pass a pointer-to-pointer, or return a pointer? Post: 302273896

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Top Forums Programming pass a pointer-to-pointer, or return a pointer? Post 302273896 by spirtle on Tuesday 6th of January 2009 05:43:33 AM

01-06-2009

Registered User

I prefer the second form because:

The interface is simpler: one parameter in, the answer returned. You just check whether the pointer is null to verify success. The first form has some kind of other return value to check, which could be boolean, but I cannot tell, so I would have to look up the definitions of OK and NOK. And it is unclear from the interface whether I also need to check the pointer value, or indeed whether the pointer is NULL on failure. Looking into you implementation I can see that OK is returned if and only if the pointer is valid and the pointer is NULL on failure, but then I can write
Code:
```
char *my_pmem;
my_malloc(64, &my_pmem);
if(my_pmem){
  ...
}
```
so the return value is redundant -- it gives me no extra information.
However, if you want the function to indicate more than just a simple fail/succeed (e.g. different failure modes) then the first way is the only way to do it.
It mimics the standard malloc(3) function -- or it would do if the parameter was of type size_t rather than int -- and therefore has the benefit of familiarity, and makes it easier to port code written with malloc to use my_malloc.

spirtle

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allocb

allocb(9r)																allocb(9r)

NAME

       allocb - STREAMS: Allocates a message block

SYNOPSIS

       #include <sys/stream.h>

       MBLKP allocb(
	       int size,
	       uint pri );

ARGUMENTS

       Specifies the number of bytes in the message block.  Specifies the priority of the request. You use this argument to determine if the allo-
       cation of memory blocks (waits) on the request. If you call the allocb interface at a high priority and it blocks on the request, the  sys-
       tem could deadlock. Typically, you pass the constant BPRI_WAITOK, which signifies that allocb can block. If allocb cannot block, you should
       pass the BPRI_HI constant.

DESCRIPTION

       The allocb interface attempts to allocate a STREAMS message block. Buffer allocation fails only when the system is out of  memory.   If	no
       buffer is available, you can call the bufcall interface, which helps a module recover from a memory allocation failure.

RETURN VALUES

       Upon  successful  completion,  the  allocb interface returns a pointer to the allocated message block. This message block is of type struct
       msgb *. The msgb data structure is defined in the /usr/sys/include/sys/stream.h file.

       If allocb cannot allocate a message block, it returns a NULL pointer.

SEE ALSO

       Kernel Routines: bufcall(9r), esballoc(9r), testb(9r)

       Programmer's Guide: STREAMS

																	allocb(9r)