Question

我想从c ++代码返回一个Mat对象到Unity。但是，我在c ++部分得到访问冲突错误

Unity Editor [version: Unity 2017.3.0f3_a9f86dcd79df]

SaliencyCV.dll caused an Access Violation (0xc0000005)
in module SaliencyCV.dll at 0033:270027f0.

Error occurred at 2018-03-06_235212.
C:\Program Files\Unity\Editor\Unity.exe, run by Dilara.
43% memory in use.
16266 MB physical memory [9199 MB free].
18698 MB paging file [9861 MB free].
134217728 MB user address space [134185466 MB free].
Read from location 990d0000 caused an access violation.

这是c ++代码：

uchar* cppMethod(uchar* frameData, int WIDTH, int HEIGHT, int* rows, int* cols)
{
    Mat img(HEIGHT, WIDTH, CV_8UC3);
    img.data = frameData;

    flip(img, img, 0);

    Mat result = calculateSaliency(img);

    *rows = result.rows;
    *cols = result.cols;

    int length = result.rows * result.cols * 3;

    uchar* tmpArr = result.data;

    uchar* resultArray = new uchar[length];

    for (int i = 0; i < length; i++)
    {
        resultArray[i] = tmpArr[i]; 
    }

    return resultArray;
}

有人可以帮助我吗？

Answer 1

您应该调用正确的Mat构造函数which accepts external data pointer，以使对象不释放/破坏相应的内存位置data指向。您可以在Mat::release()中了解此行为。

您的代码存在的问题是

Mat img(HEIGHT, WIDTH, CV_8UC3)分配一个大小为CV_8UC3的{{1}}内存块，但未使用（因为您要将HEIGHT*WIDTH成员变量更改为指向不同的内存位置，反正），
在功能退出时，data被销毁，从而导致对img的调用，而release()则会导致frameData，预期的行为

将前两行更改为

Mat img(HEIGHT, WIDTH, CV_8UC3, frameData);

如果您将resultArray传递给C＃，那么您很可能不管理指向内存的生命周期，那么您很可能会发生内存泄漏。 @Programmer在回答你之前的问题时已经建议你应该在C＃中分配内存，将它传递给C ++，并在C ++端就地编写。

简而言之，你应该有类似的东西：

#include <algorithm>

void cppMethod(uchar *frameData, uchar *out, const int WIDTH, const int HEIGHT,
               int *rows, int *cols) {
  /* this constructor will not manage frameData's lifetime */
  Mat img(HEIGHT, WIDTH, CV_8UC3, frameData);

  /* in-place operation */
  flip(img, img, 0);

  /* local variable --- it will be destructed properly */
  Mat result = calculateSaliency(img);

  /* well-defined if rows and cols are scalars passed by reference */
  *rows = result.rows;
  *cols = result.cols;

  /* make sure length will not overflow */
  int length = result.rows * result.cols * 3;

  /* you don't need this */
  // uchar *tmpArr = result.data;

  /* you sholuld NOT do this */
  // uchar *resultArray = new uchar[length];

  // use std::copy from <algorithm>
  // for (int i = 0; i < length; i++) {
  //   resultArray[i] = tmpArr[i];
  // }

  std::copy(result.data, result.data + length, out);

  // return resultArray;
}

将Mat对象C ++传递给Unity

1 个答案: