将嵌套std :: vector的元素复制到std :: vector

I have encountered problem in copying the element of nested std::vector to another std::vector.

我在将嵌套的std :: vector元素复制到另一个std :: vector时遇到了问题。

Example 1

例1

std::vector<std::vector<int>> foo;
std::vector<int> temp;
std::vector<int> goo;

temp.push_back(12345);
foo.push_back(temp);
goo = foo[0]; //error

Example 2

例2

temp.clear();
for(int i = 0; i<foo[0].size(); i++) {temp.push_back(foo[0][i])};
goo = temp; //error

Thus, can i know where is the problem and what should i do to copy the element of a nested vector to another vector??

因此，我可以知道问题在哪里，我应该怎么做才能将嵌套矢量的元素复制到另一个矢量？

EDIT: The actual scenario would be i have nested vector of cv::Point

编辑：实际情况是我有嵌套的cv :: Point矢量

std::vector<std::vector<cv::Point>> found_contour;

and would like to copy the element inside a std::vector<cv::Point> in a struct.

并希望在结构中复制std :: vector 中的元素。

struct Contours
{
    std::vector<cv::Point> contour;
    cv::RotatedRect minRect;
    cv::RotatedRect minEllipse;
}

Code Snippet:

代码片段：

cv::findContours(result,found_contour,found_hierachy,CV_RETR_TREE,CV_CHAIN_APPROX_SIMPLE,cv::Point(0,0));

std::vector<Contours> contour_struct;
contour_struct.reserve(found_contour.size());

for (size_t i = 0; i < found_contour.size(); i++)
{
    contour_struct[i].contour = found_contour[i];
    contour_struct[i].minRect = cv::minAreaRect(cv::Mat(found_contour[i]));
}

1 个解决方案

#1

cv::findContours(result,found_contour,found_hierachy,CV_RETR_TREE,CV_CHAIN_APPROX_SIMPLE,cv::Point(0,0));

std::vector<Contours> contour_struct;
contour_struct.reserve(found_contour.size()); //<-----problem

for (size_t i = 0; i < found_contour.size(); i++)
{
    contour_struct[i].contour = found_contour[i];
    contour_struct[i].minRect = cv::minAreaRect(cv::Mat(found_contour[i]));
}

vector::reserve only aquires space internally so that push_back does not run out of space. It does not actually add more objects into the vector. You can use this line instead:

vector :: reserve仅在内部获取空间，以便push_back不会耗尽空间。它实际上并没有在向量中添加更多对象。您可以使用此行代替：

contour_struct.resize(found_contour.size());

which will make sure that contour_struct is the right size.

这将确保contour_struct的大小合适。

#1

cv::findContours(result,found_contour,found_hierachy,CV_RETR_TREE,CV_CHAIN_APPROX_SIMPLE,cv::Point(0,0));

std::vector<Contours> contour_struct;
contour_struct.reserve(found_contour.size()); //<-----problem

for (size_t i = 0; i < found_contour.size(); i++)
{
    contour_struct[i].contour = found_contour[i];
    contour_struct[i].minRect = cv::minAreaRect(cv::Mat(found_contour[i]));
}