我无法使用功能将字符串内的字符加倍 [英] I can't double characters inside string with function

问题描述

我正在尝试创建一个简单的函数，该函数将字符串内的字符加倍并输出新的字符串.前任. "hello world"会变成"hheelloo wwoorrlldd"但是，使用我编写的函数，输出为空.如果有人能告诉我这是为什么，我将不胜感激.谢谢！

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 wwoorrlldd" However, with the function I wrote, the output is empty. If anyone can tell me why this is, I'd greatly appreciate it. Thank you!

using namespace std;
string doubleChar(string str) {
    string newString;
    for(int i =0;i<str.size();++i){
        newString[i] = str[i];
        newString[i+1] = str[i];
    }
    return newString;
}

推荐答案

尽管songyuanyao的解决方案很好，但我认为可以使用更多的C ++函数...

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

#include <string>
#include <string_view>

// 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 <iostream>

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

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

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