tsearch, tfind, tdelete, twalk - manage a binary tree


#include key, void **rootp, int (compar)(const void , const void )); void *tfind (const void *key, const void **rootp, int (compar)(const void *, const void *)); void *tdelete (const void *key, void **rootp, int (compar)(const void *, const void *)); void twalk (const void *root, void (action) (const void *nodep, const VISIT which, const int depth__));

  1. ifdef _GNU_SOURCE

typedef void (*free_fn_t) (void *nodep); void tdestroy (void *root, free_fn_t free_content__);

  1. endif



tsearch, tfind, twalk, and tdelete manage a binary tree. They are generalized from Knuth (6.2.2) Algorithm T. The first field in each node of the tree is a pointer to the corresponding data item. (The calling program must store the actual data.) compar points to a comparison routine, which takes pointers to two items. It should return an integer which is negative, zero, or positive, depending on whether the first item is less than, equal to, or greater than the second.

tsearch searches the tree for an item. key points to the item to be searched for. rootp points to a variable which points to the root of the tree. If the tree is empty, then the variable that rootp points to should be set to NULL. If the item is found in the tree, then tsearch returns a pointer to it. If it is not found, then tsearch adds it, and returns a pointer to the newly added item.

tfind is like tsearch, except that if the item is not found, then tfind returns NULL.

tdelete deletes an item from the tree. Its arguments are the same as for tsearch.

twalk performs depth-first, left-to-right traversal of a binary tree. root points to the starting node for the traversal. If that node is not the root, then only part of the tree will be visited. twalk calls the user function action each time a node is visited (that is, three times for an internal node, and once for a leaf). action, in turn, takes three arguments. The first is a pointer to the node being visited. The second is an integer which takes on the values preorder, postorder, and endorder depending on whether this is the first, second, or third visit to the internal node, or leaf if it is the single visit to a leaf node. (These symbols are defined in .) The third argument is the depth of the node, with zero being the root. You should not modify the tree while traversing it as the the results would be undefined.

tdestroy() removes the whole tree pointed to by rootp, freeing all resources allocated by the tsearch() function. For the data in each tree node the function free_content is called. The pointer to the data is passed as the argument to the function. If no such work is necessary free_content must point to a function doing nothing. It is called in any case.


tsearch returns a pointer to a matching item in the tree, or to the newly added item, or NULL if there was insufficient memory to add the item. tfind returns a pointer to the item, or NULL if no match is found. If there are multiple elements that match the key, the element returned is unspecified.

tdelete returns a pointer to the parent of the item deleted, or NULL if the item was not found.

tsearch, tfind, and tdelete also return NULL if rootp was NULL on entry.


twalk takes a pointer to the root, while the other functions take a pointer to a variable which points to the root.

twalk uses postorder to mean __

tdelete frees the memory required for the node in the tree. The user is responsible for freeing the memory for the corresponding data.

The example program depends on the fact that twalk makes no further reference to a node after calling the user function with argument __


The following program inserts twelve random numbers into a binary tree, then prints the numbers in order. Note that this example will collapse duplicate numbers.

  1. include



The tdestroy() function is a GNU extension, and it's only defined when the symbol _GNU_SOURCE is defined before including .


qsort(3), bsearch(3), hsearch(3), lsearch(3)

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