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Mini-XML was initially developed for the Gutenprint project to replace the rather large and unwieldy libxml2 library with something substantially smaller and easier-to-use. It all began one morning in June of 2003 when Robert posted the following sentence to the developer's list:

It's bad enough that we require libxml2, but rolling our own XML parser is a bit more than we can handle.

I then replied with:

Given the limited scope of what you use in XML, it should be trivial to code a mini-XML API in a few hundred lines of code.

I took my own challenge and coded furiously for two days to produce the initial public release of Mini-XML, total lines of code: 696. Robert promptly integrated Mini-XML into Gutenprint and removed libxml2.

Thanks to lots of feedback and support from various developers, Mini-XML has evolved since then to provide a more complete XML implementation and now stands at a whopping 3,491 lines of code, compared to 175,808 lines of code for libxml2 version 2.11.7.

Resources

The Mini-XML home page can be found at https://www.msweet.org/mxml. From there you can download the current version of Mini-XML, access the issue tracker, and find other resources.

Mini-XML v4 has a slightly different API than prior releases. See the Migrating from Mini-XML v3.x chapter for details.

Legal Stuff

The Mini-XML library is copyright © 2003-2024 by Michael R Sweet and is provided under the Apache License Version 2.0 with an (optional) exception to allow linking against GPL2/LGPL2-only software. See the files "LICENSE" and "NOTICE" for more information.

Using Mini-XML

Mini-XML provides a single header file which you include:

#include <mxml.h>

The Mini-XML library is included with your program using the -lmxml4 option:

gcc -o myprogram myprogram.c -lmxml4

If you have the pkg-config software installed, you can use it to determine the proper compiler and linker options for your installation:

gcc `pkg-config --cflags mxml4` -o myprogram myprogram.c `pkg-config --libs mxml4`

Note: The library name "mxml4" is a configure-time option. If you use the --disable-libmxml4-prefix configure option the library is named "mxml".

API Basics

Every piece of information in an XML file is stored in memory in "nodes". Nodes are represented by mxml_node_t pointers. Each node has an associated type, value(s), a parent node, sibling nodes (previous and next), potentially first and last child nodes, and an optional user data pointer.

For example, if you have an XML file like the following:

<?xml version="1.0" encoding="utf-8"?>
<data>
    <node>val1</node>
    <node>val2</node>
    <node>val3</node>
    <group>
        <node>val4</node>
        <node>val5</node>
        <node>val6</node>
    </group>
    <node>val7</node>
    <node>val8</node>
</data>

the node tree for the file would look like the following in memory:

<?xml version="1.0" encoding="utf-8"?>
  |
<data>
  |
<node> - <node> - <node> - <group> - <node> - <node>
  |        |        |         |        |        |
 val1     val2     val3       |       val7     val8
                              |
                            <node> - <node> - <node>
                              |        |        |
                             val4     val5     val6

where "-" is a pointer to the sibling node and "|" is a pointer to the first child or parent node.

The mxmlGetType function gets the type of a node which is represented as a mxml_type_t enumeration value:

MXML_TYPE_CDATA: CDATA such as <![CDATA[...]]>,
MXML_TYPE_COMMENT: A comment such as ,
MXML_TYPE_CUSTOM: A custom value defined by your application,
MXML_TYPE_DECLARATION: A declaration such as <!DOCTYPE html>,
MXML_TYPE_DIRECTIVE: A processing instruction such as <?xml version="1.0" encoding="utf-8"?>,
MXML_TYPE_ELEMENT: An XML element with optional attributes such as <element name="value">,
MXML_TYPE_INTEGER: A whitespace-delimited integer value such as 42,
MXML_TYPE_OPAQUE: An opaque string value that preserves all whitespace such as All work and no play makes Johnny a dull boy.,
MXML_TYPE_REAL: A whitespace-delimited floating point value such as 123.4, or
MXML_TYPE_TEXT: A whitespace-delimited text (fragment) value such as Word.

The parent, sibling, and child nodes are accessed using the mxmlGetParent, mxmlGetNextSibling, mxmlGetPreviousSibling, mxmlGetFirstChild, and mxmlGetLastChild functions.

The value(s) of a node are accessed using the mxmlGetCDATA, mxmlGetComment, mxmlGetDeclaration, mxmlGetDirective, mxmlGetElement, mxmlElementGetAttr, mxmlGetInteger, mxmlGetOpaque, mxmlGetReal, and mxmlGetText functions.

Loading an XML File

You load an XML file using the mxmlLoadFilename function:

mxml_node_t *
mxmlLoadFilename(mxml_node_t *top, mxml_options_t *options,
                 const char *filename);

Mini-XML also provides functions to load from a FILE pointer, a file descriptor, a string, or using a callback:

mxml_node_t *
mxmlLoadFd(mxml_node_t *top, mxml_options_t *options,
           int fd);

mxml_node_t *
mxmlLoadFile(mxml_node_t *top, mxml_options_t *options,
             FILE *fp);

mxml_node_t *
mxmlLoadIO(mxml_node_t *top, mxml_options_t *options,
           mxml_io_cb_t io_cb, void *io_cbdata);

mxml_node_t *
mxmlLoadString(mxml_node_t *top, mxml_options_t *options,
               const char *s);

Each accepts a pointer to the top-most ("root") node (usually NULL) you want to add the XML data to, any load options, and the content to be loaded. For example, the following code will load an XML file called "example.xml" using the default load options:

mxml_node_t *xml;

xml = mxmlLoadFilename(/*top*/NULL, /*options*/NULL,
                       "example.xml");

Load Options

Load options are specified using a mxml_options_t pointer, which you create using the mxmlOptionsNew function:

mxml_options_t *options = mxmlOptionsNew();

The default load options will treat any values in your XML as whitespace- delimited text (MXML_TYPE_TEXT). You can specify a different type of values using the mxmlOptionsSetTypeValue function. For example, the following will specify that values are opaque text strings, including whitespace (MXML_TYPE_OPAQUE):

mxmlOptionsSetTypeValue(options, MXML_TYPE_OPAQUE);

For more complex XML documents, you can specify a callback that returns the type of value for a given element node using the mxmlOptionsSetTypeCallback function. For example, to specify a callback function called my_type_cb that has no callback data:

mxmlOptionsSetTypeCallback(options, my_type_cb, /*cbdata*/NULL);

The my_type_cb function accepts the callback data pointer (NULL in this case) and the mxml_node_t pointer for the current element and returns a mxml_type_t enumeration value specifying the value type for child nodes. For example, the following function looks at the "type" attribute and the element name to determine the value types of the node's children:

mxml_type_t
my_load_cb(void *cbdata, mxml_node_t *node)
{
  const char *type;

 /*
  * You can lookup attributes and/or use the element name,
  * hierarchy, etc...
  */

  type = mxmlElementGetAttr(node, "type");
  if (type == NULL)
    type = mxmlGetElement(node);
  if (type == NULL)
    type = "text";

  if (!strcmp(type, "integer"))
    return (MXML_TYPE_INTEGER);
  else if (!strcmp(type, "opaque"))
    return (MXML_TYPE_OPAQUE);
  else if (!strcmp(type, "real"))
    return (MXML_TYPE_REAL);
  else
    return (MXML_TYPE_TEXT);
}

Finding Nodes

The mxmlFindPath function finds the (first) value node under a specific element using a path. The path string can contain the "*" wildcard to match a single element node in the hierarchy. For example, the following code will find the first "node" element under the "group" element, first using an explicit path and then using a wildcard:

mxml_node_t *directnode = mxmlFindPath(xml, "data/group/node");

mxml_node_t *wildnode = mxmlFindPath(xml, "data/*/node");

The mxmlFindElement function can be used to find a named element, optionally matching an attribute and value:

mxml_node_t *
mxmlFindElement(mxml_node_t *node, mxml_node_t *top,
                const char *element, const char *attr,
                const char *value, int descend);

The element, attr, and value arguments can be passed as NULL to act as wildcards, e.g.:

mxml_node_t *node;

/* Find the first "a" element */
node = mxmlFindElement(tree, tree, "a", NULL, NULL,
                       MXML_DESCEND_ALL);

/* Find the first "a" element with "href" attribute */
node = mxmlFindElement(tree, tree, "a", "href", NULL,
                       MXML_DESCEND_ALL);

/* Find the first "a" element with "href" to a URL */
node = mxmlFindElement(tree, tree, "a", "href",
                       "http://msweet.org/",
                       MXML_DESCEND_ALL);

/* Find the first element with a "src" attribute*/
node = mxmlFindElement(tree, tree, NULL, "src", NULL,
                       MXML_DESCEND_ALL);

/* Find the first element with a "src" = "foo.jpg" */
node = mxmlFindElement(tree, tree, NULL, "src", "foo.jpg",
                       MXML_DESCEND_ALL);

You can also iterate with the same function:

mxml_node_t *node;

for (node = mxmlFindElement(tree, tree, "element", NULL,
                            NULL, MXML_DESCEND_ALL);
     node != NULL;
     node = mxmlFindElement(node, tree, "element", NULL,
                            NULL, MXML_DESCEND_ALL))
{
  ... do something ...
}

The descend argument (MXML_DESCEND_ALL in the previous examples) can be one of three constants:

MXML_DESCEND_NONE: ignore child nodes in the element hierarchy, instead using siblings (same level) or parent nodes (above) until the top (root) node is reached.
MXML_DESCEND_FIRST: start the search with the first child of the node, and then search siblings. You'll normally use this when iterating through direct children of a parent node, e.g. all of the <node> and <group> elements under the <?xml ...?> parent node in the previous example.
MXML_DESCEND_ALL: search child nodes first, then sibling nodes, and then parent nodes.

Getting the Value(s) from Nodes

Once you have the node you can use one of the mxmlGetXxx functions to retrieve its value(s).

Element (MXML_TYPE_ELEMENT) nodes have an associated name and zero or more named attributes with (string) values. The mxmlGetElement function retrieves the element name while the mxmlElementGetAttr function retrieves the value string for a named attribute. For example, the following code looks for HTML heading elements and, when found, displays the "id" attribute for the heading:

const char *elemname = mxmlGetElement(node);
const char *id_value = mxmlElementGetAttr(node, "id");

if ((*elemname == 'h' || *elemname == 'H') &&
    elemname[1] >= '1' && elemname[1] <= '6' &&
    id_value != NULL)
  printf("%s: %s\n", elemname, id_value);

The mxmlElementGetAttrByIndex and mxmlElementGetAttrCount functions allow you to iterate all attributes of an element. For example, the following code prints the element name and each of its attributes:

const char *elemname = mxmlGetElement(node);
printf("%s:\n", elemname);

size_t i, count;
for (i = 0, count = mxmlElementGetAttrCount(node); i < count; i ++)
{
  const char *attrname, *attrvalue;

  attrvalue = mxmlElementGetAttrByIndex(node, i, &attrname);

  printf("    %s=\"%s\"\n", attrname, attrvalue);
}

CDATA (MXML_TYPE_CDATA) nodes have an associated string value consisting of the text between the <![CDATA[ and ]]> delimiters. The mxmlGetCDATA function retrieves the CDATA string pointer for a node. For example, the following code gets the CDATA string value:

const char *cdatavalue = mxmlGetCDATA(node);

Comment (MXML_TYPE_COMMENT) nodes have an associated string value consisting of the text between the  delimiters. The mxmlGetComment function retrieves the comment string pointer for a node. For example, the following code gets the comment string value:

const char *commentvalue = mxmlGetComment(node);

Processing instruction (MXML_TYPE_DIRECTIVE) nodes have an associated string value consisting of the text between the <? and ?> delimiters. The mxmlGetDirective function retrieves the processing instruction string for a node. For example, the following code gets the processing instruction string value:

const char *instrvalue = mxmlGetDirective(node);

Integer (MXML_TYPE_INTEGER) nodes have an associated long value. The mxmlGetInteger function retrieves the integer value for a node. For example, the following code gets the integer value:

long intvalue = mxmlGetInteger(node);

Opaque string (MXML_TYPE_OPAQUE) nodes have an associated string value consisting of the text between elements. The mxmlGetOpaque function retrieves the opaque string pointer for a node. For example, the following code gets the opaque string value:

const char *opaquevalue = mxmlGetOpaque(node);

Real number (MXML_TYPE_REAL) nodes have an associated double value. The mxmlGetReal function retrieves the real number for a node. For example, the following code gets the real value:

double realvalue = mxmlGetReal(node);

Whitespace-delimited text string (MXML_TYPE_TEXT) nodes have an associated whitespace indicator and string value extracted from the text between elements. The mxmlGetText function retrieves the text string pointer and whitespace boolean value for a node. For example, the following code gets the text and whitespace indicator:

const char *textvalue;
bool whitespace;

textvalue = mxmlGetText(node, &whitespace);

Saving an XML File

You save an XML file using the mxmlSaveFilename function:

bool
mxmlSaveFilename(mxml_node_t *node, mxml_options_t *options,
                 const char *filename);

Mini-XML also provides functions to save to a FILE pointer, a file descriptor, a string, or using a callback:

char *
mxmlSaveAllocString(mxml_node_t *node, mxml_options_t *options);

bool
mxmlSaveFd(mxml_node_t *node, mxml_options_t *options,
           int fd);

bool
mxmlSaveFile(mxml_node_t *node, mxml_options_t *options,
             FILE *fp);

bool
mxmlSaveIO(mxml_node_t *node, mxml_options_t *options,
           mxml_io_cb_t *io_cb, void *io_cbdata);

size_t
mxmlSaveString(mxml_node_t *node, mxml_options_t *options,
               char *buffer, size_t bufsize);

Each accepts a pointer to the top-most ("root") node, any save options, and (as needed) the destination. For example, the following code saves an XML file to the file "example.xml" with the default options:

mxmlSaveFile(xml, /*options*/NULL, "example.xml");

Save Options

Save options are specified using a mxml_options_t pointer, which you create using the mxmlOptionsNew function:

mxml_options_t *options = mxmlOptionsNew();

The default save options will wrap output lines at column 72 but not add any additional whitespace otherwise. You can change the wrap column using the mxmlOptionsSetWrapMargin function. For example, the following will set the wrap column to 0 which disables wrapping:

mxmlOptionsSetWrapMargin(options, 0);

To add additional whitespace to the output, set a whitespace callback using the mxmlOptionsSetWhitespaceCallback function. A whitespace callback accepts a callback data pointer, the current node, and a whitespace position value of MXML_WS_BEFORE_OPEN, MXML_WS_AFTER_OPEN, MXML_WS_BEFORE_CLOSE, or MXML_WS_AFTER_CLOSE. The callback should return NULL if no whitespace is to be inserted or a string of spaces, tabs, carriage returns, and newlines to insert otherwise.

The following whitespace callback can be used to add whitespace to XHTML output to make it more readable in a standard text editor:

const char *
whitespace_cb(void *cbdata, mxml_node_t *node, mxml_ws_t where)
{
  const char *element;

 /*
  * We can conditionally break to a new line before or after
  * any element.  These are just common HTML elements...
  */

  element = mxmlGetElement(node);

  if (!strcmp(element, "html") ||
      !strcmp(element, "head") ||
      !strcmp(element, "body") ||
      !strcmp(element, "pre") ||
      !strcmp(element, "p") ||
      !strcmp(element, "h1") ||
      !strcmp(element, "h2") ||
      !strcmp(element, "h3") ||
      !strcmp(element, "h4") ||
      !strcmp(element, "h5") ||
      !strcmp(element, "h6"))
  {
   /*
    * Newlines before open and after close...
    */

    if (where == MXML_WS_BEFORE_OPEN ||
        where == MXML_WS_AFTER_CLOSE)
      return ("\n");
  }
  else if (!strcmp(element, "dl") ||
           !strcmp(element, "ol") ||
           !strcmp(element, "ul"))
  {
   /*
    * Put a newline before and after list elements...
    */

    return ("\n");
  }
  else if (!strcmp(element, "dd") ||
           !strcmp(element, "dt") ||
           !strcmp(element, "li"))
  {
   /*
    * Put a tab before <li>'s, <dd>'s, and <dt>'s, and a
    * newline after them...
    */

    if (where == MXML_WS_BEFORE_OPEN)
      return ("\t");
    else if (where == MXML_WS_AFTER_CLOSE)
      return ("\n");
  }

 /*
  * Otherwise return NULL for no added whitespace...
  */

  return (NULL);
}

The following code will set the whitespace callback for the save options:

mxmlOptionsSetWhitespaceCallback(options, whitespace_cb, /*cbdata*/NULL);

Freeing Memory

Once you are done with the XML data, use the mxmlDelete function to free the memory that is used for a particular node and its children. For example, the following code frees the XML data loaded by the previous examples:

mxmlDelete(xml);

Creating New XML Documents

You can create new and update existing XML documents in memory using the various mxmlNewXxx functions. The following code will create the XML document described in the Using Mini-XML chapter:

mxml_node_t *xml;    /* <?xml version="1.0" charset="utf-8"?> */
mxml_node_t *data;   /* <data> */
mxml_node_t *node;   /* <node> */
mxml_node_t *group;  /* <group> */

xml = mxmlNewXML("1.0");

data = mxmlNewElement(xml, "data");

  node = mxmlNewElement(data, "node");
  mxmlNewText(node, false, "val1");
  node = mxmlNewElement(data, "node");
  mxmlNewText(node, false, "val2");
  node = mxmlNewElement(data, "node");
  mxmlNewText(node, false, "val3");

  group = mxmlNewElement(data, "group");

    node = mxmlNewElement(group, "node");
    mxmlNewText(node, false, "val4");
    node = mxmlNewElement(group, "node");
    mxmlNewText(node, false, "val5");
    node = mxmlNewElement(group, "node");
    mxmlNewText(node, false, "val6");

  node = mxmlNewElement(data, "node");
  mxmlNewText(node, false, "val7");
  node = mxmlNewElement(data, "node");
  mxmlNewText(node, false, "val8");

We start by creating the processing instruction node common to all XML files using the mxmlNewXML function:

xml = mxmlNewXML("1.0");

We then create the <data> node used for this document using the mxmlNewElement function. The first argument specifies the parent node (xml) while the second specifies the element name (data):

data = mxmlNewElement(xml, "data");

Each <node>...</node> in the file is created using the mxmlNewElement and mxmlNewText functions. The first argument of mxmlNewText specifies the parent node (node). The second argument specifies whether whitespace appears before the text - false in this case. The last argument specifies the actual text to add:

node = mxmlNewElement(data, "node");
mxmlNewText(node, false, "val1");

The resulting in-memory XML document can then be saved or processed just like one loaded from disk or a string.

Element Nodes

Element (MXML_TYPE_ELEMENT) nodes are created using the mxmlNewElement function. Element attributes are set using the mxmlElementSetAttr and mxmlElementSetAttrf functions and cleared using the mxmlElementClearAttr function:

mxml_node_t *
mxmlNewElement(mxml_node_t *parent, const char *name);

void
mxmlElementClearAttr(mxml_node_t *node, const char *name);

void
mxmlElementSetAttr(mxml_node_t *node, const char *name,
                   const char *value);

void
mxmlElementSetAttrf(mxml_node_t *node, const char *name,
                    const char *format, ...);

CDATA Nodes

CDATA (MXML_TYPE_CDATA) nodes are created using the mxmlNewCDATA and mxmlNewCDATAf functions and set using the mxmlSetCDATA and mxmlSetCDATAf functions:

mxml_node_t *
mxmlNewCDATA(mxml_node_t *parent, const char *string);

mxml_node_t *
mxmlNewCDATAf(mxml_node_t *parent, const char *format, ...);

void
mxmlSetCDATA(mxml_node_t *node, const char *string);

void
mxmlSetCDATAf(mxml_node_t *node, const char *format, ...);

Comment Nodes

Comment (MXML_TYPE_COMMENT) nodes are created using the mxmlNewComment and mxmlNewCommentf functions and set using the mxmlSetComment and mxmlSetCommentf functions:

mxml_node_t *
mxmlNewComment(mxml_node_t *parent, const char *string);

mxml_node_t *
mxmlNewCommentf(mxml_node_t *parent, const char *format, ...);

void
mxmlSetComment(mxml_node_t *node, const char *string);

void
mxmlSetCommentf(mxml_node_t *node, const char *format, ...);

Processing Instruction Nodes

Processing instruction (MXML_TYPE_DIRECTIVE) nodes are created using the mxmlNewDirective and mxmlNewDirectivef functions and set using the mxmlSetDirective and mxmlSetDirectivef functions:

mxml_node_t *node = mxmlNewDirective("xml-stylesheet type=\"text/css\" href=\"style.css\"");

mxml_node_t *node = mxmlNewDirectivef("xml version=\"%s\"", version);

The mxmlNewXML function can be used to create the top-level "xml" processing instruction with an associated version number:

mxml_node_t *
mxmlNewXML(const char *version);

Integer Nodes

Integer (MXML_TYPE_INTEGER) nodes are created using the mxmlNewInteger function and set using the mxmlSetInteger function:

mxml_node_t *
mxmlNewInteger(mxml_node_t *parent, long integer);

void
mxmlSetInteger(mxml_node_t *node, long integer);

Opaque String Nodes

Opaque string (MXML_TYPE_OPAQUE) nodes are created using the mxmlNewOpaque and mxmlNewOpaquef functions and set using the mxmlSetOpaque and mxmlSetOpaquef functions:

mxml_node_t *
mxmlNewOpaque(mxml_node_t *parent, const char *opaque);

mxml_node_t *
mxmlNewOpaquef(mxml_node_t *parent, const char *format, ...);

void
mxmlSetOpaque(mxml_node_t *node, const char *opaque);

void
mxmlSetOpaquef(mxml_node_t *node, const char *format, ...);

Real Number Nodes

Real number (MXML_TYPE_REAL) nodes are created using the mxmlNewReal function and set using the mxmlSetReal function:

mxml_node_t *
mxmlNewReal(mxml_node_t *parent, double real);

void
mxmlSetReal(mxml_node_t *node, double real);

Text Nodes

Whitespace-delimited text string (MXML_TYPE_TEXT) nodes are created using the mxmlNewText and mxmlNewTextf functions and set using the mxmlSetText and mxmlSetTextf functions. Each text node consists of a text string and (leading) whitespace boolean value.

mxml_node_t *
mxmlNewText(mxml_node_t *parent, bool whitespace,
            const char *string);

mxml_node_t *
mxmlNewTextf(mxml_node_t *parent, bool whitespace,
             const char *format, ...);

void
mxmlSetText(mxml_node_t *node, bool whitespace,
            const char *string);

void
mxmlSetTextf(mxml_node_t *node, bool whitespace,
             const char *format, ...);

Iterating and Indexing the Tree

Iterating Nodes

While the mxmlFindNode and mxmlFindPath functions will find a particular element node, sometimes you need to iterate over all nodes. The mxmlWalkNext and mxmlWalkPrev functions can be used to iterate through the XML node tree:

mxml_node_t *
mxmlWalkNext(mxml_node_t *node, mxml_node_t *top,
             int descend);

mxml_node_t *
mxmlWalkPrev(mxml_node_t *node, mxml_node_t *top,
             int descend);

Depending on the value of the descend argument, these functions will automatically traverse child, sibling, and parent nodes until the top node is reached. For example, the following code will iterate over all of the nodes in the sample XML document in the Using Mini-XML chapter:

mxml_node_t *node;

for (node = xml;
     node != NULL;
     node = mxmlWalkNext(node, xml, MXML_DESCEND_ALL))
{
  ... do something ...
}

The nodes will be returned in the following order:

<?xml version="1.0" encoding="utf-8"?>
<data>
<node>
val1
<node>
val2
<node>
val3
<group>
<node>
val4
<node>
val5
<node>
val6
<node>
val7
<node>
val8

Indexing

The mxmlIndexNew function allows you to create an index of nodes for faster searching and enumeration:

mxml_index_t *
mxmlIndexNew(mxml_node_t *node, const char *element,
             const char *attr);

The element and attr arguments control which elements are included in the index. If element is not NULL then only elements with the specified name are added to the index. Similarly, if attr is not NULL then only elements containing the specified attribute are added to the index. The nodes are sorted in the index.

For example, the following code creates an index of all "id" values in an XML document:

mxml_index_t *ind = mxmlIndexNew(xml, NULL, "id");

Once the index is created, the mxmlIndexFind function can be used to find a matching node:

mxml_node_t *
mxmlIndexFind(mxml_index_t *ind, const char *element,
              const char *value);

For example, the following code will find the element whose "id" string is "42":

mxml_node_t *node = mxmlIndexFind(ind, NULL, "42");

Alternately, the mxmlIndexReset and mxmlIndexEnum functions can be used to enumerate the nodes in the index:

mxml_node_t *
mxmlIndexReset(mxml_index_t *ind);

mxml_node_t *
mxmlIndexEnum(mxml_index_t *ind);

Typically these functions will be used in a for loop:

mxml_node_t *node;

for (node = mxmlIndexReset(ind);
     node != NULL;
     node = mxmlIndexEnum(ind))
{
  ... do something ...
}

The mxmlIndexCount function returns the number of nodes in the index:

size_t
mxmlIndexGetCount(mxml_index_t *ind);

Finally, the mxmlIndexDelete function frees all memory associated with the index:

void
mxmlIndexDelete(mxml_index_t *ind);

Advanced Usage

Custom Data Types

Mini-XML supports custom data types via load and save callback options. Only a single set of callbacks can be active at any time for a mxml_options_t pointer, however your callbacks can store additional information in order to support multiple custom data types as needed. The MXML_TYPE_CUSTOM node type identifies custom data nodes.

The mxmlGetCustom function retrieves the custom value pointer for a node.

const void *
mxmlGetCustom(mxml_node_t *node);

Custom (MXML_TYPE_CUSTOM) nodes are created using the mxmlNewCustom function or using the custom load callback specified using the mxmlOptionsSetCustomCallbacks function:

typedef void (*mxml_custfree_cb_t)(void *cbdata, void *data);
typedef bool (*mxml_custload_cb_t)(void *cbdata, mxml_node_t *, const char *);
typedef char *(*mxml_custsave_cb_t)(void *cbdata, mxml_node_t *);

mxml_node_t *
mxmlNewCustom(mxml_node_t *parent, void *data,
              mxml_custfree_cb_t free_cb, void *free_cbdata);

int
mxmlSetCustom(mxml_node_t *node, void *data,
              mxml_custfree_cb_t free_cb, void *free_cbdata);

void
mxmlOptionsSetCustomCallbacks(mxml_option_t *options,
                              mxml_custload_cb_t load_cb,
                              mxml_custsave_cb_t save_cb,
                              void *cbdata);

The load callback receives the callback data pointer, a pointer to the current data node, and a string of opaque character data from the XML source with character entities converted to the corresponding UTF-8 characters. For example, if we wanted to support a custom date/time type whose value is encoded as "yyyy-mm-ddThh:mm:ssZ" (ISO 8601 format), the load callback would look like the following:

typedef struct iso_date_time_s
{
  unsigned year,    /* Year */
           month,   /* Month */
           day,     /* Day */
           hour,    /* Hour */
           minute,  /* Minute */
           second;  /* Second */
  time_t   unix;    /* UNIX time */
} iso_date_time_t;

bool
custom_load_cb(void *cbdata, mxml_node_t *node, const char *data)
{
  iso_date_time_t *dt;
  struct tm tmdata;

 /*
  * Allocate data structure...
  */

  dt = calloc(1, sizeof(iso_date_time_t));

 /*
  * Try reading 6 unsigned integers from the data string...
  */

  if (sscanf(data, "%u-%u-%uT%u:%u:%uZ", &(dt->year),
             &(dt->month), &(dt->day), &(dt->hour),
             &(dt->minute), &(dt->second)) != 6)
  {
   /*
    * Unable to read numbers, free the data structure and
    * return an error...
    */

    free(dt);

    return (false);
  }

 /*
  * Range check values...
  */

  if (dt->month < 1 || dt->month > 12 ||
      dt->day < 1 || dt->day > 31 ||
      dt->hour < 0 || dt->hour > 23 ||
      dt->minute < 0 || dt->minute > 59 ||
      dt->second < 0 || dt->second > 60)
  {
   /*
    * Date information is out of range...
    */

    free(dt);

    return (false);
  }

 /*
  * Convert ISO time to UNIX time in seconds...
  */

  tmdata.tm_year = dt->year - 1900;
  tmdata.tm_mon  = dt->month - 1;
  tmdata.tm_day  = dt->day;
  tmdata.tm_hour = dt->hour;
  tmdata.tm_min  = dt->minute;
  tmdata.tm_sec  = dt->second;

  dt->unix = gmtime(&tmdata);

 /*
  * Assign custom node data and free callback function/data...
  */

  mxmlSetCustom(node, data, custom_free_cb, cbdata);

 /*
  * Return with no errors...
  */

  return (true);
}

The function itself can return true on success or false if it is unable to decode the custom data or the data contains an error. Custom data nodes contain a void pointer to the allocated custom data for the node and a pointer to a destructor function which will free the custom data when the node is deleted. In this example, we use the standard free function since everything is contained in a single calloc'd block.

The save callback receives the node pointer and returns an allocated string containing the custom data value. The following save callback could be used for our ISO date/time type:

char *
custom_save_cb(void *cbdata, mxml_node_t *node)
{
  char data[255];
  iso_date_time_t *dt;


  dt = (iso_date_time_t *)mxmlGetCustom(node);

  snprintf(data, sizeof(data),
           "%04u-%02u-%02uT%02u:%02u:%02uZ",
           dt->year, dt->month, dt->day, dt->hour,
           dt->minute, dt->second);

  return (strdup(data));
}

You register these callback functions using the mxmlOptionsSetCustomCallbacks function:

mxmlOptionsSetCustomCallbacks(options, custom_load_cb,
                              custom_save_cb, /*cbdata*/NULL);

SAX (Stream) Loading of Documents

Mini-XML supports an implementation of the Simple API for XML (SAX) which allows you to load and process an XML document as a stream of nodes. Aside from allowing you to process XML documents of any size, the Mini-XML implementation also allows you to retain portions of the document in memory for later processing.

The mxmlLoadXxx functions support a SAX option that is enabled by setting a callback function and data pointer with the mxmlOptionsSetSAXCallback function. The callback function receives the data pointer you supplied, the node, and an event code and returns true to continue processing or false to stop:

bool
sax_cb(void *cbdata, mxml_node_t *node,
       mxml_sax_event_t event)
{
  ... do something ...

  // Continue processing...
  return (true);
}

The event will be one of the following:

MXML_SAX_EVENT_CDATA: CDATA was just read.
MXML_SAX_EVENT_COMMENT: A comment was just read.
MXML_SAX_EVENT_DATA: Data (integer, opaque, real, or text) was just read.
MXML_SAX_EVENT_DECLARATION: A declaration was just read.
MXML_SAX_EVENT_DIRECTIVE: A processing directive/instruction was just read.
MXML_SAX_EVENT_ELEMENT_CLOSE - A close element was just read (</element>)
MXML_SAX_EVENT_ELEMENT_OPEN - An open element was just read (<element>)

Elements are released after the close element is processed. All other nodes are released after they are processed. The SAX callback can retain the node using the mxmlRetain function. For example, the following SAX callback will retain all nodes, effectively simulating a normal in-memory load:

bool
sax_cb(void *cbdata, mxml_node_t *node, mxml_sax_event_t event)
{
  if (event != MXML_SAX_ELEMENT_CLOSE)
    mxmlRetain(node);

  return (true);
}

More typically the SAX callback will only retain a small portion of the document that is needed for post-processing. For example, the following SAX callback will retain the title and headings in an XHTML file. It also retains the (parent) elements like <html>, <head>, and <body>, and processing directives like <?xml ... ?> and declarations like <!DOCTYPE ... >:

bool
sax_cb(void *cbdata, mxml_node_t *node,
       mxml_sax_event_t event)
{
  if (event == MXML_SAX_ELEMENT_OPEN)
  {
   /*
    * Retain headings and titles...
    */

    const char *element = mxmlGetElement(node);

    if (!strcmp(element, "html") ||
        !strcmp(element, "head") ||
        !strcmp(element, "title") ||
        !strcmp(element, "body") ||
        !strcmp(element, "h1") ||
        !strcmp(element, "h2") ||
        !strcmp(element, "h3") ||
        !strcmp(element, "h4") ||
        !strcmp(element, "h5") ||
        !strcmp(element, "h6"))
      mxmlRetain(node);
  }
  else if (event == MXML_SAX_DECLARATION)
    mxmlRetain(node);
  else if (event == MXML_SAX_DIRECTIVE)
    mxmlRetain(node);
  else if (event == MXML_SAX_DATA)
  {
    if (mxmlGetRefCount(mxmlGetParent(node)) > 1)
    {
     /*
      * If the parent was retained, then retain this data
      * node as well.
      */

      mxmlRetain(node);
    }
  }

  return (true);
}

The resulting skeleton document tree can then be searched just like one loaded without the SAX callback function. For example, a filter that reads an XHTML document from stdin and then shows the title and headings in the document would look like:

mxml_options_t *options;
mxml_node_t *xml, *title, *body, *heading;

options = mxmlOptionsNew();
mxmlOptionsSetSAXCallback(options, sax_cb,
                          /*cbdata*/NULL);

xml = mxmlLoadFd(/*top*/NULL, options, /*fd*/0);

title = mxmlFindElement(doc, doc, "title", NULL, NULL,
                        MXML_DESCEND_ALL);

if (title)
  print_children(title);

body = mxmlFindElement(doc, doc, "body", NULL, NULL,
                       MXML_DESCEND_ALL);

if (body)
{
  for (heading = mxmlGetFirstChild(body);
       heading;
       heading = mxmlGetNextSibling(heading))
    print_children(heading);
}

mxmlDelete(xml);
mxmlOptionsDelete(options);

The print_children function is:

void
print_children(mxml_node_t *parent)
{
  mxml_node_t *node;
  const char *text;
  bool whitespace;

  for (node = mxmlGetFirstChild(parent);
       node != NULL;
       node = mxmlGetNextSibling(node))
  {
    text = mxmlGetText(node, &whitespace);

    if (whitespace)
      putchar(' ');

    fputs(text, stdout);
  }

  putchar('\n');
}

User Data

Each node has an associated user data pointer that can be used to store useful information for your application. The memory used by the data pointer is not managed by Mini-XML so it is up to you to free it as necessary.

The mxmlSetUserData function sets any user (application) data associated with the node while the mxmlGetUserData function gets any user (application) data associated with the node:

void *
mxmlGetUserData(mxml_node_t *node);

void
mxmlSetUserData(mxml_node_t *node, void *user_data);

Memory Management

Nodes support reference counting to manage memory usage. The mxmlRetain and mxmlRelease functions increment and decrement a node's reference count, respectively. When the reference count goes to zero, mxmlRelease calls mxmlDelete to actually free the memory used by the node tree. New nodes start with a reference count of 1. You can get a node's current reference count using the mxmlGetRefCount function.

Strings can also support different kinds of memory management. The default is to use the standard C library strdup and free functions. To use alternate an alternate mechanism, call the mxmlSetStringCallbacks function to set string copy and free callbacks. The copy callback receives the callback data pointer and the string to copy, and returns a new string that will persist for the life of the XML data. The free callback receives the callback data pointer and the copied string and potentially frees the memory used for it. For example, the following code implements a simple string pool that eliminates duplicate strings:

typedef struct string_pool_s
{
  size_t num_strings;   // Number of strings
  size_t alloc_strings; // Allocated strings
  char   **strings;      // Array of strings
} string_pool_t;

char *
copy_string(string_pool_t *pool, const char *s)
{
  size_t i;     // Looping var
  char   *news; // Copy of string


  // See if the string is already in the pool...
  for (i = 0; i < pool->num_strings; i ++)
  {
    if (!strcmp(pool->strings[i], s))
      return (pool->strings[i]);
  }

  // Not in the pool, add new string
  if (pool->num_strings >= pool->alloc_strings)
  {
    // Expand the string pool...
    char **temp; // New strings array

    temp = realloc(pool->strings,
                   (pool->alloc_strings + 32) *
                       sizeof(char *));

    if (temp == NULL)
      return (NULL);

    pool->alloc_strings += 32;
    pool->strings = temp;
  }

  if ((news = strdup(s)) != NULL)
    pool->strings[pool->num_strings ++] = news;

  return (news);
}

void
free_string(string_pool_t *pool, char *s)
{
  // Do nothing here...
}

void
free_all_strings(string_pool_t *pool)
{
  size_t i; // Looping var


  for (i = 0; i < pool->num_strings; i ++)
    free(pool->strings[i]);
  free(pool->strings);
}

...

// Setup the string pool...
string_pool_t pool = { 0, 0, NULL };

mxmlSetStringCallbacks((mxml_strcopy_cb_t)copy_string,
                       (mxml_strfree_cb_t)free_string,
                       &pool);

// Load an XML file...
mxml_node_t *xml;

xml = mxmlLoadFilename(/*top*/NULL, /*options*/NULL,
                       "example.xml");

// Process the XML file...
...

// Free memory used by the XML file...
mxmlDelete(xml);

// Free all strings in the pool...
free_all_strings(&pool);

Migrating from Mini-XML v3.x

The following incompatible API changes were made in Mini-XML v4.0:

Load and save callbacks and options are now managed using mxml_options_t values.
The mxmlSAXLoadXxx functions have been removed in favor of setting the SAX callback function and data pointers of the mxml_options_t value prior to calling the corresponding mxmlLoadXxx functions.
SAX events are now named MXML_SAX_EVENT_foo instead of MXML_SAX_foo.
SAX callbacks now return a boolean value.
Node types are now named MXML_TYPE_foo instead of MXML_foo.
Descend values are now normalized to MXML_DESCEND_ALL, MXML_DESCEND_FIRST, and MXML_DESCEND_NONE.
Functions that returned 0 on success and -1 on error now return true on success and false on error.
CDATA nodes ("<![CDATA[...]]>") now have their own type (MXML_TYPE_CDATA).
Comment nodes ("") now have their own type (MXML_TYPE_COMMENT).
Declaration nodes ("<!...>") now have their own type (MXML_TYPE_DECLARATION).
Element attributes are now cleared with the mxmlElementClearAttr function instead of mxmlElementDeleteAttr.
Processing instruction/directive nodes ("<?...?>") now have their own type (MXML_TYPE_DIRECTIVE).
Integer nodes (MXML_TYPE_INTEGER) now use the long type.
Text nodes (MXML_TYPE_TEXT) now use the bool type for the whitespace value.
Custom node callbacks are now set using the mxmlOptionsSetCustomCallbacks function instead of the thread-global mxmlSetCustomHandlers function.

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