[英]why do I get NULL pointers with tinyXML2 in C++?
我是XML解析商务的新手。 非常抱歉提出愚蠢的问题。
我想浏览我的XML:
<?xml version="1.0"?>
<catalog>
<book id="bk101">
<author>Gambardella, Matthew</author>
<title>XML Developer's Guide</title>
<genre>Computer</genre>
<price>44.95</price>
<publish_date>2000-10-01</publish_date>
<description>An in-depth look at creating applications
with XML.</description>
</book>
<book id="bk102">
<author>Ralls, Kim</author>
<title>Midnight Rain</title>
<genre>Fantasy</genre>
<price>5.95</price>
<publish_date>2000-12-16</publish_date>
<description>A former architect battles corporate zombies,
an evil sorceress, and her own childhood to become queen
of the world.</description>
</book>
<book id="bk103">
<author>Corets, Eva</author>
<title>Maeve Ascendant</title>
<genre>Fantasy</genre>
<price>5.95</price>
<publish_date>2000-11-17</publish_date>
<description>After the collapse of a nanotechnology
society in England, the young survivors lay the
foundation for a new society.</description>
</book>
<book id="bk104">
<author>Corets, Eva</author>
<title>Oberon's Legacy</title>
<genre>Fantasy</genre>
<price>5.95</price>
<publish_date>2001-03-10</publish_date>
<description>In post-apocalypse England, the mysterious
agent known only as Oberon helps to create a new life
for the inhabitants of London. Sequel to Maeve
Ascendant.</description>
</book>
<book id="bk105">
<author>Corets, Eva</author>
<title>The Sundered Grail</title>
<genre>Fantasy</genre>
<price>5.95</price>
<publish_date>2001-09-10</publish_date>
<description>The two daughters of Maeve, half-sisters,
battle one another for control of England. Sequel to
Oberon's Legacy.</description>
</book>
<book id="bk106">
<author>Randall, Cynthia</author>
<title>Lover Birds</title>
<genre>Romance</genre>
<price>4.95</price>
<publish_date>2000-09-02</publish_date>
<description>When Carla meets Paul at an ornithology
conference, tempers fly as feathers get ruffled.</description>
</book>
<book id="bk107">
<author>Thurman, Paula</author>
<title>Splish Splash</title>
<genre>Romance</genre>
<price>4.95</price>
<publish_date>2000-11-02</publish_date>
<description>A deep sea diver finds true love twenty
thousand leagues beneath the sea.</description>
</book>
<book id="bk108">
<author>Knorr, Stefan</author>
<title>Creepy Crawlies</title>
<genre>Horror</genre>
<price>4.95</price>
<publish_date>2000-12-06</publish_date>
<description>An anthology of horror stories about roaches,
centipedes, scorpions and other insects.</description>
</book>
</catalog>
而我正在尝试运行的代码(在互联网教程之后)是:
tinyxml2::XMLDocument mappedxml1;
XMLError eResult = mappedxml1.LoadFile(filename1);
if(eResult == XML_SUCCESS){
printf("XMLERROR is %d\nXML loading successfull.\n",eResult);
}
else{
printf("XMLERROR is %d\nXML loading unsuccessfull.\n",eResult);
}
XMLNode * pRoot1 = mappedxml1.FirstChild();
if(pRoot1 == NULL){printf("ERROR: NO ROOT\n");}
else{printf("Good pointer\n");}
XMLElement * pbook1 = pRoot1->FirstChildElement("book id");
if (pbook1 == NULL){printf("ERROR PARSING ELEMENT\n");}
else{printf("GOT IT\n");}
虽然pRoot1
是好走,价值pbook1
始终是NULL
。 我希望它指向bk101
有什么帮助或建议吗? 先感谢您
您正在尝试查找名为book id
的元素。 没有这样的元素。
但是,名称book
有一些元素!
(每个都有一个名为id
的属性 。)
您还需要解析器跳过XML声明 ,该声明当前被FirstChild
调用捕获(因此*pRoot1
不是您认为的!)。 您可以在那里尝试FirstChildElement("catalog")
。
顺便说一句,我建议您检查一下错误处理过程。 目前,如果pRoot1
是空指针,那么您将一条消息写入控制台,然后愉快地继续尝试取消引用该空指针。
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