std::string::rfind in C++ with Examples

The std::string::rfind() function is a member of the std::string class defined in the <string> header. It searches a string in the reverse direction to locate the last occurrence of a character or substring.

• Supports searching for both characters and substrings.
• Returns the index of the match or std::string::npos if no match is found.

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

int main() {

    string str = "Welcome to GeeksforGeeks";

    cout << str.rfind('e');

    return 0;
}

21

Explanation: The last occurrence of 'e' is found at index 21, so rfind() returns 21.

Syntax

string_name.rfind(character); //Search for a character

string_name.rfind(substring); //Search for a substring

string_name.rfind(character, position); //Search before a given position

Parameters

The function accepts the following parameters:

• character - Character to search.
• substring - String to search.
• position (optional) - Position before which the search is performed.

Return Value

The function returns:

• Index of the last occurrence if found.
• std::string::npos if no match exists.

Complexity Analysis

where:

• n = length of source string
• m = length of substring

Searching for a single character is typically O(n).

Examples

The following examples demonstrate different uses of std::string::rfind().

1. Find the Last Occurrence of a Character

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

int main() {

    string str = "Welcome to GeeksforGeeks";

    size_t pos = str.rfind('e');

    if (pos != string::npos)
        cout << pos;

    return 0;
}

21

Explanation: rfind('e') searches from right to left and returns the index of the last 'e'.

2. Find the Last Occurrence of a Substring

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

int main() {

    string str = "Welcome to GeeksforGeeks";

    size_t pos = str.rfind("to");

    if (pos != string::npos)
        cout << pos;

    return 0;
}

8

Explanation: The substring "to" appears once, starting at index 8.

3. Search Before a Given Position

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

int main() {

    string str = "Welcome to GeeksforGeeks";

    size_t pos = str.rfind('e', 5);

    if (pos != string::npos)
        cout << pos;

    return 0;
}

1

Explanation: The search is restricted to characters before index 5, so the last matching 'e' is found at index 1.

4. Handling a Failed Search

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

int main() {

    string str = "Welcome to GeeksforGeeks";

    size_t pos = str.rfind("Java");

    if (pos == string::npos)
        cout << "Substring not found";

    return 0;
}

Substring not found

Explanation: Since "Java" does not exist in the string, rfind() returns string::npos.

Best Practices

Follow these practices while using std::string::rfind():

• Always compare the result with std::string::npos before using the returned index.
• Use the position parameter when searching within a specific portion of the string.
• Prefer rfind() over manual reverse traversal for better readability.
• Use find() instead if the first occurrence is required.

Comparison with Similar Functions