IM_LIST_ADD(3)

NAME
im_list_add, im_list_len, im_list_pos, im_list_member, im_list_append, im_list_remove, im_list_eq, im_list_map, im_list_map_rev, im_list_fold, im_list_fix, im_list_free, im_list_insert - linked list functions

SYNOPSIS
#include <vips/vips.h>
#include <vips/list.h> typedef struct list_type {
    struct list_type *next;
    void *this;
} List; #define hd(L) ((L)->this)
#define tl(L) ((L)->next) typedef void *(*im_list_map_fn)( void *, void *, void * );
typedef void (*im_list_free_fn)( void *, void *, void * );
typedef void *(*im_list_fold_fn)( void *, void *,
    void *, void * ); int im_list_len( List *l );
int im_list_pos( List *l, void *t );
int im_list_member( List *l, void *t );
void *im_list_index( List *l, int n );
int im_list_add( List **base, void *new );
int im_list_insert( List **base, void *new, void *old );
int im_list_append( List **base, void *new );
int im_list_remove( List **base, void *t ); void *im_list_eq( void *a, void *b );
void *im_list_map( List *l,
    im_list_map_fn fn, void *a, void *b );
void *im_list_map_rev( List *l,
    im_list_map_fn fn, void *a, void *b );
void *im_list_fold( List *l,
    void *start, im_list_fold_fn fn, void *a, void *b );
void im_list_fix( List **base,
    im_list_map_fn fn, void *a, void *b );
void im_list_free( List **base,
    im_list_free_fn fn, void *a, void *b );

DESCRIPTION
Manipulate linked lists in various ways. These functions are heavily used by the VIPS IO system; use them yourself if you like. VIPS lists store lists of void * pointers - use casts if you want to store some other type. Note that if sizeof( your object ) != sizeof( void * ), you will be in trouble! All are based on the List type (see above). An empty list is a NULL pointer, a one element list is a pointer to a List struct, whose this field contains a pointer to the object in the list and whose next field is NULL. Macros hd(3) and tl(3) (head and tail) return this and next respectively. im_list_len(3) returns the number of elements in list l. im_list_pos(3) searches list l for stored object t, returning an index. The first list element has index zero. im_list_pos(3) returns -1 for not present. im_list_index(3) returns the item at position n in the list, or NULL for index out of range. im_list_member(3) returns non-zero if the list contains the element. im_list_map(3) applies a void * valued function to every element in a list, running from beginning to end. If the function returns NULL, im_list_map continues with the next element. If the function returns non-NULL, im_list_map(3) abandons the map and returns immediately, returning the value the user function returned. If the list is empty, im_list_map(3) returns NULL. The two extra arguments a and b are carried around for you by VIPS and fed into each call of the function. They are useful for communicating context information. You can use im_list_map to implement many kinds of list search/apply operation. VIPS supplies the function im_list_eq(3) which tests two void * pointers for equality, returning the pointer if they match, and returning NULL otherwise. Example: search a list for an object
    im_list_map( list,
         (im_list_map_fn) im_list_eq, object, NULL ); This could also be written as
    List *p;
    for( p = list; p; p = tl( p ) )
        if( object == hd( p ) )
            break; I prefer the first. im_list_map_rev(3) behaves exactly as im_list_map(3), but applies the function running from te end to the beginning of the list. It is much slower than im_list_map(3) and should be used only in emergencies. im_list_fold(3) folds up a list with a dyadic function. If a list contains [1,2], return fn( 2, fn( 1, start, a, b ), a, b ). If the list is empty, return start. The two extra arguments a and b are carried around for you by VIPS and fed into each call of the function. They are useful for communicating context information. Example: find a pointer to the largest element in a list of ints (assume sizeof(int) <= sizeof(void *))
    max_pair( int *new, int *old )
    {
        if( !old || *new > *old )
            return( new );
        else
            return( old );
    }
    largest = im_list_fold( list,
        NULL, (im_list_map_fn) max_pair, NULL, NULL ); im_list_add(3) adds a new element to the head of a list. Since the head of the list will move, you must pass in a *pointer* to your pointer to your old head. Example: make a list of the numbers 9-0 (assume sizeof(int) <= sizeof(void *))
    int i;
    List *nlist = NULL;
    for( i = 0; i < 10; i++ )
        im_list_add( &nlist, (void *) i ); im_list_insert(3) adds a new element to a list, placing it just before the indicated old element. If the old element is not found, im_list_insert(3) returns an error. im_list_append(3) appends a new element to the end of a list. This is much slower than im_list_add(3), and should be avoided if possible. im_list_remove(3) removes the specified element from the list. Since the head of the list may move, you must pass in a *pointer* to your pointer to your old head. im_list_fix(3) finds the fixed-point of a list-altering function. It repeatedly maps a function over the list until the function returns NULL. Note that, since the list may be changing, you must pass in a *pointer* to the pointer you store the list in. The two extra arguments a and b are carried around for you by VIPS and fed into each call of the function. They are useful for communicating context information. Example: remove all elements less than x from a list of numbers (assume sizeof(int) <= sizeof(void *))
    int *
    test_ele( int *n, List **base, int x )
    {
        if( *n < x ) {
            im_list_remove( base, n );
            return( base );
        }
        else
            return( NULL );
    }
    im_list_fix( &nlist,
        (im_list_map_fn) test_ele, &nlist, x ); im_list_free(3) frees the list, applying a user free function to every element as it is freed. You may pass NULL instead of a pointer to a function, in which case im_list_free(3) will just free the memory used by the list nodes. The two extra arguments a and b are carried around for you by VIPS and fed into each call of the function. They are useful for communicating context information.

RETURN VALUE
The functions returns a 0 or a pointer on sucess, and non-zero or NULL on failure.

SEE ALSO
im_rect_intersectrect(3), etc.

COPYRIGHT
National Gallery, 1992

AUTHOR
J. Cupitt