Is it possible in c++ for a class to have a member which is a multidimensional array whose dimensions and extents are not known until runtime?

Question

I originally asked using nested std::array to create an multidimensional array without knowing dimensions or extents until runtime but this had The XY Problem of trying to a

Answer 1

Instead of a multidimensional array you could use a 1D-array with an equal amount of indices. I could not test this code, but I hope it will work or give you an idea of how to solve your problem. You should remember that arrays, which do not have a constant length from the time of being compiled, should be allocated via malloc() or your code might not run on other computers. (Maybe you should create a class array for the code below)

#include 

int* IndexOffset; //Array which contains how many indices need to be skipped per  dimension
int  DimAmount;   //Amount of dimensions
int  SizeOfArray = 1; //Amount of indices of the array

void AllocateArray(int* output,         //pointer to the array which will be allocated
                   int* dimLengths,     //Amount of indices for each dimension: {1D, 2D, 3D,..., nD}
                   int dimCount){       //Length of the array above

DimAmount = dimCount;
int* IndexOffset = (int*) malloc(sizeof(int) * dimCount);
int temp = 1;

for(int i = 0; i < dimCount; i++){

temp = temp * dimLengths[i];
IndexOffset[i] = temp; 

}


for(int i = 0; i < dimCount; i++){

SizeOfArray = SizeOfArray * dimLengths[i];

}

output = (int*)malloc(sizeof(int) * SizeOfArray);

}

To get an index use this:

int getArrayIndex(int* coordinates //Coordinates of the wished index as an array (like dimLengths)
            ){

int index;
int temp = coordinates[0];

for(int i = 1; i < DimAmount; i++){

     temp = temp + IndexOffset[i-1] * coordinates[i];

}
index = temp;
return index;
}

Remember to free() your array as soon as you do not need it anymore:

for(int i = 0; i < SizeOfArray; i++){

    free(output[i]);

}
free(output);