vander@nssdcb.gsfc.nasa.gov (John Vanderpool) (08/01/90)
does the free() function return anything?
in VAXC v3.0 it's defined as: void free (void *ptr);
i though it used to (just to tell you it was successful)
- was that an incorrect implementation ?
if the argument is void *ptr how does it know how many bytes to release?
which brings me to my example (attached) do i need to cast the pointer
before free()ing it?
thanx, hope this isn't too stupid!
fish
------------------------------------------------------------------------------
/* each type of XAB is a different size structure on VAX/VMS for unix folks */
#include xab
#define NULL (void *) 0
void RMS_free_XABchain( struct XABKEY *xabp )
/* originally had as void *xabp but then you can't reference its
elements */
{
/* cast XAB pointer using XAB type code in xab$b_cod */
switch( xabp->xab$b_cod )
{
case XAB$C_ALL : xabp = (struct XABALL *) xabp; break;
case XAB$C_DAT : xabp = (struct XABDAT *) xabp; break;
case XAB$C_FHC : xabp = (struct XABFHC *) xabp; break;
case XAB$C_KEY : xabp = (struct XABKEY *) xabp; break;
case XAB$C_PRO : xabp = (struct XABPRO *) xabp; break;
case XAB$C_RDT : xabp = (struct XABRDT *) xabp; break;
case XAB$C_SUM : xabp = (struct XABSUM *) xabp; break;
case XAB$C_TRM : xabp = (struct XABTRM *) xabp; break;
default : printf( "bad xab code=%d\n", xabp->xab$b_cod ); return;
} /* end switch */
/* recursively call until end of chain is reached, free on unwind */
if( xabp != NULL )
{
RMS_free_XABchain( xabp->xab$l_nxt );
free( xabp );
}
} /* RMS_free_XAB_chain */karl@haddock.ima.isc.com (Karl Heuer) (08/01/90)
In article <2958@dftsrv.gsfc.nasa.gov> vander@nssdcb.gsfc.nasa.gov writes: >does the free() function return anything? No. >in VAXC v3.0 it's defined as: void free (void *ptr); >i though it used to (just to tell you it was successful) > - was that an incorrect implementation ? Since free() cannot fail unless the program is already seriously broken, there's not much point. It might as well use abort() to flag the error. >if the argument is void *ptr how does it know how many bytes to release? Magic. (I mean that seriously.) It's not something the user needs to be concerned with; the implementation will remember the size somehow. >which brings me to my example (attached) do i need to cast the pointer >before free()ing it? You should be okay as long as `free()' has been declared with a prototype. (It's sufficient to #include <stdlib.h> if your compiler is ANSI-compliant.) On a compiler without prototypes, you should cast the argument to `char *' (or `void *' if you have it, but this is also an ANSI invention) for complete portability. (It looks like *this* code will never be ported off a vax anyway, but it's good programming practice, and makes lint happy.) >void RMS_free_XABchain( struct XABKEY *xabp ) >/* originally had as void *xabp but then you can't reference its elements */ If this is a pointer to a generic class of structs that all share a common initial member, you could use `void *xabp' and reference the common member with `((struct XABKEY *)xabp)->xab$b_cod'. > case XAB$C_ALL : xabp = (struct XABALL *) xabp; break; This almost certainly isn't what you want. Karl W. Z. Heuer (karl@kelp.ima.isc.com or ima!kelp!karl), The Walking Lint