I can't double characters inside string with function

Question

I am trying to create a simple function that double the characters inside of a string and outputs the new string. Ex. "hello world" would become "hheelloo wwoorrl

Answer 1

Altough the solution by songyuanyao is nice, I think more C++ functions can be used...

#include 
#include 

// use string view, so a character array is also accepted
std::string DoubleChar(std::string_view const &str) noexcept {
    std::string newString;
    newString.reserve(str.size() * 2);
    for (auto character : str) { // use range based loop
        newString.append(2, character); // append the character twice
    }
    return newString;
}

#include 

int main() {
    std::string const str = "Hello world";

    std::cout << DoubleChar(str) << '\n';
}