How to name a variable with index to store the input mxArray?

Question

I want to realize a function to translate the input variable of mxArray(from Matlab) to C++. For detail, if the input variable is a cell, it will be arranged to a vector.(Edited following advices) Like below,

#include "mex.h"
#include <vector>
#include <iostream>
#include <algorithm>
#include <omp.h>
#include <map>
#include <string>
using namespace std;

vector<vector<int>> transfer(const mxArray* ix)
{
    mwSize Num = mxGetNumberOfElements(ix);
    mxArray* ptr = NULL;
    mxDouble* ptr_double;
    vector<vector<int>> V(Num);
    mwSize Num0;
    int i,j;
    for (i = 0; i < (int)Num; i++) {
        ptr = mxGetCell(ix, i);
        Num0 = mxGetNumberOfElements(ptr);
        ptr_double = mxGetPr(ptr);
        for (j = 0; j < (int)Num0; j++) {
            V[i].push_back(*ptr_double++);
        }
    }
    return V;
}
void mexFunction(int nlhs, mxArray* plhs[], int nrhs, const mxArray* prhs[])
{
    for (int i = 0; i < nrhs; i++) {
        if (mxIsCell(prhs[i])) {
            vector<vector<int>>  V1 = transfer(prhs[i]);
            for (int j = 0; j < V1.size(); j++)
            {   
                for (int k = 0; k < V1[j].size(); k++) {
                    mexPrintf("  %d", V1[j][k]);
                }
                mexPrintf("\n size is %d\n", V1[j].size());
            }
        }
       //else
    }
    return;
}

I now have a problem to name the above variable. I have to name the variable (like V1) corresponding to the index i(1 in the example). But I don't know how to realize it in c++. Could you tell me how to do it in C++?

I have searched a little on Internet and I found it seems impossible to have an dynamic name in C++. If this is true, Could anyone have some idea how to arrange these input variables, which type is vector> and double array? Perhaps struct? Then how to initial the struct dynamically is a bigger challenge to me. Besides, I want to do this because I am using OpenMP which could not have any variable or pointer related to Matlab in the parallel loops. I must copy all the data from mx- to C++ supported type data(like vector).

Answer 1

Maybe something like this:

#include "mex.h"
#include <vector>
#include <iostream>
#include <algorithm>
#include <omp.h>
#include <map>
#include <string>
using namespace std;

vector<vector<double>> transfer(const mxArray* ix) // changed to double
{
    mwSize Num = mxGetNumberOfElements(ix);
    mxArray* ptr = NULL;
    mxDouble* ptr_double;
    vector<vector<double>> V(Num); // changed to double
    mwSize Num0;
    int i,j;
    for (i = 0; i < (int)Num; i++) {
        ptr = mxGetCell(ix, i);
        if( ptr ) { // check for NULL pointer
            if( !mxIsDouble(ptr) || mxIsComplex(ptr) || mxIsSparse(ptr) ) { // check for proper type etc.
                mexErrMsgTxt("cell must contain full real double");
            }
            Num0 = mxGetNumberOfElements(ptr);
            ptr_double = mxGetPr(ptr);
            for (j = 0; j < (int)Num0; j++) {
                V[i].push_back(*ptr_double++);
            }
        }
    }
    return V;
}
void mexFunction(int nlhs, mxArray* plhs[], int nrhs, const mxArray* prhs[])
{
        for (int i = 0; i < nrhs; i++) {
        if (mxIsCell(prhs[i])) {
            vector<vector<double>>  V1 = transfer(prhs[i]); // changed to double
            for (int j = 0; j < V1.size(); j++)
            {   
                for (int k = 0; k < V1[j].size(); k++) {
                    mexPrintf("  %g", V1[j][k]); // changed to %g
                }
                mexPrintf("\n size is %d\n", V1[j].size());
            }
        }
       //else
    }
    return;
}

Answer 2

Divide function.

BTW, new mxArray * [Num] is bad idea. use std::vector<mxArray>

void transfer_impl(vector<vector<int>>& V, mxDouble*& ptr, mwSize Num0){
    for (mwSize i = 0; j < Num0; j++) {
        V[i].push_back(*ptr_double++);
    }
}

Because the OpenMP is always crash

You should consider using C++17 Parallel Algorithms.