Segmentation fault - trying to pass matlab code to c ++ - c++

Question

I'm trying to pass a code that is in matlab for c ++ but it is giving segmentation fault (core dumped), can someone help me please?
Code in MATLAB
function strip = strips(strip,n,number_pixel)
se = strel('square', 3);
strip=imdilate(strip, se);
strip = imfill(strip);
[m1,n1] = size(strip);
vet=0;
for j=1:n1
for i=1:m1
if strip(i,j)==0
vet=vet+1;
end
end
aux(j)=vet;
vet=0;
end
limite=uint8(number_pixel/4);
for i=1:n1
if aux(i) < limite
strip(:, i)=1;
end
if aux(i) >= limite
strip(:, i)=0;
end
end
end
Code in C++
Mat strips(Mat strip, int n, int number_pixel){
int vet = 0;
int limite = (number_pixel/4);
int v[strip.cols];
dilate(strip, strip, getStructuringElement(MORPH_ELLIPSE, Size(3,3)));
strip = imfill(strip);
int n1 = strip.cols;
int m1 = strip.rows;
for (int j = 0; j < n1; j++){
for (int i = 0; i < m1; i++){
if(strip.at<uchar>(i, j) == 0){
vet += 1;
}
}
v[j] = vet;
vet = 0;
}
for (int i = 0; i < n1; i++){
int j;
if (v[i] < limite){
strip.at<uchar>(i, j) = 1;
}
if (v[i] >= limite){
strip.at<uchar>(i, j) = 0;
}
}
}
I already implemented the functions as imfill, I think my error is in the loop, but I can't find

Answer 1

It is very hard to tell what the problem is, when not having a fully working example. One obvious problem with your code is, that you use j uninitialized in your second loop:
for (int i = 0; i < n1; i++){
int j;
if (v[i] < limite){
strip.at<uchar>(i, j) = 1; // <- uninitialized j is used
}
//...
}
This is undefined behavior and basically everything could happen. j allocates memory but does not have a specific value. See this answer:
Local variables get their initial values from whatever random data is in the stack space they occupy at that moment.
That is j could be a very large integer and you try to access a value out of bounds. Or using j itself causes the error. As I said, the behavior is undefined.
EDIT I also think the second part of your code should be changed. strip(:,i)=1 sets the ith column of the 2D array to 1. Assuming that strip.at<uchar>(i, j) returns only a reference to a single value, your c++ code should be something like this:
for (int i = 0; i < n1; i++){
if (v[i] < limite){
// go through all rows and set the i-th column to 1.
for (int j = 0; j < m1; ++j)
strip.at<uchar>(j, i) = 1;
}
//...
}