我有以下c ++向量:
std::vector<myStruct> myVec;
其中myStruct包含:
struct myStruct {
Point3D start;
Point3D end;
double lenght;
}
struct Point3D {
double x, y, z;
}
现在在我的mex文件中,我想将其转换为mxArray,同时保持相同的结构。
当前(无效)代码:
// basic 'out'
mxArray *out;
mwSize dims[2] = { 1, 1 };
const char *pointField[] = {"point"};
const char *fields[] = {"start", "end","lenght"};
const char *3dFields[] = {"x", "y", "z"};
out = mxCreateStructArray(2,dims,(int)myVec.size(),pointField);
for( int i = 0 ; i < myVec.size() ; ++i)
{
// create struct to fill
mxArray *point = mxCreateStructArray(2, dims, 3, fields);
// create struct for start
mxArray *start= mxCreateStructArray(2, dims, 3, 3dFields);
mxSetField( start, 0, "x", mxCreateDoubleScalar(myVec[i].start.x) );
mxSetField( start, 0, "y", mxCreateDoubleScalar(myVec[i].start.y) );
mxSetField( start, 0, "z", mxCreateDoubleScalar(myVec[i].start.z) );
// create struct for end
mxArray *end= mxCreateStructArray(2, dims, 3, 3dFields);
mxSetField( end, 0, "x", mxCreateDoubleScalar(myVec[i].end.x) );
mxSetField( end, 0, "y", mxCreateDoubleScalar(myVec[i].end.y) );
mxSetField( end, 0, "z", mxCreateDoubleScalar(myVec[i].end.z) );
// add start + end to 'point'
mxSetField( point, 0, "start", start);
mxSetField( point, 0, "end", end);
mxSetField( point, 0, "lenght", mxCreateDoubleScalar(myVec[i].lenght) );
// add completed 'point' struct to out at given index i
mxSetField(out, i, "point", point );
}
plhs[0] = out;
如您所见,拥有1个输出值非常重要,该输出值可以包含多个“点”-结构,每个点都有一个start(xyz)-struct,end(xyz)-struct和lenght值。
到目前为止,该代码仅以正确的格式输出1个单一结构,但是对于第二次迭代,它仅在“ point”所在的级别直接创建一个空的“ end”值。
我必须更改什么才能正常工作?
提前致谢!
最佳答案
这是我的实现:
vec_struct.cpp
#include "mex.h"
#include <vector>
// C++ struct
struct Point3D {
double x, y, z;
};
struct myStruct {
Point3D start;
Point3D end;
double length;
};
const char *fieldsPoint[] = {"x", "y", "z"};
const char *fieldsStruct[] = {"start", "end", "length"};
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
if (nrhs != 0 || nlhs > 1) {
mexErrMsgIdAndTxt("MATLAB:MEX", "Wrong number of arguments.");
}
// create C++ vector of structs
std::vector<myStruct> v;
for (int i=0; i<10; i++) {
myStruct s = {
{1.0+i, 2.0+i, 3.0+i},
{4.0+i, 5.0+i, 6.0+i},
i
};
v.push_back(s);
}
// convert it to MATLAB struct array and return it as output
mxArray *p;
plhs[0] = mxCreateStructMatrix(1, v.size(), 3, fieldsStruct);
for (int i=0; i<v.size(); i++) {
// start point
p = mxCreateStructMatrix(1, 1, 3, fieldsPoint);
mxSetField(p, 0, "x", mxCreateDoubleScalar(v[i].start.x));
mxSetField(p, 0, "y", mxCreateDoubleScalar(v[i].start.y));
mxSetField(p, 0, "z", mxCreateDoubleScalar(v[i].start.z));
mxSetField(plhs[0], i, "start", p);
// end point
p = mxCreateStructMatrix(1, 1, 3, fieldsPoint);
mxSetField(p, 0, "x", mxCreateDoubleScalar(v[i].end.x));
mxSetField(p, 0, "y", mxCreateDoubleScalar(v[i].end.y));
mxSetField(p, 0, "z", mxCreateDoubleScalar(v[i].end.z));
mxSetField(plhs[0], i, "end", p);
// length
mxSetField(plhs[0], i, "length", mxCreateDoubleScalar(v[i].length));
}
}
我们从MATLAB编译并调用MEX函数:
>> mex -largeArrayDims vec_struct.cpp
>> s = vec_struct()
s =
1x10 struct array with fields:
start
end
length
如您所见,这将创建一个长度为10的structure array。例如,第5个结构的访问方式为:
>> s(5)
ans =
start: [1x1 struct]
end: [1x1 struct]
length: 4
>> s(5).start
ans =
x: 5
y: 6
z: 7
>> s(5).start.x
ans =
5
上面的MEX文件等效于以下MATLAB代码:
ss = struct();
for i=1:10
ss(i).start = struct('x',1+i-1, 'y',2+i-1, 'z',3+i-1);
ss(i).end = struct('x',4+i-1, 'y',5+i-1, 'z',6+i-1);
ss(i).length = i-1;
end