Daniel Veillard | c948420 | 2001-10-24 12:35:52 +0000 | [diff] [blame] | 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd"> |
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| 12 | <title>A real example</title> |
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| 17 | <a href="http://www.gnome.org/"><img src="smallfootonly.gif" alt="Gnome Logo"></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo"></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo"></a> |
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| 20 | <h1>The XML C library for Gnome</h1> |
| 21 | <h2>A real example</h2> |
| 22 | </td></tr></table></td></tr></table></td> |
| 23 | </tr></table> |
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Daniel Veillard | 594cf0b | 2001-10-25 08:09:12 +0000 | [diff] [blame^] | 25 | <td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td> |
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Daniel Veillard | c948420 | 2001-10-24 12:35:52 +0000 | [diff] [blame] | 27 | <tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr> |
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Daniel Veillard | 594cf0b | 2001-10-25 08:09:12 +0000 | [diff] [blame^] | 54 | <li> |
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Daniel Veillard | c948420 | 2001-10-24 12:35:52 +0000 | [diff] [blame] | 57 | </ul></td></tr> |
Daniel Veillard | 594cf0b | 2001-10-25 08:09:12 +0000 | [diff] [blame^] | 58 | </table> |
| 59 | <table width="100%" border="0" cellspacing="1" cellpadding="3"> |
| 60 | <tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr> |
| 61 | <tr><td bgcolor="#fffacd"><ul style="margin-left: -2pt"> |
| 62 | <li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li> |
| 63 | <li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li> |
| 64 | <li><a href="http://www.cs.unibo.it/~casarini/gdome2/">DOM gdome2</a></li> |
| 65 | <li><a href="ftp://xmlsoft.org/">FTP</a></li> |
| 66 | <li><a href="http://www.fh-frankfurt.de/~igor/projects/libxml/">Windows binaries</a></li> |
| 67 | <li><a href="http://pages.eidosnet.co.uk/~garypen/libxml/">Solaris binaries</a></li> |
| 68 | </ul></td></tr> |
| 69 | </table> |
| 70 | </td></tr></table></td> |
Daniel Veillard | c948420 | 2001-10-24 12:35:52 +0000 | [diff] [blame] | 71 | <td valign="top" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd"> |
| 72 | <p>Here is a real size example, where the actual content of the application |
| 73 | data is not kept in the DOM tree but uses internal structures. It is based on |
| 74 | a proposal to keep a database of jobs related to Gnome, with an XML based |
| 75 | storage structure. Here is an <a href="gjobs.xml">XML encoded jobs |
| 76 | base</a>:</p> |
| 77 | <pre><?xml version="1.0"?> |
| 78 | <gjob:Helping xmlns:gjob="http://www.gnome.org/some-location"> |
| 79 | <gjob:Jobs> |
| 80 | |
| 81 | <gjob:Job> |
| 82 | <gjob:Project ID="3"/> |
| 83 | <gjob:Application>GBackup</gjob:Application> |
| 84 | <gjob:Category>Development</gjob:Category> |
| 85 | |
| 86 | <gjob:Update> |
| 87 | <gjob:Status>Open</gjob:Status> |
| 88 | <gjob:Modified>Mon, 07 Jun 1999 20:27:45 -0400 MET DST</gjob:Modified> |
| 89 | <gjob:Salary>USD 0.00</gjob:Salary> |
| 90 | </gjob:Update> |
| 91 | |
| 92 | <gjob:Developers> |
| 93 | <gjob:Developer> |
| 94 | </gjob:Developer> |
| 95 | </gjob:Developers> |
| 96 | |
| 97 | <gjob:Contact> |
| 98 | <gjob:Person>Nathan Clemons</gjob:Person> |
| 99 | <gjob:Email>nathan@windsofstorm.net</gjob:Email> |
| 100 | <gjob:Company> |
| 101 | </gjob:Company> |
| 102 | <gjob:Organisation> |
| 103 | </gjob:Organisation> |
| 104 | <gjob:Webpage> |
| 105 | </gjob:Webpage> |
| 106 | <gjob:Snailmail> |
| 107 | </gjob:Snailmail> |
| 108 | <gjob:Phone> |
| 109 | </gjob:Phone> |
| 110 | </gjob:Contact> |
| 111 | |
| 112 | <gjob:Requirements> |
| 113 | The program should be released as free software, under the GPL. |
| 114 | </gjob:Requirements> |
| 115 | |
| 116 | <gjob:Skills> |
| 117 | </gjob:Skills> |
| 118 | |
| 119 | <gjob:Details> |
| 120 | A GNOME based system that will allow a superuser to configure |
| 121 | compressed and uncompressed files and/or file systems to be backed |
| 122 | up with a supported media in the system. This should be able to |
| 123 | perform via find commands generating a list of files that are passed |
| 124 | to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine |
| 125 | or via operations performed on the filesystem itself. Email |
| 126 | notification and GUI status display very important. |
| 127 | </gjob:Details> |
| 128 | |
| 129 | </gjob:Job> |
| 130 | |
| 131 | </gjob:Jobs> |
| 132 | </gjob:Helping></pre> |
| 133 | <p>While loading the XML file into an internal DOM tree is a matter of |
| 134 | calling only a couple of functions, browsing the tree to gather the ata and |
| 135 | generate the internal structures is harder, and more error prone.</p> |
| 136 | <p>The suggested principle is to be tolerant with respect to the input |
| 137 | structure. For example, the ordering of the attributes is not significant, |
| 138 | the XML specification is clear about it. It's also usually a good idea not to |
| 139 | depend on the order of the children of a given node, unless it really makes |
| 140 | things harder. Here is some code to parse the information for a person:</p> |
| 141 | <pre>/* |
| 142 | * A person record |
| 143 | */ |
| 144 | typedef struct person { |
| 145 | char *name; |
| 146 | char *email; |
| 147 | char *company; |
| 148 | char *organisation; |
| 149 | char *smail; |
| 150 | char *webPage; |
| 151 | char *phone; |
| 152 | } person, *personPtr; |
| 153 | |
| 154 | /* |
| 155 | * And the code needed to parse it |
| 156 | */ |
| 157 | personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) { |
| 158 | personPtr ret = NULL; |
| 159 | |
| 160 | DEBUG("parsePerson\n"); |
| 161 | /* |
| 162 | * allocate the struct |
| 163 | */ |
| 164 | ret = (personPtr) malloc(sizeof(person)); |
| 165 | if (ret == NULL) { |
| 166 | fprintf(stderr,"out of memory\n"); |
| 167 | return(NULL); |
| 168 | } |
| 169 | memset(ret, 0, sizeof(person)); |
| 170 | |
| 171 | /* We don't care what the top level element name is */ |
| 172 | cur = cur->xmlChildrenNode; |
| 173 | while (cur != NULL) { |
| 174 | if ((!strcmp(cur->name, "Person")) && (cur->ns == ns)) |
| 175 | ret->name = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); |
| 176 | if ((!strcmp(cur->name, "Email")) && (cur->ns == ns)) |
| 177 | ret->email = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); |
| 178 | cur = cur->next; |
| 179 | } |
| 180 | |
| 181 | return(ret); |
| 182 | }</pre> |
| 183 | <p>Here are a couple of things to notice:</p> |
| 184 | <ul> |
| 185 | <li>Usually a recursive parsing style is the more convenient one: XML data |
| 186 | is by nature subject to repetitive constructs and usually exibits highly |
| 187 | stuctured patterns.</li> |
| 188 | <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>, |
| 189 | i.e. the pointer to the global XML document and the namespace reserved to |
| 190 | the application. Document wide information are needed for example to |
| 191 | decode entities and it's a good coding practice to define a namespace for |
| 192 | your application set of data and test that the element and attributes |
| 193 | you're analyzing actually pertains to your application space. This is |
| 194 | done by a simple equality test (cur->ns == ns).</li> |
| 195 | <li>To retrieve text and attributes value, you can use the function |
| 196 | <em>xmlNodeListGetString</em> to gather all the text and entity reference |
| 197 | nodes generated by the DOM output and produce an single text string.</li> |
| 198 | </ul> |
| 199 | <p>Here is another piece of code used to parse another level of the |
| 200 | structure:</p> |
| 201 | <pre>#include <libxml/tree.h> |
| 202 | /* |
| 203 | * a Description for a Job |
| 204 | */ |
| 205 | typedef struct job { |
| 206 | char *projectID; |
| 207 | char *application; |
| 208 | char *category; |
| 209 | personPtr contact; |
| 210 | int nbDevelopers; |
| 211 | personPtr developers[100]; /* using dynamic alloc is left as an exercise */ |
| 212 | } job, *jobPtr; |
| 213 | |
| 214 | /* |
| 215 | * And the code needed to parse it |
| 216 | */ |
| 217 | jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) { |
| 218 | jobPtr ret = NULL; |
| 219 | |
| 220 | DEBUG("parseJob\n"); |
| 221 | /* |
| 222 | * allocate the struct |
| 223 | */ |
| 224 | ret = (jobPtr) malloc(sizeof(job)); |
| 225 | if (ret == NULL) { |
| 226 | fprintf(stderr,"out of memory\n"); |
| 227 | return(NULL); |
| 228 | } |
| 229 | memset(ret, 0, sizeof(job)); |
| 230 | |
| 231 | /* We don't care what the top level element name is */ |
| 232 | cur = cur->xmlChildrenNode; |
| 233 | while (cur != NULL) { |
| 234 | |
| 235 | if ((!strcmp(cur->name, "Project")) && (cur->ns == ns)) { |
| 236 | ret->projectID = xmlGetProp(cur, "ID"); |
| 237 | if (ret->projectID == NULL) { |
| 238 | fprintf(stderr, "Project has no ID\n"); |
| 239 | } |
| 240 | } |
| 241 | if ((!strcmp(cur->name, "Application")) && (cur->ns == ns)) |
| 242 | ret->application = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); |
| 243 | if ((!strcmp(cur->name, "Category")) && (cur->ns == ns)) |
| 244 | ret->category = xmlNodeListGetString(doc, cur->xmlChildrenNode, 1); |
| 245 | if ((!strcmp(cur->name, "Contact")) && (cur->ns == ns)) |
| 246 | ret->contact = parsePerson(doc, ns, cur); |
| 247 | cur = cur->next; |
| 248 | } |
| 249 | |
| 250 | return(ret); |
| 251 | }</pre> |
| 252 | <p>Once you are used to it, writing this kind of code is quite simple, but |
| 253 | boring. Ultimately, it could be possble to write stubbers taking either C |
| 254 | data structure definitions, a set of XML examples or an XML DTD and produce |
| 255 | the code needed to import and export the content between C data and XML |
| 256 | storage. This is left as an exercise to the reader :-)</p> |
| 257 | <p>Feel free to use <a href="example/gjobread.c">the code for the full C |
| 258 | parsing example</a> as a template, it is also available with Makefile in the |
| 259 | Gnome CVS base under gnome-xml/example</p> |
| 260 | <p><a href="mailto:daniel@veillard.com">Daniel Veillard</a></p> |
| 261 | </td></tr></table></td></tr></table></td></tr></table></td> |
| 262 | </tr></table></td></tr></table> |
| 263 | </body> |
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