swift libxml2 生成 XML字符串

近来项目需要，生成XML字符串，又不想拼接和用别的三方库，然后就各种搜索百度和ai,记录一下

        let doc = xmlNewDoc(XML_DEFAULT_VERSION)
        //创建根节点 label
        let rootNode = xmlNewNode(nil, "label")!
        xmlDocSetRootElement(doc, rootNode)
        //创建子节点
       let headerNode = xmlNewChild(rootNode, nil, "header", nil)
        xmlNewChild(headerNode, nil, "ModelId", header.ModelId)
        //获取XML字符串
        //https://stackoverflow.com/questions/4155730/creating-string-with-libxml2-c
        var buffer: UnsafeMutablePointer<xmlChar>?
        var size: Int32 = 0
        xmlDocDumpFormatMemoryEnc(doc, &buffer, &size, "UTF-8", 0) //format 0 无格式， 1 带格式
        let xmlString = String(cString: UnsafePointer(buffer!))
        print(xmlString)
        
        xmlFree(buffer)
        xmlFreeDoc(doc)

参考：
creating string with libxml2 c