use of if (!cptr) and if (cptr), where cptr is a *

[John Hascall]

In article <10099 at mpx2.mpx.com> erik at mpx2.mpx.com (Erik Murrey) writes:
>I'm curious how the gods feel about testing pointers in the following
>way (by example):

   Well, I'm probably not even a minor diety (yet :-) but here's an
   example of what I use:

-------------------------- macro.h ------------------------------------------


#define ALLOC(type,count)         \    
    ((type*)malloc(count*sizeof(type)))

#define FATAL(string,val)         \                                          
    return(fprintf(stderr, "[%4d] 0x0%x <- %s",  __LINE__, val, string), val)

#define ALLOCATE(ptr,type,count)  \                                            
    if ((ptr=ALLOC(type,count)) == NULL) FATAL("alloc(ptr, type, count)", NULL)

#define SYSCALL(function)         \                  
    if (((syscall_status = function)&1) == 0) FATAL("function", syscall_status)

static int syscall_status;

---------------------------- foo.c -----------------------------------------

#include <descrip.h>
#include <stdio.h>  
#include <stdlib.h> 
#include "macro.h"

typedef struct foo {
        int     bar;
        int     baz;
} FOO;              

main(argc,argv) 
int     argc;   
char    *argv[];
{               
        $DESCRIPTOR(    device, "ZZA0:");
        unsigned short  channel;         
        FOO             *cptr;           
        int             n_foo;           

        n_foo = atoi(argv[1]);                       
        ALLOCATE(cptr, FOO, n_foo);                  
        SYSCALL(sys$assign(&device, &channel, 0, 0));
}

-------------------------------------------------------------------

The SYSCALL macro really has nothing to do with memory allocation,
it just happens to be in my "macro.h" file with the others, (it is
a VMS-ism to boot), so I thought I'd through it out anyway.

I wish I could come up with better names than "ALLOC" and "ALLOCATE"
-- they are *too* similar.

John Hascall  /  ISU Comp Center  /  Ames IA