help needed about dynamic space allocation

[Alastair Adamson]

In article <1046 at lifia.UUCP> fano at lifia.UUCP (Rampa*) writes:
>
>  float **sig;                                    /* matrix declaration     */
>  ....
>  sig = (int *)malloc(n * sizeof(int));           /* allocates space for sig */
>
>during the compiling time, I get the following warning:
>     "combin1.c", line 220: warning: illegal pointer combination

Try changing the initialisation of sig to
	sig = (float **)malloc(n * sizeof(float *));
and the warning message will go away. Since sig is a double pointer to
a float, that is what you want malloc to return. You are creating a dope
vector, where each element of the vector is in fact a pointer a row
which in turn is a pointer to the elements of that row; thus:

	---		-----------
	| |------------>|         |
	| |-----        -----------
	---     |
	        |       -----------
	        ------->|         |
			-----------
The technique is common. Each element of the 2-dimensional table is float.
Thus the pointer to each row is a (float *). Sig points to these row pointers
ans is thus is (float **).

By the way, another solution which uses less memory is simplt to
get hold of enough space for all the elements of the table and do
the addressing yourself. For example a N x M table can be dealt with:

	table = (type *)malloc(N * M * sizeof(type));
	...
	table[i * N + j] = value;	/* put value in table[i][j] */
	...
	free((char *)table);		/* free the space */

Alternatively, to make acceses *look* better, use
#define	Table(i, j)	table[i * N + j]
and
	Table(i, j) = value;

Bonne chance,
	Alastair