Find index of last occurrence of a char in a C++ string

This post will discuss how to find the index of the last occurrence of a char in a C++ string.

1. Using `string::rfind`

The standard approach to find the index of the last occurrence of a char in a string is using the string::rfind member function. If the character doesn’t occur in the string, the function returns string::npos.

#include <iostream>

#include <string>

#include <algorithm>

int main()

{

std::string str = "A,B,C";

char ch = ',';

size_t index = str.rfind(ch);

if (index != std::string::npos) {

std::cout << index << std::endl; // 3

}

return 0;

}

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2. Using `std::find`

Alternatively, we can use the std::find algorithm with a reverse iterator and then use the std::distance (or pointer arithmetic) to get the index of the last occurrence.

#include <iostream>

#include <string>

#include <algorithm>

#include <iterator>

int main()

{

std::string str = "A,B,C";

char ch = ',';

auto it = std::find(str.rbegin(), str.rend(), ch);

std::cout << std::distance(str.begin(), (it + 1).base()) << std::endl; // 3

return 0;

}

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3. Using Loop

Finally, we can iterate over the string in reverse order and find the index of the first matching character. This can be done using a regular for-loop, as shown below:

#include <iostream>

#include <string>

#include <algorithm>

int main()

{

std::string str = "A,B,C";

char ch = ',';

int index = -1;

for (int i = str.size() - 1; i >=0; i--) {

if (str[i] == ch) {

index = i;

break;

}

std::cout << index << std::endl; // 3

return 0;

}

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That’s all about finding the index of the last occurrence of a char in a C++ string.

Find index of last occurrence of a char in a C++ string

1. Using string::rfind

2. Using std::find

3. Using Loop

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1. Using `string::rfind`

2. Using `std::find`