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Path: utzoo!mnetor!seismo!mcvax!inria!axis!alastair
From: alastair@axis.UUCP (Alastair Adamson)
Newsgroups: comp.lang.c
Subject: Re: help needed about dynamic space allocation
Message-ID: <769@axis.UUCP>
Date: Sun, 23-Nov-86 06:36:14 EST
Article-I.D.: axis.769
Posted: Sun Nov 23 06:36:14 1986
Date-Received: Mon, 24-Nov-86 21:48:07 EST
References: <13802@amdcad.UUCP> <359@prairie.UUCP> <1046@lifia.UUCP>
Reply-To: alastair@axis.UUCP (Alastair Adamson)
Organization: Axis Digital, 135 rue d'Aguesseau, Boulogne, 92100, FRANCE
Lines: 44
Keywords: malloc()

In article <1046@lifia.UUCP> fano@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