Expat+SCEW-操弄XML的瑞士刀

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本文介绍如何利用Expat+SCEW工具库轻松读写XML文件。通过简单的API即可实现创建复杂的XML结构及解析，适用于各种XML处理场景。

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Expat+SCEW-操弄XML的瑞士刀

作者: Joey 日期: 2008-09-04 18:38

字体大小: 小中大

之前处理XML文件时,就是用这套工具横行江湖,Expat提供细致的函式读写xml文件,SCEW则是把Expat函式包装成亮丽的界面供使用者更方便的存取xml,个人觉的,这两套函式库实在不输给.net System.xml下的API

首先下载expat library和scew library ,这两套软体的使用方式很简单,执行configure,make,make install后,就可以使用它们的library,而我这边的范例编译时用static link,所以我都直接连接它们的.a函式库档

Makefile的范例如下

ALL : example
example : example . c
$ ( CC ) - I ./ scew - 0.4.0 / scew / - o example example . c libscew . a libexpat . a
clean :
rm example

SCEW write xml的方法大概就五组API如下
(1)创造xml tree: tree = scew_tree_create();
(2)加入root element: scew_tree_add_root(scew_tree*, char*);
(3)加入root element的子element: scew_element_add(scew_element*,char*);
(4)加入element attribute: scew_element_add_attr_pair(scew_element*, char*, char*);;
(5)加入element content: scew_element_set_contents(scew_element*, char *);

写入xml文件的范例如下

int CreateXML ()
{
scew_tree * tree = NULL ;
scew_element * root = NULL ;
scew_element * element = NULL ;
scew_element * sub_element = NULL ;
scew_element * sub_sub_element = NULL ;
scew_attribute * attribute = NULL ;
tree = scew_tree_create () ;
root = scew_tree_add_root ( tree , " scew_test " ) ;
/* Add an element and set element contents. */
element = scew_element_add ( root , " element1 " ) ;
scew_element_set_contents ( element , " element contents. " ) ;
/* Add an element with an attribute pair (name, value). */
element = scew_element_add ( root , " element2 " ) ;
scew_element_add_attr_pair ( element , " attribute " , " value " ) ;
element = scew_element_add ( root , " element3 " ) ;
scew_element_add_attr_pair ( element , " attribute1 " , " value1 " ) ;
/**
* Another way to add an attribute. You loose attribute ownership,
* so there is no need to free it.
*/
attribute = scew_attribute_create ( " attribute2 " , " value2 " ) ;
scew_element_add_attr ( element , attribute ) ;
element = scew_element_add ( root , " element4 " ) ;
sub_element = scew_element_add ( element , " sub_element1 " ) ;
scew_element_add_attr_pair ( sub_element , " attribute " , " value " ) ;
sub_element = scew_element_add ( element , " sub_element2 " ) ;
scew_element_add_attr_pair ( sub_element , " attribute1 " , " value1 " ) ;
scew_element_add_attr_pair ( sub_element , " attribute2 " , " value2 " ) ;
sub_sub_element = scew_element_add ( sub_element , " sub_sub_element1 " ) ;
scew_element_add_attr_pair ( sub_sub_element , " attribute1 " , " value1 " ) ;
scew_element_add_attr_pair ( sub_sub_element , " attribute2 " , " value2 " ) ;
scew_element_add_attr_pair ( sub_sub_element , " attribute3 " , " value3 " ) ;
/* Check attribute2 replacement. */
scew_element_add_attr_pair ( sub_sub_element , " attribute2 " , " new_value2 " ) ;
scew_element_set_contents ( sub_sub_element , " element contents. " ) ;
scew_writer_tree_file ( tree , " example.xml " ) ;
scew_tree_free ( tree ) ;
return 0 ;
}

执行范例会制造出如下内容的xml

<? xml version = " 1.0 " encoding = " UTF-8 " standalone = " no " ?>
< scew_test >
< element1 > element contents .</ element1 >
< element2 attribute = " value " />
< element3 attribute1 = " value1 " attribute2 = " value2 " />
< element4 >
< sub_element1 attribute = " value " />
< sub_element2 attribute1 = " value1 " attribute2 = " value2 " >
< sub_sub_element1 attribute1 = " value1 " attribute2 = " new_value2 " attribute3 = " value3 " > element contents .</ sub_sub_element1 >
</ sub_element2 >
</ element4 >
</ scew_test >

而SCEW读取xml的方法大约有6组API
(1)创造xml parser: parser = scew_parser_create;
(2)读入xml档案: scew_parser_load_file(scew_parser*,char*)
(3)读出element name: scew_element_name(scew_element*)
(4)读出element attribute: scew_attribute_next(scew_element*, scew_attribute*)
(5)读出element content: scew_element_contents(scew_element*)
(6)寻找子element: scew_element_next(scew_element*, scew_element*)

读取xml文件的范例如下

void print_attributes ( scew_element * element )
{
scew_attribute * attribute = NULL ;
if ( element != NULL )
{
/**
* Iterates through the element's attribute list, printing the
* pair name-value.
*/
attribute = NULL ;
while (( attribute = scew_attribute_next ( element , attribute )) != NULL )
printf ( " %s= \ " % s \ "" , scew_attribute_name ( attribute ) , scew_attribute_value ( attribute )) ;
}
}
int PrintElement ( scew_element * element )
{
scew_element * child = NULL ;
XML_Char const * contents = NULL ;
printf ( " element name: %s " , scew_element_name ( element )) ;
print_attributes ( element ) ;
contents = scew_element_contents ( element ) ;
if ( contents == NULL )
printf ( " \ n \ n " ) ;
else printf ( " \ n%s content:%s \ n \ n " , scew_element_name ( element ) , contents ) ;
/**
* Call print_element function again for each child of the
* current element.
*/
while (( child = scew_element_next ( element , child )) != NULL )
PrintElement ( child ) ;
return 0 ;
}
int ReadXML ()
{
scew_tree * tree = NULL ;
scew_parser * parser = NULL ;
scew_element * element = NULL ,* parent = NULL ;
/**
* Creates an SCEW parser. This is the first function to call.
*/
parser = scew_parser_create () ;
scew_parser_ignore_whitespaces ( parser , 1 ) ;
if ( ! scew_parser_load_file ( parser , " example.xml " )) return 0 ;
tree = scew_parser_tree ( parser ) ;
PrintElement ( scew_tree_root ( tree )) ; //traverse all child and siblings of tree
/* Remember to free tree (scew_parser_free does not free it) */
scew_tree_free ( tree ) ;
/* Frees the SCEW parser */
scew_parser_free ( parser ) ;
return 0 ;