[libxml2 xpath]如何使用字符串查询属性同时包含单引号和双引号 [英] [Libxml2 xpath] how to query a attribute with a string contains single quote and double quotation marks at same time

问题描述

xml示例，lang属性同时包含单引号和双引号

 <？  xml     version   =  1.0    encoding   =  UTF-8 ？ >  
 <   test  >  
 <   node     lang   =  ' 字    /  >  
 <   / test  >  

我的尝试：



我写了一个C程序，但它提示我

XPath错误：无效谓词

/ / node [@lang =''word']

  / *   
 gcc -g`xml2-config --cflags` test.c`xml2-config --libs` 
 * /  
 
  #include   <   libxml / xmlmemory.h  >  
   #include   <   libxml / parser.h  >  
   #include   <   libxml / xpath.h  >  
  
  #define XML_FILE_PATHtest.xml
  
  int  main（ void ）
 {
 xmlDocPtr doc = NULL; 
 xmlXPathObjectPtr object = NULL; 
 xmlXPathContextPtr context = NULL; 
 xmlNodePtr curr = NULL; 
 xmlNodeSetPtr pNodeSet = NULL; 
 xmlChar * prop = NULL; 
  char  lang [] =  '\\ \\word; 
  char  xpath [ 256 ]; 
 
 doc = xmlParseFile（XML_FILE_PATH）; 
  if （NULL == doc）{
 printf（  xmlParseFile failed）; 
  return   -   1 ; 
} 
 context = xmlXPathNewContext（doc）; 
  if （ NULL == context）{
 printf（  xmlXPathNewContext failed）; 
 返回  -   1 ; 
} 
 
  / *  创建对象* /  
 snprintf（xpath， sizeof （XPA th），  // node [@lang ='％s']，lang）; 
 object = xmlXPathEvalExpression（（xmlChar *）xpath，context）; 
 xmlXPathFreeContext（context）; 
  if （object == NULL）{
 printf（  xmlXPathEvalExpression（％s）失败，xpath）; 
 返回  -   1 ; 
} 
 
  / *   NodeSet是空的？ * /  
  if （xmlXPathNodeSetIsEmpty（object-> nodesetval））{
 xmlXPathFreeObject（object）; 
 printf（  xmlXPathNodeSetIsEmpty）; 
  return   0 ; 
} 
 
 pNodeSet = object-> nodesetval; 
 curr = pNodeSet-> nodeTab [ 0 ]; 
 
 prop = xmlGetProp（curr，（xmlChar *）  lang） ; 
 printf（  xmlGetProp％s，prop）; 
 xmlFree（prop）; 
 xmlXPathFreeObject（object）; 
 xmlFreeDoc（doc）; 
 
  return   0 ; 
} 

解决方案

您必须使用字符引用或实体（ XML和HTML字符实体引用列表 - 维基百科 [ ^ ]。



在您的情况下，它将是：

 char lang [] =&& quot; word; 

您还可以编写一个函数来执行此操作：

 //或者使用boost :: replace_all 
 void replace_all（std :: string& str，const std :: string& search，const std :: string& replace）
 {
 size_t len = search.length（）; 
 size_t pos = str.find（search）; 
 while（std :: string :: npos！= npos）
 {
 str.replace（pos，len，replace）; 
 pos = str.find（search，pos + len）; 
} 
} 
 
 void Xmlify（std :: string& str）
 {
 replace_all（str，&，& amp; ;）; //必须是第一个
 replace_all（str，<，& lt;）; 
 replace_all（str，>，& gt;）; 
 replace_all（str，\，& quot;）; 
 replace_all（str，'，& quot;）; 
} 

The xml example, the lang attribute contains single quote and double quotation marks at same time

<?xml version="1.0" encoding="UTF-8"?>
<test>
	<node lang="'"word" />
</test>

What I have tried:

I write a C program, but it prompt me that
XPath error : Invalid predicate
//node[@lang=''"word']

/*
gcc -g `xml2-config --cflags` test.c `xml2-config --libs`
*/

#include <libxml/xmlmemory.h>
#include <libxml/parser.h>
#include <libxml/xpath.h>

#define XML_FILE_PATH "test.xml"

int main(void)
{
	xmlDocPtr doc = NULL;
	xmlXPathObjectPtr object = NULL;
	xmlXPathContextPtr context = NULL;
	xmlNodePtr curr = NULL;
	xmlNodeSetPtr pNodeSet = NULL;
	xmlChar* prop = NULL;
	char lang[] = "'\"word";
	char xpath[256];

	doc = xmlParseFile(XML_FILE_PATH);
	if (NULL == doc) {
		printf("xmlParseFile failed");
		return -1;
	}
	context = xmlXPathNewContext(doc);
	if (NULL == context) {
		printf("xmlXPathNewContext failed");
		return -1;
	}
	
	/* Create Object */
	snprintf(xpath, sizeof(xpath), "//node[@lang='%s']", lang);
	object = xmlXPathEvalExpression((xmlChar*)xpath, context);
	xmlXPathFreeContext(context);
	if (object == NULL) {
		printf("xmlXPathEvalExpression (%s) failed", xpath);
		return -1;
	}
	
	/* NodeSet Is Empty ? */
	if(xmlXPathNodeSetIsEmpty(object->nodesetval)) {
		xmlXPathFreeObject(object);
		printf("xmlXPathNodeSetIsEmpty");
		return 0;
	}

	pNodeSet = object->nodesetval;
	curr = pNodeSet->nodeTab[0];

	prop = xmlGetProp(curr, (xmlChar *)"lang");
	printf("xmlGetProp %s", prop);
	xmlFree(prop);
	xmlXPathFreeObject(object);
	xmlFreeDoc(doc);

	return 0;
}

解决方案

You have to use character references or entities (List of XML and HTML character entity references - Wikipedia[^]).

In your case it would be:

char lang[] = "'"word";

You can also write a function to do that:

// Or use boost::replace_all
void replace_all(std::string& str, const std::string& search, const std::string& replace)
{
    size_t len = search.length();
    size_t pos = str.find(search);
    while (std::string::npos != npos)
    {
        str.replace(pos, len, replace);
        pos = str.find(search, pos + len);
    }
}

void Xmlify(std::string& str)
{
    replace_all(str, "&", "&"); // Must be the first
    replace_all(str, "<", "&lt;");
    replace_all(str, ">", "&gt;");
    replace_all(str, "\"", "&quot;");
    replace_all(str, "'", "&apos;");
}

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