问题描述
我在写一个打开Matlab API引擎的c ++代码。在演示文件Matlab_ROOT / extern / examples / eng_mat / engdemo.cpp中，它显示了如何将一个简单的1d c样式数组复制到mxArray：
I'm writing a c++ code that opens Matlab API engine. In the demo file Matlab_ROOT/extern/examples/eng_mat/engdemo.cpp, it shows how to copy a simple 1d c style array to a mxArray:
mxArray *T = NULL; double time[10] = {};
T = mxCreateDoubleMatrix( 1,10,mxREAL);
memcpy((void*)mxGetPr(T), (void*)time, sizeof(time));
我可以理解这段代码;因此1d mxArray 对象用线性存储元素。
I can understand this code; so a 1d mxArray object stores the elements linearly.
但是，假设我有一个2d（或更多）的c数组，并且 mxArray >
However, suppose I have a 2d (or more) c array and mxArray of same size:
double time[3][5];
mxArray *T;
T = mxCreateDoubleMatrix(3,5,mxREAL);
，我想将c数组时间的元素复制到 mxArray T 。我如何做到这一点？我想如果我使用 memcpy ，它将取决于元素存储在 mxArray 对象的顺序。非常感谢！
and I want to copy the elements of the c array time into mxArray T. How can I do this? I suppose if I use memcpy, it would depend on the sequence of element storage in mxArray objects. Thanks!
推荐答案
无论你的 mxArray 将其作为连续块存储在存储器中（列第一顺序）。也就是说，如果你的矩阵 M 是2乘3
No matter what the dimensionality of your mxArray matlab always stores it as a continuous chunk in memory (column first order). That is, if your matrix M is 2-by-3
M = [ 11, 12, 13;
21, 22, 23 ];
在内存中，Matlab将其存储为
In memory, Matlab stores it as
[11, 21, 12, 22, 13, 23]
（如果您 M（：）），您会得到相同的顺序。
(The same order you'll get if you do M(:)).
将 double [3] [5] 转换为 mxArray ，您必须发出 > memcpy 命令：
Therefore, to convert a double[3][5] to mxArray you'll have to issue several memcpy commands:
double* ptr = mxGetPr( T );
for ( int i=0; i<3; i++ )
memcpy( (void*)(ptr+i*5), (void*)time[i], 5*sizeof(double) );
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