Answers to Frequently Asked Questions (FAQ) on comp.lang.c

[Steve Summit]

In article <1990Aug1.042116.20244 at athena.mit.edu> I wrote:
>A:  It is usually best to allocate an array of pointers, and then
>    initialize each pointer to a dynamically-allocated "row."
>
>         int **array = (int **)malloc(nrows * ncolumns * sizeof(int *));
>         for(i = 0; i < nrows; i++)
>                 array[i] = (int *)malloc(ncolumns * sizeof(int));

This code wastes space and is misleading.  The initial "dope
vector" need only contain a pointer for each row of the intended
array, not each element:

          int **array = (int **)malloc(nrows * sizeof(int *));

The same problem afflicts the second posted 2D allocation
example, as well.

Thanks to Freek Wiedijk for pointing this out.

                                            Steve Summit
                                            scs at adam.mit.edu