Find index of a character in string in C++

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

1. Using `string::find`

The string::find member function returns the index of the first occurrence of the specified character in a string, or string::npos if the character is not found. The following example shows invocation of this function:

#include <iostream>

#include <string>

int main()

{

std::string s = "C++20";

char c = '+';

int index = s.find(c);

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

std::cout << "Character found at index " << index << std::endl;

} else {

std::cout << "Character not found" << std::endl;

}

return 0;

}

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Output:

Character found at index 1

Here’s an equivalent version using the std::find standard algorithm, which accepts a range to search for the specified element and returns an iterator to the first element in it.

#include <iostream>

#include <string>

#include <algorithm>

int main()

{

std::string s = "C++20";

char c = '+';

auto it = std::find(s.begin(), s.end(), '+');

if (it != s.end()) {

int index = std::distance(s.begin(), it);

std::cout << "Character found at index " << index << std::endl;

} else {

std::cout << "Character not found" << std::endl;

}

return 0;

}

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Output:

Character found at index 1

2. Using `std::string_view`

C++17 allows forming a string view of a character literal using std::literals::string_view_literals::operator""sv, declared in the header <string_view>. After getting the string view, we can use the find() function to get the position of the first character of the given character sequence, or std::string::npos if it is not found. For example,

#include <iostream>

#include <string_view>

using namespace std::string_view_literals;

int main()

{

size_t index = "C++20"sv.find('+');

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

std::cout << "Character found at index " << index << std::endl;

} else {

std::cout << "Character not found" << std::endl;

}

return 0;

}

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Output:

Character found at index 1

That’s all about finding the index of a character in a string in C++.

Find index of a character in string in C++

1. Using string::find

2. Using std::string_view

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1. Using `string::find`

2. Using `std::string_view`