Question

没有在这个问题上寻找答案，但是会有一些方向感激。我看过的每个地方和我尝试的所有答案都没有解决问题。

我有说明“动态地将变量分配给用户输入的内容。不能使用placeHolder变量（userInput [256}]）来捕获输入。将'\ 0'追加到结尾。”

我的原始代码是：

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;
}

我知道堆已损坏，我怀疑我正在改变分配的内存。我不确定为什么修复不起作用，所有教程都是这样。

Answer 1

以下是我认为您与your rubber duck的对话此时会如何：

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

你（跟你的橡皮鸭说话）：好的，所以上面归结为什么   是我为十个字符分配了一个缓冲区。 userInput在这里   指向十个字符userInput[0]到userInput[9]。

橡皮鸭：好的。

您：num和ptrLength都设置为值10。

橡皮鸭：对我有意义。

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

你：所以，我检查下一个字符是否是换行符，如果没有，我   将输入放在userInput[ptrLength]
中
Rubber Duck：等等，ptrLength的初始值是多少？

你：10，正如我刚才所说。
     橡皮鸭：但你不是只说你只有userInput[0]   通过userInput[9]，为你的缓冲区分配，并写作   此时userInput[10]的某些内容会破坏堆。

那么，你对这条橡皮鸭问题的答案是什么？

Answer 2

userInput[ptrLength]超出范围，userInput = new char[ptrLength];后不得访问。
条件ptrLength = num不是一个相等的测试，而是一个任务，我想这不是你想要的。
您在阅读后忘了更新ptrLength。
您删除了新分配的缓冲区并使其无法使用。
您应该删除通过new创建的内容。
您必须在分配delete之前使用nullptr 。同时使用delete[]表示通过new[]分配的内容。

在num = num*num;之后，num/2通常不会是之前的num。您必须计算平方根以从新num获取oid num。

更正后的代码：

#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; }

c ++动态内存分配导致堆损坏

2 个答案: