string functions.
• The starting index is 0.

Syntax-

string substr (size_type start, size_type len);

Here, 
start: Position of first character to be copied 
len: Length of the sub-string.

Below is the C++ program to implement the substr() function-

C++

// C++ program to implement
// the substr() function
#include <iostream>
using namespace std;

// Driver code
int main()
{
    string s("GeeksForGeeks");
    cout << s.substr(1, 5);

    return 0;
}

Output

eeksF

find()

find() function is used to find the first occurrence of a substring in the specified string being called upon.

• It returns the index of the first occurrence of the substring in the string.
• The default value of the starting position is 0.
• If the substring is not found then the function returns -1.

Syntax-

size_t find (const string& str, size_t pos = 0);

size_t find (const char* s, size_t pos = 0);

Here, 
str is the substring to be searched.
s is the C-style substring to be searched.
pos is the initial position from where to start string search. The default value is 0.

Below is the C++ program to implement the find() function-

C++

// C++ program to implement
// the find() function
#include <iostream>
using namespace std;

// Driver code
int main()
{
    string s("GeeksForGeeks");
    cout << s.find("For");

    return 0;
}

Output

5

Time Complexity : O(N)

Space Complexity : O(1)

find_first_of()

find_first_of() function is used to find the first character that matches any of the characters specified in the arguments. This function takes two arguments str and pos. 

Syntax-

size_t find_first_of (const string& str, size_t pos = 0) const;

Here, 
str is the string with characters to search for.
pos is the position of the first character in the string to be considered for search.

Below is the C++ program to implement find_first_of() function-

C++

// C++ program to implement
// the find_first_of() function
#include <iostream>
using namespace std;

// Driver code
int main()
{
    string s("GeeksForGeeks");
    cout << s.find_first_of('s');
    return 0;
}

Output

4

find_last_of()

find_last_of() function is used for finding the location of last occurrence of the specified characters from the given string.

Syntax-

find_last_of(char ch);

find_last_of(char ch, size_t position);

Here, 
ch is the character to be searched in the string.
position is the index till where the search is to be performed.

Below is the C++ program to implement find_last_of() function-

C++

// C++ program to implement
// the find_last_of() function
#include <iostream>
using namespace std;

// Driver code
int main()
{
    string s("GeeksForGeeks");
    cout << s.find_last_of('s');
    return 0;
}

Output

12