.TH IM_LIST_ADD 3 "2 May 1991" .SH 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 .SH SYNOPSIS #include .br #include typedef struct list_type { .br struct list_type *next; .br void *this; .br } List; #define hd(L) ((L)->this) .br #define tl(L) ((L)->next) typedef void *(*im_list_map_fn)( void *, void *, void * ); .br typedef void (*im_list_free_fn)( void *, void *, void * ); .br typedef void *(*im_list_fold_fn)( void *, void *, .br void *, void * ); int im_list_len( List *l ); .br int im_list_pos( List *l, void *t ); .br int im_list_member( List *l, void *t ); .br void *im_list_index( List *l, int n ); .br int im_list_add( List **base, void *new ); .br int im_list_insert( List **base, void *new, void *old ); .br int im_list_append( List **base, void *new ); .br int im_list_remove( List **base, void *t ); void *im_list_eq( void *a, void *b ); .br void *im_list_map( List *l, .br im_list_map_fn fn, void *a, void *b ); .br void *im_list_map_rev( List *l, .br im_list_map_fn fn, void *a, void *b ); .br void *im_list_fold( List *l, .br void *start, im_list_fold_fn fn, void *a, void *b ); .br void im_list_fix( List **base, .br im_list_map_fn fn, void *a, void *b ); .br void im_list_free( List **base, .br im_list_free_fn fn, void *a, void *b ); .SH 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, .br (im_list_map_fn) im_list_eq, object, NULL ); This could also be written as List *p; for( p = list; p; p = tl( p ) ) .br if( object == hd( p ) ) .br 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 ) .br { .br if( !old || *new > *old ) .br return( new ); .br else .br return( old ); .br } largest = im_list_fold( list, .br 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; .br List *nlist = NULL; for( i = 0; i < 10; i++ ) .br 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 * .br test_ele( int *n, List **base, int x ) .br { .br if( *n < x ) { .br im_list_remove( base, n ); .br return( base ); .br } .br else .br return( NULL ); .br } im_list_fix( &nlist, .br (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. .SH RETURN VALUE The functions returns a 0 or a pointer on sucess, and non-zero or NULL on failure. .SH SEE\ ALSO im_rect_intersectrect(3), etc. .SH COPYRIGHT .br National Gallery, 1992 .SH AUTHOR J. Cupitt