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

Sponsored Content

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

View Public Profile for spirtle

Find all posts by spirtle

10 More Discussions You Might Find Interesting

1. Programming

pointer

void main() { int a={1,2,3,4,5,6,7,8,9,10}; int *p=a; int *q=&a; cout<<q-p+1<<endl; } The output is 10, how? if we give cout<<q it will print the address, value won't print.... if we give cout<<p it will print the address, value won't print.... p has the base addr; q...

2. Programming

Regarding char Pointer

Hi, char *s="yamaha"; cout<<s<<endl; int *p; int i=10; p=&i; cout<<p<<endl; 1) For the 1st "cout" we will get "yamaha" as output. That is we are getting "content of the address" for cout<<s. 2) But for integer "cout<<p" we are getting the "address only". Please clarify how we are...

3. Programming

pointer problem

could any one tell why the following is showing segmentation fault while using **ptr but working fine using **a #include<stdio.h> ...

4. Programming

far pointer

what is far pointer in C

5. Programming

How to return void function pointer

Hello all im trying to build function that will return void function pointer what is mean is ( not working ) the main function void * myClass::getFunction(int type){ if(type==1) return &myClass::Test1; if(type==2) return &myClass::Test2; } void myClass::Test1(){...

6. Programming

matrix pointer

Can anyone tell me what the following statements do? float (*tab); tab=(float (*)) calloc(MAXCLASS, (MAXCLASS+1)*sizeof(float));

7. Programming

Pointer Arithmetic In C

I have a fundamental question on C pointer arithmetry.. Suppose i have a c string pointer already pointing to a valid location, Can I just do a charptr = charptr +1; to get to the next location, irregardless if my program is 32 or 64 bits? or should i do it this way: charptr =...

8. Programming

Pointer to pointers

Hi guys, I'm trying to understand pointers in C and made a simple example and I've problems with It. Can someone help? #include <stdio.h> #include <stdlib.h> #include <assert.h> int f1(char **str_); int main(int argc, char **argv) { char *str = NULL; f1(&str); ...

9. Programming

Pointer for 2D array seems to be 3D in C

I am struggling with the pointer to 2D-array (cf: 2D array of pointers). Can anybody help me elaborate how the pointer x moves in the memory to access the individual of y, especially the high lighted lines? I have talked to one of the curators of the forum, but I am still not quite clear. Here...

10. Programming

Segmentation fault when I pass a char pointer to a function in C.

I am passing a char* to the function "reverse" and when I execute it with gdb I get: Program received signal SIGSEGV, Segmentation fault. 0x000000000040083b in reverse (s=0x400b2b "hello") at pointersExample.c:72 72 *q = *p; Attached is the source code. I do not understand why...

LEARN ABOUT HPUX

xtrealloc

XtRealloc()															       XtRealloc()

Name
  XtRealloc - change the size of an allocated block of storage.

Synopsis
  char *XtRealloc(ptr, num);
	 char *ptr;
	 Cardinal num;

Inputs
  ptr	    Specifies a pointer to memory allocated with XtMalloc(), XtCalloc(), or XtRealloc(), or NULL.

  num	    Specifies the new number of bytes of memory desired in the block.

Returns
  A pointer to allocated memory.

Description
  XtRealloc() changes the size of the block of allocated memory pointed to by ptr to be at least num bytes large.  In order to make this size
  change, it may have to allocate a new block of memory and copy the contents of the old block (or as much as will fit) into the  new  block.
  If  it  allocates a new block of memory, it frees the old block.  In either case, it returns a pointer to a block of memory which is of the
  requested size.  If there is insufficient memory to allocate the new block, XtRealloc() terminates by calling XtErrorMsg().

  If ptr is NULL, XtRealloc() simply calls XtMalloc() to allocate a block of memory of the requested size.

Usage
  Note that XtRealloc() may move the contents of your allocated memory to a new location; the return value may or may not be the same as ptr.
  Not  all  memory can be safely reallocated.  If there are multiple pointers to a block of memory scattered through out an application (such
  as pointers to a widget record), then reallocating that memory is not safe, because all pointers to it cannot  be  updated.	Other  memory
  (such  as  the array of children maintained privately by the Composite widget class) can be safely updated because there should be only one
  pointer to it in the application (in this case the pointer is the composite.children field of the widget).  These cautions are no different
  than those required with the standard realloc() function.

  In most cases, you will have to cast the return value of XtRealloc() to an appropriate pointer type.

  Note that because XtRealloc() behaves like XtMalloc() when passed a NULL pointer, (something that realloc() does not do), you don't have to
  write special case code to allocate the first chunk of memory with XtMalloc() and subsequent chunks with XtRealloc(); you  can  simply  use
  XtRealloc() everywhere.

  Memory  allocated with XtRealloc() must be deallocated with XtFree().  The function XtRealloc() is implemented by the Toolkit independently
  of the particular environment, so programs ported to a system not supporting malloc will still work.

See Also
  XtCalloc(1), XtFree(1), XtMalloc(1), XtNew(1), XtNewString(1).

Xt - Memory Allocation														       XtRealloc()