Get matrix size from a pointer- MEX

Question

Masoud 2015-8-24

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/235554-get-matrix-size-from-a-pointer-mex

回答： Walter Roberson 2015-8-24

Hello folks,

I read the second variable in C++

#define D prhs[1]
double** *d = mxGetPr(D);  // get the pointer

Now I want to get the size of D

int mySize = mxGetM(D);

cool...Now how can I get the size from the pointer d (not D)?

int mySize = mxGetM((const mxArray) d); // does not work

Thanks,

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2015-8-24

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/235554-get-matrix-size-from-a-pointer-mex#answer_190152

在 MATLAB Online 中打开

You cannot do that. MATLAB can store multiple arrays as pointing to the same data, as long as all of the arrays have the same total number of elements. There is no one "size" for a data block.

P = rand(52,5);
Q = reshape(P, 13, 5, 4);

P and Q will have the same data pointer. R = reshape(Q, 13, 4, 5) would have the same data pointer too and probably makes more sense, but reshape() does not care about whether the reshape makes sense, only that the number of elements remains constant.