随机密码生成器的 C++ 循环错误“以非零状态退出”

Question

所以我正在尝试学习 C++ 中的循环和条件，所以我决定编写一个程序，为用户生成一个随机密码。出于某种原因，代码可能工作了 1/5 次，但其余时间它只是给了我“以非零状态退出”。 谢谢， 埃文

#include <iostream>
#include <cstdlib>
#include <chrono>
#include <thread>
#include <time.h>
using namespace std;
int main() 
{
    using namespace std::this_thread;
    using namespace std::chrono;
//  Vars
    string lett;
    int input;
    string password("");
    string lettArray [] = {"a", "b", "c", "d", "e","f", "g", "h", "i", "j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"};

//  Prompt
    cout << "How long would you like your password to be?";
    cin >> input;
//  Loop
    for(int i = 0; i < input; i++)
    {
        struct timespec ts;
        clock_gettime(CLOCK_MONOTONIC, &ts);
        srand((time_t)ts.tv_nsec);
        int random = (rand() % 26 + 1);
        lett = lettArray[random];
        password = password + lett;
        sleep_for(milliseconds(10));
        cout << "." << endl;
        if (random == 0 )
            break;
    }
//  Output
    cout << password << endl;
    return 0;
}

Answer 1

这个程序随机失败的原因（双关语）是你使用了 C 数组，而你的索引范围错误。

C 数组，例如 lettArray，不检查是否违反了数组边界。在您的示例中，如果您运行此程序，lettArray[26] 会给您一个分段错误，因为该内存地址中没有string 元素。 C 数组不检查边界，因此很难知道出了什么问题。这在复杂的程序中可能会变得特别棘手，因为如果该内存地址中发生了某些事情，您可能会得到一个荒谬的结果。

更好的实现是使用std::vector:

#include <iostream>
#include <cstdlib>
#include <chrono>
#include <thread>
#include <time.h>
#include <vector>
using namespace std;
int main() 
{
    // You don't need these two lines
    //using namespace std::this_thread;
    //using namespace std::chrono;

    //  Vars
    string lett;
    int input;
    string password("");

    // Vector index range: 0-25
    vector<string> lettArray = {"a", "b", "c", "d", "e","f", "g", "h", "i", "j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"};

    // You only need to initialise the seed once.
    struct timespec ts;
    clock_gettime(CLOCK_MONOTONIC, &ts);
    srand((time_t)ts.tv_nsec);

//  Prompt
    cout << "How long would you like your password to be?";
    cin >> input;

//  Loop
    for(int i = 0; i < input; i++)
    {
        int random = (rand() % 26 ); // You get results between 0-25
        // Using lettArray.at(26) will result in a crash with a clear 
        // message that bounds are violated  
        lett = lettArray.at(random); 
        password = password + lett;
        cout << "." << endl;

       // Don't see a reason for this if statement
       // if (random == 0 ){
       //     continue;
       //}
    }
//  Output
    cout << password << endl;
    return 0;
}

我还将随机种子移到循环之外（您只需要一次），也没有理由暂停 10 毫秒。无论如何，您都会看到您的结果是正确随机的。