VIPS includes a set of functions for memory allocation local to an image
descriptor. The base memory allocation function is im_malloc()
. It
has type:
char *im_malloc( IMAGE *im, int size )
It operates exactly as the standard malloc()
C library function,
except that the area of memory it allocates is local to image descriptor
im
. If im_malloc()
is unable to allocate memory, it returns
NULL
. If you pass NULL
instead of a valid image descriptor,
then im_malloc()
allocates memory globally and you must free it
yourself at some stage.
To free memory explicitly, use im_free()
:
int im_free( void *mem )
im_free()
always returns 0, so you can use it as an argument to a
callback.
Three macros make memory allocation even easier. IM_NEW()
allocates
a new object. You give it a descriptor and a type, and it returns a pointer
to enough space to hold an object of that type. It has type:
type-name *IM_NEW( IMAGE *im, type-name )
The second macro, IM_ARRAY()
, is very similar, but allocates
space for an array of objects. Note that, unlike the usual calloc()
C library function, it does not initialise the array to zero. It has type:
type-name *IM_ARRAY( IMAGE *im, int n, type-name )
Finally, IM_NUMBER()
returns the number of elements in an array of
defined size. See the man pages for a series of examples, or
see §4.1.