运算符重载实现:0xC0000005:读取位置存在访问冲突

当在我的BigInt实现中执行return BigInt(*this) += other;时，会抛出错误0xC0000005: Access violation reading location (insert memory location here)，并关闭程序。它为什么这么做有什么帮助吗？对于我的程序的上一个上下文，请转到复制构造函数问题C++："；0xC0000005：访问违规写入位置0x00000000；

BigInt.cpp

// binary addition
BigInt BigInt::operator+(BigInt const& other) const {
    return BigInt(*this) += other;
}
// compound addition-assignment operator
BigInt BigInt::operator+=(BigInt const& other) {
    //return this->data = this->data + other.data;
    //BigInt thisBigInt = *this;
    if (!other.isPositive) {
        //return thisBigInt -= other;
    }
    //possible check for both negative???

    int sum = 0; //holds the sum of the value in both vectors
    int maxSize = 0; //holds size of biggest BigInt
    int carry = 0; //holds carry over value
    int sizeDifference = 0; //holds size difference between b and a if b is bigger
    //check size
    while (bigIntVector->getSize() < other.bigIntVector->getSize()) {
        bigIntVector->resize(); //increase size of first big int until it matches size of second
    }
    if (bigIntVector->getSize() > other.bigIntVector->getSize()) {
        sizeDifference = bigIntVector->getSize() - other.bigIntVector->getSize();
        //cout << "sizeDiff: " << sizeDifference << endl;
    }
    maxSize = bigIntVector->getSize();
    int otherCounter = other.bigIntVector->getSize() - 1; //keeps track if we are done getting digits from other array
    //cout << "otherCounter: " << otherCounter << endl;
    for (int i = maxSize - 1; i >= 0; i--) {
        //cout << "element1: " << bigIntVector.getElementAt(i) << endl;
        //cout << "element2: " << other.bigIntVector.getElementAt(i) << endl;
        sum += bigIntVector->getElementAt(i);
        if (otherCounter >= 0) {
            sum += other.bigIntVector->getElementAt(i - sizeDifference); //move index if size is different
            sum += carry;
            carry = 0;
            //cout << "sum: " << sum << endl;
            if (sum > 9) {
                ++carry;
                bigIntVector->setElementAt(i, sum%base);
            }
            else {
                carry = 0;
                bigIntVector->setElementAt(i, sum%base);
            }
            --otherCounter; //only decrement otherCounter if we have reached 2nd vector elements
        }
        if (otherCounter < 0 && carry > 0) {
            bigIntVector->resize(); //increase size of big int
            bigIntVector->setElementAt(i, carry); //set carry in front of sum spot
        }
        sum = 0;
    }
    return *this;
}