用 C 编写的代码的递归到迭代转换

如何解决用 C 编写的代码的递归到迭代转换

这是在 C 中打印 xml 树的代码。如何迭代地编写它？

static void
print_element_names(xmlNode *a_node)
{
    xmlNode *cur_node = NULL;

    for (cur_node = a_node; cur_node; cur_node = cur_node->next) {
        if (cur_node->type == XML_ELEMENT_NODE) {
            printf("node type: Element,name: %s\n",cur_node->name);
        }
        print_element_names(cur_node->children);
    }
}

解决方法

您可以利用 libxml2 中使用的 parent 结构中的 xmlNode 节点：

typedef struct _xmlNode xmlNode;
struct _xmlNode {
    void *_private;              // application data
    xmlElementType type;         // type number,must be second !
    const xmlChar *name;         // the name of the node,or the entity
    struct _xmlNode *children;   // parent->childs link
    struct _xmlNode *last;       // last child link
    struct _xmlNode *parent;     // child->parent link
    struct _xmlNode *next;       // next sibling link
    struct _xmlNode *prev;       // previous sibling link
    struct _xmlDoc *doc;         // the containing document End of common p
    xmlNs *ns;                   // pointer to the associated namespace
    xmlChar *content;            // the content
    struct _xmlAttr *properties; // properties list
    xmlNs *nsDef;                // namespace definitions on this node
    void *psvi;                  // for type/PSVI informations
    unsigned short line;         // line number
    unsigned short extra;        // extra data for XPath/XSLT
};

这是一个非递归版本：

static void print_element_names(xmlNode *a_node) {
    if (a_node != NULL) {
        xmlNode *stop = a_node->parent;
        xmlNode *cur_node = a_node;
        int skip = 0;

        for (;;) {
            if (!skip) {
                if (cur_node->type == XML_ELEMENT_NODE) {
                    printf("node type: Element,name: %s\n",cur_node->name);
                }
                if (cur_node->children) {
                    cur_node = cur_node->children;
                    continue;
                }
            }
            if (cur_node->next) {
                cur_node = cur_node->next;
                skip = 0;
            } else {
                cur_node = cur_node->parent;
                if (cur_node == stop)
                    break;
                skip = 1;
            }
        }
    }
}

,

在 libxml2 的上下文中，这是处理前序和后序遍历的一般方法。正如@chqrlie 所指出的，libxml2 存储一个指向父节点的指针，因此您可以使用常量内存迭代子树。

typedef void
(*callbackFn)(xmlNode *cur,void *data);

void
iterateSubtree(xmlNode *cur,callbackFn callbackPreorder,callbackFn callbackPostorder,void *data) {
    xmlNode *orig;

    if (!cur)
        return;

    orig = cur;
    do {
        callbackPreorder(cur,data);

        while (cur->children) {
            cur = cur->children;
            callbackPreorder(cur,data);
        }

        while (cur != orig) {
            // Storing a copy of next and parent allows the postorder
            // callback to append to or delete a node.
            xmlNode *next = cur->next;
            xmlNode *parent = cur->parent;

            callbackPostorder(cur,data);

            if (next) {
                cur = next;
                break;
            }
            cur = parent;
        }
    } while (cur != orig);

    callbackPostorder(cur,data);
}