diff -r 13068743197f -r 2672a2f79484 src/tree.c
--- a/src/tree.c	Mon Feb 19 22:08:09 2024 +0100
+++ b/src/tree.c	Mon Feb 19 22:09:16 2024 +0100
@@ -178,9 +178,50 @@
 
 static void cx_tree_iter_next(void *it) {
     struct cx_tree_iterator_s *iter = it;
+    off_t const loc_next = iter->loc_next;
+    off_t const loc_children = iter->loc_children;
+
     // TODO: support mutating iterator
+    // TODO: support visit_on_exit
 
-    // TODO: implement
+    void *children = tree_children(iter->node);
+    if (children == NULL) {
+        // search for the next node
+        void *current = iter->node;
+        do {
+            // check if there is a sibling
+            void *next = tree_next(current);
+            if (next == NULL) {
+                // no sibling, check again for parent node
+                --iter->depth;
+                if (iter->depth == 0) {
+                    // there is no parent - we have iterated the entire tree
+                    // invalidate the iterator and free the node stack
+                    iter->node = NULL;
+                    current = NULL;
+                    iter->stack_capacity = 0;
+                    free(iter->stack);
+                    iter->stack = NULL;
+                } else {
+                    // the parent node can be obtained from the top of stack
+                    // this way we can avoid the loc_parent in the iterator
+                    current = iter->stack[iter->depth - 1];
+                }
+            } else {
+                // move to the sibling and break the loop
+                current = NULL;
+                iter->counter++;
+                iter->node = next;
+                // new top of stack is the sibling
+                iter->stack[iter->depth - 1] = next;
+            }
+        } while (current != NULL);
+    } else {
+        // node has children, push the first child onto the stack and enter it
+        cx_array_simple_add(iter->stack, children);
+        iter->node = children;
+        iter->counter++;
+    }
 }
 
 CxTreeIterator cx_tree_iterator(