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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debugfs_create_bool

DEBUGFS_CREATE_BOOL(9)					      The debugfs filesystem					    DEBUGFS_CREATE_BOOL(9)

NAME

       debugfs_create_bool - create a debugfs file that is used to read and write a boolean value

SYNOPSIS

       struct dentry * debugfs_create_bool(const char * name, mode_t mode, struct dentry * parent, u32 * value);

ARGUMENTS

       name
	   a pointer to a string containing the name of the file to create.

       mode
	   the permission that the file should have

       parent
	   a pointer to the parent dentry for this file. This should be a directory dentry if set. If this parameter is NULL, then the file will
	   be created in the root of the debugfs filesystem.

       value
	   a pointer to the variable that the file should read to and write from.

DESCRIPTION

       This function creates a file in debugfs with the given name that contains the value of the variable value. If the mode variable is so set,
       it can be read from, and written to.

       This function will return a pointer to a dentry if it succeeds. This pointer must be passed to the debugfs_remove function when the file is
       to be removed (no automatic cleanup happens if your module is unloaded, you are responsible here.) If an error occurs, NULL will be
       returned.

       If debugfs is not enabled in the kernel, the value -ENODEV will be returned. It is not wise to check for this value, but rather, check for
       NULL or !NULL instead as to eliminate the need for #ifdef in the calling code.

COPYRIGHT

Kernel Hackers Manual 2.6.					     July 2010						    DEBUGFS_CREATE_BOOL(9)