C ++-矢量图 <class> 和std :: bad_alloc

Question

I am working on translating a program from matlab code to C++ where I have to use opencv libs on Linux (gcc version 4.9.2)

So I am trying to translate this line of matlab code:

repeatedMat = repmat(originalMat,[1 1 k]); 

and the last code I wrote is this:

void repeat(cv::Mat img, std::vector <cv::Mat> &output, uint32_t nx, uint32_t ny, uint32_t z)
{
    cv::Mat tmpMat = cv::repeat(img, nx, ny);
    output = std::vector <Mat> (z);

    for (uint32_t i = 0; i < output.size(); i++)
        output.insert(output.end(), tmpMat);
}

The problem is that I always run into std::bad_alloc error

terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc
Aborted

I don't know exactly why but I am thinking about some memory leak.. Is there a better (and working) way to do this ?

Answer 1

In C++, the condition of a for loop is evaluated in every iteration, so if you add a new element at the end of the vector, it grows by 1, so in the next iteration the counter i will not reach it. It should be something like:

for (uint32_t i = 0; i < z; i++)
    output.insert(output.end(), tmpMat);

But as rahnema1 said in the comments, you don't need to do that. You can create a vector with z copies of the same element without copy them:

output = std::vector <Mat> (z, tmpMat);

Also, because you have labelled your question as "c++11", let me another additional suggestions: return the vector by value, the compiler will avoid the copy.

std::vector <cv::Mat> repeat(cv::Mat img, uint32_t nx, uint32_t ny, uint32_t z)
{
    return std::vector<cv::Mat>(z, cv::repeat(img, nx, ny));
}