On Mon, 15 Jan 2001, Rhonda Frances Bailey wrote:
> hi all!
>
> we have a program:
>
>
> /* Prototypes */
> void GJFullPivotInvert(int rank, const double **ar, double **target);
> void PrintMatrixD(int rank, double **ar);
>
> #include<stdio.h>
> int main(void)
> {
> double A[3][3] = {{1.0,2.0,3.0},{4.0,5.0,6.0},{7.0,8.0,9.0}};
> double inverse[3][3];
>
> GJFullPivotInvertD(rank, A, inverse);
> PrintMatrixD(3, inverse);
>
> return(0);
> }
>
>
> inverse will be initialized in GJFullPivotInvertD.
>
> gcc complains about the call to PrintMatrix, but not about the call to
> GJFullPivotInvertD(). here is the error:
>
> example.c: In function `main':
> example.c:32: warning: passing arg 2 of `PrintMatrixD' from incompatible pointer type
>
> can anyone shed light on this seeming inconsistency?
Very strange. Both calls are invalid. I don't know why one succeeds.
The memory allocated for variable "inverse" is 9 consecutive doubles.
The type of "inverse" is an array of arrays, which C can interpret as
a pointer to an array. Upon dereferencing that pointer, you do not
find another pointer located in that memory! Thus, using "**" is invalid
in both calls.
To use this approach, you would have to try something like:
double **inverse;
int i;
if ( NULL == ( inverse = (double **) calloc( 3, sizeof(double *) ))) exit( 1 );
for ( i = 0 ; i < 3 ; i++ ) {
if ( NULL == ( inverse[ i ] = calloc( 3, sizeof( double ) ) ) ) break;
}
if ( NULL == inverse[ 2 ] ) { /* not all columns allocated */
for ( i = 1 ; i >= 0 ; --i )
if ( NULL != inverse[ i ] ) free( inverse[ i ];
free( inverse );
exit( 1 );
}
/* inverse successfully allocated */
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