Depends on your exact needs, if all you care about is accessing elements as
mat[i][j] you can do something like this:
int** matrix;
...
matrix = new int*[M]; // create an array of pointers to int
for (int i = 0; i < M; ++i)
matrix[i] = new int[N]; // create an array of integers for each "row"
// now matrix[i][j] should work as expected
// you can free memory like this
for (int i = 0; i < M; ++i)
delete[] matrix[i]; // delete each array of integers
delete[] matrix; // delete the array of pointers
Creating that way, is simple and intuitive, but has the disadvantage that
the elements are not contiguous in the matrix, each row has it's elements
contiguous, but not the complete matrix. That means, that a function that
expects a "normal" matrix and uses the fact that something like "int
mat[3][4]" has the 12 values contiguous may break.
A work around for that is to create the contiguous array of size MxN and
then assign the correct pointers, something like:
int** matrix;
...
int* temp = new int[M * N]; // contiguous array for the integers
matrix = new int*[M]; // create an array of pointers to int
for (int i = 0; i < M; ++i)
matrix[i] = temp + N * i; // Make each element of "matrix" point to the
start of the corresponding row
// NOTE: DO NOT DELETE temp, for extra safety, make it a null pointer
temp = 0;
// now matrix[i][j] should work as expected, also, all elements are
contiguous
// you can free memory like this
delete[] matrix[0]; // delete the contiguous array of integers
delete[] matrix; // delete the array of pointers
You can extend this idea for any number of dimensions you like.
Regards,
Carlos Guía
On Tue, May 15, 2012 at 8:18 AM, Registered user
<[email protected]>wrote:
> how to create 2d or 3d array dynamically , giving the size at run time :
> for global array....
>
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