Dynamic Matrix

[Engeletrica]

Hello Everyone!!

I need construct a matrix where the values are dynamic.
For example:

[asmboy]

perhaps you would like to show a more complete program -
that actually COMPILES??

[Brandon03]

There are two common approaches. For N rows with M columns each:

One is to simulate the matrix with a one-dimensional array. You
allocate space for N*M objects, as with
T *ptr = malloc(N * M * sizeof *ptr);
and you reference the (i,j)th element by calculating the appropriate
subscript yourself, as in
ptr[i*M+j] = 0;

The other is to build an array of pointers, each pointing to one
row of the matrix, as in
T **ptr = malloc(N * sizeof *ptr);
for (k = 0; k < N; k++)
ptr[k] = malloc(M * sizeof *ptr[k]);
and you reference the (i,j)th element using the natural syntax, as in
ptr[i][j] = 0;

In either case, you pass the array to a function by using the ptr
variable. Note, since N and M are not known until run time:

Using the first approach always requires M to be available to the
function.

In either approach, the function will need both N and M if it is
concerned in any way with the top or right boundary elements of the
matrix.

The second approach is more flexible in that it can handle jagged
arrays where M is not constant for each row.


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