C++释放unsigned char指针出错

这代码为啥出错了
在网上看了各种教程
理论上不应该出错啊

windows 11 22H2,VS2022,ISOC++ 20

代码水平不高，请见谅

BigInt.h

#pragma once
#include <iostream>
#include <sstream>
#include <string>


class BigInt
{
    friend std::istream& operator>>(std::istream& in, BigInt& value);
    friend std::ostream& operator<<(std::ostream& out, const BigInt& value);

public:

    const static BigInt inf;
    const static BigInt ZERO;
    const static BigInt ONE;
    const static BigInt TWO;
    const static BigInt TEN;

public:

    BigInt();

    BigInt(const std::string& str);

    BigInt(const unsigned char* value, size_t length);

    BigInt(size_t length);

    BigInt(const BigInt& bigInt);

    ~BigInt();

    BigInt operator+(const BigInt& bigInt) const;


private:

    unsigned char* value;

    size_t length;

};

std::istream& operator>>(std::istream& in, BigInt& value);
std::ostream& operator<<(std::ostream& out, const BigInt& value);
std::string getTo(std::istream& in, int (*func)(int c));

BigInt.cpp

#include "BigInt.h"

const BigInt BigInt::inf = BigInt();
const BigInt BigInt::ZERO = BigInt("0");
const BigInt BigInt::ONE = BigInt("1");
const BigInt BigInt::TWO = BigInt("2");
const BigInt BigInt::TEN = BigInt("10");

BigInt::BigInt()
{
    this->length = 0;
    this->value = new unsigned char[this->length];
}

BigInt::BigInt(const std::string& str)
{
    this->length = str.length();
    this->value = new unsigned char[this->length];
    size_t i = 0L;
    for (size_t j = this->length - 1; i < this->length; i++, j--)
    {
        char c = str[j];
        if (c < '0' || c > '9')
        {
            break;
        }
        this->value[i] = c - '0';
    }
    for (; i < this->length; i++)
    {
        this->value[i] = 0;
    }
}

BigInt BigInt::operator+(const BigInt& bigInt) const
{
    size_t maxlen, minlen;
    if (bigInt.length < this->length)
    {
        minlen = bigInt.length;
        maxlen = this->length;
    }
    else
    {
        minlen = this->length;
        maxlen = bigInt.length;
    }

    BigInt out(maxlen);
    size_t i;
    for (i = 0; i < minlen; i++)
    {
        out.value[i] = this->value[i] + bigInt.value[i];
    }
    if (i < this->length)
    {
        for (; i < this->length; i++)
        {
            out.value[i] = this->value[i];
        }
    }
    if (i < bigInt.length)
    {
        for (; i < bigInt.length; i++)
        {
            out.value[i] = bigInt.value[i];
        }
    }

    // 这里还没写完

    return BigInt();
}

BigInt::BigInt(const unsigned char* value, const size_t len)
{
    this->length = len;
    this->value = new unsigned char[this->length];
    for (size_t i = 0L; i < this->length; i++)
    {
        this->value[i] = value[i];
    }
}

BigInt::BigInt(const size_t len)
{
    this->length = len;
    this->value = new unsigned char[this->length];
}

BigInt::BigInt(const BigInt& bigInt)
{
    this->length = bigInt.length;
    this->value = new unsigned char[this->length];
    for (size_t i = 0L; i < this->length; i++)
    {
        this->value[i] = bigInt.value[i];
    }
}

BigInt::~BigInt()
{
    if (this->value != nullptr)
    {
        delete[] this->value;
        this->value = nullptr;
    }
    this->length = 0;
}

std::istream& operator>>(std::istream& in, BigInt& value)
{
    char cbuf = '\n';
    while (isspace(in.peek())) cbuf = in.get();
    std::stringstream ss;
    ss << cbuf;
    while ((cbuf = in.peek()) != EOF)
    {
        if (cbuf < '0' || cbuf > '9')
        {
            break;
        }
        cbuf = in.get();
        ss << cbuf;
    }
    std::string str = ss.str();
    
    value = BigInt(str);
    return in;
}

std::ostream& operator<<(std::ostream& out, const BigInt& value)
{
    if (value.length == 0)
    {
        out << "inf";
        return out;
    }
    size_t i = value.length - 1;
    for (; value.value[i] == 0 && i > 0; i--);
    for (; i > 0; i--)
    {
        out << (char)(value.value[i] + '0');
    }
    out << (char)(value.value[i] + '0');

    return out;
}

std::string getTo(std::istream& in, int(*func)(int c))
{
    char cbuf = '\n';
    std::stringstream ss;
    while ((cbuf = in.peek()) != EOF)
    {
        if (func(cbuf))
        {
            break;
        }
        cbuf = in.get();
        ss << cbuf;
    }
    std::string str = ss.str();
    return str;
}

MathCalculator.cpp

#include "BigInt.h"
#include <iostream>
#include <iomanip>

using namespace std;

int main()
{
    while (true)
    {

        BigInt num1, num2, answer;
        string oper;

        cout << "> ";
        cin >> num1;

        oper = getTo(cin, isdigit);
        string::iterator end_pos = remove(oper.begin(), oper.end(), ' ');
        oper.erase(end_pos, oper.end());//移除空格

        cin >> num2;

        if (oper == "+")
        {
            // answer = num1 + num2;
        }
        else
        {
            cout << "没有这个符号【" << oper << "】" << endl;
            continue;
        }
        cout << num1 << ' ' << oper << ' ' << num2 << " = " << answer << endl;

        
    }

    return 0;
}

感谢，我忘了写operator=了
BigInt.h

BigInt& operator=(const BigInt& bigInt);

BigInt.cpp

BigInt& BigInt::operator=(const BigInt& bigInt)
{
    this->~BigInt();
    this->length = bigInt.length;
    this->value = new unsigned char[this->length];
    for (size_t i = 0L; i < this->length; i++)
    {
        this->value[i] = bigInt.value[i];
    }
    return *this;
}

operator>>里的 value = BigInt(str);这一句再研究哈。