将任意对象附加到数组有什么问题? [英] What is the problem with appending arbitrary object to the array?

问题描述

我有一个简单的程序，可以将文件中的字符串处理为任意类 Student(如下提供)并将其附加到自写容器 ArraySequence.当错误几乎总是发生在标记行(用 ***** 标记)时.

I have a simple program that process strings from a file into arbitrary class Student (provided below) and appends it to self-written container ArraySequence. When error almost always occurs on marked line (marked with *****).

班级学生:

class Student {
public:
    int year;
    std::string name;
    std::string surname;
    Student(int _year, std::string _name, std::string _surname) {
        this->year = _year;
        this->name = _name;
        this->surname = _surname;
    }
    Student(const Student& s) {
        this->year = s.year;
        this->name = s.name;
        this->surname = s.surname;
    }
    Student& operator=(const Student& s) {
        this->year = s.year;
        this->name = s.name;
        this->surname = s.surname;
        return *this;
    }
    bool operator==(const Student& s) const {
        if (this->year == s.year && this->name == s.name && this->surname == s.surname)
            return true;
        return false;
    }
};

主要:

int main() {
    std::ifstream data("filename");
    std::string buffer;
    ArraySequence<Student>* entities = new ArraySequence<Student>;

    getline(data, buffer, '\n');
    while (buffer.size() != 0) {
        std::cout << buffer << std::endl;
        int len = static_cast<int>(buffer.find(" "));
        std::string surname = buffer.substr(0, len);
        buffer = buffer.substr(len + 1);
        len = static_cast<int>(buffer.find(" "));
        std::string name = buffer.substr(0, len);
        int year = std::stoi(buffer.substr(len + 1));
        Student b(year, name, surname);
        entities->append(b); *****
        getline(data, buffer, '\n');
    }

    std::cout << count << std::endl;

附加:

template <typename T>
void ArraySequence<T>::append(const T& item) {
    ISequence<T>::length++;
    if (!(ISequence<T>::length - 1)) {
        data = (T*)malloc(sizeof(T));
    }
    else {
        data = (T*)realloc(data, sizeof(T) * ISequence<T>::length);
    }
    *(data + ISequence<T>::length - 1) = item;
}

错误:线程 1: EXC_BAD_ACCESS (code=EXC_I386_GPFLT);线程 1: EXC_BAD_ACCESS (code=1, address=0x3);

有时它会正常工作，但有时它会因错误而崩溃.

Sometimes it would just work, but other times it crashes with errors.

我使用的是 Xcode 11.1

I'm using Xcode 11.1

在线程 1 中，它说 c++ this->surname = s.surname;

In Thread 1 it says that problem with operator= of Student on the line c++ this->surname = s.surname;

遇到这种情况我该怎么办?有什么想法吗?

What can I do in a situation like this? Any ideas?

推荐答案

T 包含一个非平凡类型(Student 包含 std::string，加上非平凡的复制/赋值和析构函数)，使用 malloc 和 realloc 将无法正常工作.

T consists of a non-trivial type (Student contains std::string, plus non-trivial copy/ assignment and destructor), using malloc and realloc will not work correctly.

malloc 和 realloc 不会创建可行的对象.他们只分配内存.由于这些无效的 Student 对象，您的程序可能会崩溃.

malloc and realloc do not create viable objects. They only allocate memory. Your program likely crashes due to these invalid Student objects.

最简单的解决方案是重写ArraySequence::append 只使用new[] 和delete[]，而不是malloc 和 realloc.

The easiest solution is to rewrite ArraySequence<T>::append to only use new[] and delete[], not malloc and realloc.

注意:malloc 可以在使用 时使用place-new，但您没有为此目的使用 malloc.

Note: malloc can be used when using placement-new, but you were not using malloc for this purpose.

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