C++动态内存分配造成损坏的堆

Question

不寻找在这一个答案，但一些方向将不胜感激。我所看到的所有地方以及我尝试过的所有答案都不能解决问题。

我有指令声明“动态分配变量到用户输入的内容，不能使用placeHolder变量（userInput [256}]）来捕获输入。

我原来的代码是：

int main(){ 

    char cont = 'y'; 
    char *userInput = nullptr; 

    while (cont == 'y' || cont == 'Y') 
    { 

     int ptrLength = 0; 
     userInput = new char[ptrLength]; 

     cout << "Please enter a word or phrase: ";//2. Asks the user to enter any string (any sequence of characters) 
     while (cin.peek() != '\n'){ 
      cin >> userInput[ptrLength]; 
      ptrLength++; 
     } 
     //1. You must use a pointer to a C-string and dynamically allocate just enough memory to store all the characters entered by the user PLUS the ‘\0’ char than must be appended at the end of the C-string. 

     userInput[ptrLength] = '\0';   

     cout << endl; 
     myVowels(userInput, ptrLength); 
     cout << endl << endl; 
     //delete [] userInput; //deleting here breaks the program. Not sure why right now. 
     //userInput = nullptr; 
     //5. The user must be asked if he/she wants to continue entering values or quit. 
     cout << endl << "To enter another phrase press Y. To exit press any key." << endl; 
     cin >> cont; 
     cin.clear(); 
     cin.ignore(256, '\n'); 
    }//end while cont = Y 

    delete userInput; 
    userInput = nullptr; 
    system("pause"); 
    return 0; 
} 

更新的代码：

int main(){ 

    char cont = 'y'; 
    char *userInput = nullptr; 

    while (cont == 'y' || cont == 'Y') 
    { 

     int num = 10; 
     int ptrLength = num; 
     userInput = new char[ptrLength]; 
     char *temp = nullptr; 

     cout << "Please enter a word or phrase: ";//2. Asks the user to enter any string (any sequence of characters) 
//FIX I FOUND, BUT IT DOES NOT WORK AT ALL 
     while (cin.peek() != '\n'){ 
      cin >> userInput[ptrLength]; 
      if (ptrLength = num){ 
       num *= num; 
       temp = new char[num]; 
       for (int i = 0; i < num/2; i++) 
       { 
        temp[i] = userInput[i]; 
       } 
       delete [] userInput; 
       userInput = temp; 
       delete [] temp; 
      } 
     } 
     //1. You must use a pointer to a C-string and dynamically allocate just enough memory to store all the characters entered by the user PLUS the ‘\0’ char than must be appended at the end of the C-string. 

     userInput[ptrLength] = '\0';   

     cout << endl; 
     myVowels(userInput, ptrLength); 
     cout << endl << endl; 

     //userInput = nullptr; 
     //delete [] userInput; //This works, but by switching to nullptr I am not deleting the memory allocated. If I just have the delete with or without [] the program breaks. Tried with user input declared inside and outside of the WHILE statement. Heap is being corrupted. 

     //5. The user must be asked if he/she wants to continue entering values or quit. 
     cout << endl << "To enter another phrase press Y. To exit press any key." << endl; 
     cin >> cont; 
     cin.clear(); 
     cin.ignore(256, '\n'); 
    }//end while cont = Y 

    delete userInput; 
    userInput = nullptr; 
    system("pause"); 
    return 0; 
} 

我知道堆被损坏，我从我改变了分配内存的方式怀疑。我不确定为什么修复程序无法正常工作，所以这是所有的教程。

Answer 1

下面是我想象与your rubber duck您的通话将走在这一点上：

int num = 10; 
    int ptrLength = num; 
    userInput = new char[ptrLength]; 

你（说你的橡皮鸭子）：好了，上面有哪些归结为 的是，我被分配10个字符的缓冲区。 userInput这里 指向十个字符，userInput[0]到userInput[9]。

橡皮鸭：好的。

你说：这两个num和ptrLength被设置为10

橡胶鸭的价值：对我来说很有意义。

while (cin.peek() != '\n'){ 
     cin >> userInput[ptrLength]; 

您：那么，我是否读下一个字符是一个换行符，如果没有，我 放在userInput[ptrLength]

橡胶鸭输入：等等，什么是初始值ptrLength？

你：10，正如我刚才所说的那样。

橡胶鸭：但你不是刚说，你只有userInput[0] 通过userInput[9]，分配给您的缓冲区，并写入 东西userInput[10]，在这一点上，会破坏堆。

那么，你在这里对你的橡皮鸭的问题有什么回答？

Answer 2

• userInput[ptrLength]超出范围，不得在userInput = new char[ptrLength];之后访问。
• 条件ptrLength = num不是一个平等测试，但一个任务，我想这不是你想要的。
• 您忘了在阅读后更新ptrLength。
• 您删除了新分配的缓冲区，并使其不可用。
• 您应该删除通过new创建的任何内容。
• 必须使用delete之前 assgning nullptr。对于通过new[]分配的内容，还可以使用delete[]。
• 经过num = num*num;,num/2一般不会在先num。你必须计算平方根，从新的num获得oid num。

校正代码：

#include <iostream> 
#include <cstdlib> 
using std::cout; 
using std::cin; 
using std::endl; 

void myVowels(const char *userInput, int ptrLength){ 
    cout << "myVowels(" << userInput << ", " << ptrLength << ")\n"; 
} 

int main(){ 

    char cont = 'y'; 
    char *userInput = nullptr; 

    while (cont == 'y' || cont == 'Y') 
    { 

     int num = 10; 
     int ptrLength = 0; 
     userInput = new char[num]; 
     char *temp = nullptr; 

     cout << "Please enter a word or phrase: ";//2. Asks the user to enter any string (any sequence of characters) 
     while (cin.peek() != '\n'){ 
      cin >> userInput[ptrLength++]; 
      if (ptrLength == num){ 
       int oldNum = num; 
       num *= num; 
       temp = new char[num]; 
       for (int i = 0; i < oldNum; i++) 
       { 
        temp[i] = userInput[i]; 
       } 
       delete [] userInput; 
       userInput = temp; 
      } 
     } 
     //1. You must use a pointer to a C-string and dynamically allocate just enough memory 
     // to store all the characters entered by the user PLUS the ‘\0’ char than must be 
     // appended at the end of the C-string. 

     userInput[ptrLength] = '\0'; 

     cout << endl; 
     myVowels(userInput, ptrLength); 
     cout << endl << endl; 

     delete [] userInput; 
     userInput = nullptr; 

     //5. The user must be asked if he/she wants to continue entering values or quit. 
     cout << endl << "To enter another phrase press Y. To exit press any key." << endl; 
     cin >> cont; 
     cin.clear(); 
     cin.ignore(256, '\n'); 
    }//end while cont = Y 

    system("pause"); 
    return 0; 
}