opencv Mat矩阵元素的访问问题

Question

double SAD = 0;
Mat temp;
temp = l - r;
cout << "temp=" << endl;
cout << temp << endl;
//Mat t;
temp = abs(temp);
cout << "temp=" << endl;
cout << temp << endl;
for (int i = 0;i < temp.rows;i++)
{
uchar *t = temp.ptr(i);
for (int j=0;j < temp.cols;j++)
{
SAD = SAD + t[j];///////////这里这里这里
}
}
return SAD;
为啥我这样访问矩阵元素没成功，我的SAD没得到temp矩阵里面的元素累加和？我已经检验过我的temp矩阵，里面有值
还有：
int SAD = 0;
Mat temp;
temp = l - r;
cout << "temp=" << endl;
cout << temp << endl;
//Mat t;
temp = abs(temp);
cout << "temp=" << endl;
cout << temp << endl;
for (int i = 0;i < temp.rows;i++)
{
//uchar *t = temp.ptr(i);
for (int j=0;j < temp.cols;j++)
{
SAD = SAD + temp.at(i, j);////中断中断中断
}
}
return SAD;
我用at函数会中断是怎么回事

Answer 1

http://blog.csdn.net/frogjason/article/details/8567867