--- title: Mini-XML 3.3 Programming Manual author: Michael R Sweet copyright: Copyright © 2003-2022, All Rights Reserved. version: 3.3 ... # Introduction Mini-XML is a small XML parsing library that you can use to read XML data files or strings in your application without requiring large non-standard libraries. Mini-XML provides the following functionality: - Reading of UTF-8 and UTF-16 and writing of UTF-8 encoded XML files and strings. - Data is stored in a linked-list tree structure, preserving the XML data hierarchy. - SAX (streamed) reading of XML files and strings to minimize memory usage. - Supports arbitrary element names, attributes, and attribute values with no preset limits, just available memory. - Supports integer, real, opaque ("cdata"), and text data types in "leaf" nodes. - Functions for creating and managing trees of data. - "Find" and "walk" functions for easily locating and navigating trees of data. Mini-XML doesn't do validation or other types of processing on the data based upon schema files or other sources of definition information. ## History Mini-XML was initially developed for the [Gutenprint](http://gutenprint.sf.net/) 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 produced 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 4,300 lines of code, compared to 196,141 lines of code for libxml2 version 2.9.9. ## Resources The Mini-XML home page can be found at . From there you can download the current version of Mini-XML, access the issue tracker, and find other resources. ## Legal Stuff The Mini-XML library is copyright © 2003-2021 by Michael R Sweet and is provided under the Apache License Version 2.0 with an 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 The Mini-XML library is included with your program using the `-lmxml` option: gcc -o myprogram myprogram.c -lmxml 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 mxml` -o myprogram myprogram.c `pkg-config --libs mxml` ## Loading an XML File You load an XML file using the `mxmlLoadFile` function: mxml_node_t * mxmlLoadFile(mxml_node_t *top, FILE *fp, mxml_type_t (*cb)(mxml_node_t *)); The `cb` argument specifies a function that assigns child (value) node types for each element in the document. The callback can be a function you provide or one of the standard functions provided with Mini-XML. For example, to load the XML file "filename.xml" containing text strings you can use the `MXML_OPAQUE_CALLBACK` function: FILE *fp; mxml_node_t *tree; fp = fopen("filename.xml", "r"); tree = mxmlLoadFile(NULL, fp, MXML_OPAQUE_CALLBACK); fclose(fp); Mini-XML also provides functions to load from a file descriptor or string: mxml_node_t * mxmlLoadFd(mxml_node_t *top, int fd, mxml_type_t (*cb)(mxml_node_t *)); mxml_node_t * mxmlLoadString(mxml_node_t *top, const char *s, mxml_type_t (*cb)(mxml_node_t *)); ### Load Callbacks The last argument to the `mxmlLoad` functions is a callback function which is used to determine the value type of each data node in an XML document. Mini-XML defines several standard callbacks for simple XML data files: - `MXML_INTEGER_CALLBACK`: All data nodes contain whitespace-separated integers. - `MXML_OPAQUE_CALLBACK`: All data nodes contain opaque strings with whitespace preserved. - `MXML_REAL_CALLBACK` - All data nodes contain whitespace-separated floating-point numbers. - `MXML_TEXT_CALLBACK` - All data nodes contain whitespace-separated strings. You can provide your own callback functions for more complex XML documents. Your callback function will receive a pointer to the current element node and must return the value type of the immediate children for that element node: `MXML_CUSTOM`, `MXML_INTEGER`, `MXML_OPAQUE`, `MXML_REAL`, or `MXML_TEXT`. The function is called *after* the element and its attributes have been read, so you can look at the element name, attributes, and attribute values to determine the proper value type to return. The following callback function looks for an attribute named "type" or the element name to determine the value type for its child nodes: mxml_type_t type_cb(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 (!strcmp(type, "integer")) return (MXML_INTEGER); else if (!strcmp(type, "opaque")) return (MXML_OPAQUE); else if (!strcmp(type, "real")) return (MXML_REAL); else return (MXML_TEXT); } To use this callback function, simply use the name when you call any of the load functions: FILE *fp; mxml_node_t *tree; fp = fopen("filename.xml", "r"); tree = mxmlLoadFile(NULL, fp, type_cb); fclose(fp); ## Nodes Every piece of information in an XML file is stored in memory in "nodes". Nodes are defined by the `mxml_node_t` structure. Each node has a typed value, optional user data, a parent node, sibling nodes (previous and next), and potentially child nodes. For example, if you have an XML file like the following: val1 val2 val3 val4 val5 val6 val7 val8 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: mxml_type_t mxmlGetType(mxml_node_t *node); - `MXML_CUSTOM` : A custom value defined by your application, - `MXML_ELEMENT` : An XML element, CDATA, comment, or processing instruction, - `MXML_INTEGER` : A whitespace-delimited integer value, - `MXML_OPAQUE` : An opaque string value that preserves all whitespace, - `MXML_REAL` : A whitespace-delimited floating point value, or - `MXML_TEXT` : A whitespace-delimited text (fragment) value. > Note: CDATA, comment, and processing directive nodes are currently stored in > memory as special elements. This will be changed in a future major release of > Mini-XML. The parent and sibling nodes are accessed using the `mxmlGetParent`, `mxmlGetNextSibling`, and `mxmlGetPreviousSibling` functions, while the children of an element node are accessed using the `mxmlGetFirstChild` or `mxmlGetLastChild` functions: mxml_node_t * mxmlGetFirstChild(mxml_node_t *node); mxml_node_t * mxmlGetLastChild(mxml_node_t *node); mxml_node_t * mxmlGetNextSibling(mxml_node_t *node); mxml_node_t * mxmlGetParent(mxml_node_t *node); mxml_node_t * mxmlGetPrevSibling(mxml_node_t *node); The `mxmlGetUserData` function gets any user (application) data associated with the node: void * mxmlGetUserData(mxml_node_t *node); ## Creating XML Documents You can create and update XML documents in memory using the various `mxmlNew` functions. The following code will create the XML document described in the previous section: mxml_node_t *xml; /* */ mxml_node_t *data; /* */ mxml_node_t *node; /* */ mxml_node_t *group; /* */ xml = mxmlNewXML("1.0"); data = mxmlNewElement(xml, "data"); node = mxmlNewElement(data, "node"); mxmlNewText(node, 0, "val1"); node = mxmlNewElement(data, "node"); mxmlNewText(node, 0, "val2"); node = mxmlNewElement(data, "node"); mxmlNewText(node, 0, "val3"); group = mxmlNewElement(data, "group"); node = mxmlNewElement(group, "node"); mxmlNewText(node, 0, "val4"); node = mxmlNewElement(group, "node"); mxmlNewText(node, 0, "val5"); node = mxmlNewElement(group, "node"); mxmlNewText(node, 0, "val6"); node = mxmlNewElement(data, "node"); mxmlNewText(node, 0, "val7"); node = mxmlNewElement(data, "node"); mxmlNewText(node, 0, "val8"); We start by creating the declaration node common to all XML files using the `mxmlNewXML` function: xml = mxmlNewXML("1.0"); We then create the `` 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 `...` 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 - 0 or false in this case. The last argument specifies the actual text to add: node = mxmlNewElement(data, "node"); mxmlNewText(node, 0, "val1"); The resulting in-memory XML document can then be saved or processed just like one loaded from disk or a string. ## Saving an XML File You save an XML file using the `mxmlSaveFile` function: int mxmlSaveFile(mxml_node_t *node, FILE *fp, mxml_save_cb_t cb); The `cb` argument specifies a function that returns the whitespace (if any) that is inserted before and after each element node. The `MXML_NO_CALLBACK` constant tells Mini-XML to not include any extra whitespace. For example, so save an XML file to the file "filename.xml" with no extra whitespace: FILE *fp; fp = fopen("filename.xml", "w"); mxmlSaveFile(xml, fp, MXML_NO_CALLBACK); fclose(fp); Mini-XML also provides functions to save to a file descriptor or strings: char * mxmlSaveAllocString(mxml_node_t *node, mxml_save_cb_t cb); int mxmlSaveFd(mxml_node_t *node, int fd, mxml_save_cb_t cb); int mxmlSaveString(mxml_node_t *node, char *buffer, int bufsize, mxml_save_cb_t cb); ### Controlling Line Wrapping When saving XML documents, Mini-XML normally wraps output lines at column 75 so that the text is readable in terminal windows. The `mxmlSetWrapMargin` function overrides the default wrap margin for the current thread: void mxmlSetWrapMargin(int column); For example, the following code sets the margin to 132 columns: mxmlSetWrapMargin(132); while the following code disables wrapping by setting the margin to 0: mxmlSetWrapMargin(0); ### Save Callbacks The last argument to the `mxmlSave` functions is a callback function which is used to automatically insert whitespace in an XML document. Your callback function will be called up to four times for each element node with a pointer to the node and a "where" value of `MXML_WS_BEFORE_OPEN`, `MXML_WS_AFTER_OPEN`, `MXML_WS_BEFORE_CLOSE`, or `MXML_WS_AFTER_CLOSE`. The callback function should return `NULL` if no whitespace should be added or the string to insert (spaces, tabs, carriage returns, and newlines) 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(mxml_node_t *node, int 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
  • 's,
    's, and
    '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); } To use this callback function, simply use the name when you call any of the save functions: FILE *fp; mxml_node_t *tree; fp = fopen("filename.xml", "w"); mxmlSaveFile(tree, fp, whitespace_cb); fclose(fp); ## Memory Management Once you are done with the XML data, use the `mxmlDelete` function to recursively free the memory that is used for a particular node or the entire tree: void mxmlDelete(mxml_node_t *tree); You can also use reference counting to manage memory usage. The `mxmlRetain` and `mxmlRelease` functions increment and decrement a node's use count, respectively. When the use count goes to zero, `mxmlRelease` automatically calls `mxmlDelete` to actually free the memory used by the node tree. New nodes start with a use count of 1. # More About Nodes ## Element Nodes Element \(`MXML_ELEMENT`) nodes are created using the `mxmlNewElement` function. Element attributes are set using the `mxmlElementSetAttr` and `mxmlElementSetAttrf` functions and cleared using the `mxmlElementDeleteAttr` function: mxml_node_t * mxmlNewElement(mxml_node_t *parent, const char *name); void mxmlElementDeleteAttr(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, ...); Child nodes are added using the various `mxmlNew` functions. The top (root) node must be an element, usually created by the `mxmlNewXML` function: mxml_node_t * mxmlNewXML(const char *version); The `mxmlGetElement` function retrieves the element name, the `mxmlElementGetAttr` function retrieves the value string for a named attribute associated with the element. The `mxmlElementGetAttrByIndex` and `mxmlElementGetAttrCount` functions retrieve attributes by index: const char * mxmlGetElement(mxml_node_t *node); const char * mxmlElementGetAttr(mxml_node_t *node, const char *name); const char * mxmlElementGetAttrByIndex(mxml_node_t *node, int idx, const char **name); int mxmlElementGetAttrCount(mxml_node_t *node); ## CDATA Nodes CDATA \(`MXML_ELEMENT`) nodes are created using the `mxmlNewCDATA` function: mxml_node_t *mxmlNewCDATA(mxml_node_t *parent, const char *string); The `mxmlGetCDATA` function retrieves the CDATA string pointer for a node: const char *mxmlGetCDATA(mxml_node_t *node); ## Comment Nodes Because comments are currently stored as element nodes, comment \(`MXML_ELEMENT`) nodes are created using the `mxmlNewElement` function by including the surrounding "!--" and "--" characters in the element name, for example: mxml_node_t *node = mxmlNewElement("!-- This is a comment --"); Similarly, the `mxmlGetElement` function retrieves the comment string pointer for a node, which includes the surrounding "!--" and "--" characters. const char *comment = mxmlGetElement(node); /* returns "!-- This is a comment --" */ ## Processing Instruction Nodes Because processing instructions are currently stored as element nodes, processing instruction \(`MXML_ELEMENT`) nodes are created using the `mxmlNewElement` function including the surrounding "?" characters: mxml_node_t *node = mxmlNewElement("?xml-stylesheet type=\"text/css\" href=\"style.css\"?"); The `mxmlGetElement` function retrieves the processing instruction string for a node, including the surrounding "?" characters: const char *instr = mxmlGetElement(node); /* returned "?xml-stylesheet type=\"text/css\" href=\"style.css\"?" */ ## Integer Nodes Integer \(`MXML_INTEGER`) nodes are created using the `mxmlNewInteger` function: mxml_node_t * mxmlNewInteger(mxml_node_t *parent, int integer); The `mxmlGetInteger` function retrieves the integer value for a node: int mxmlGetInteger(mxml_node_t *node); ## Opaque String Nodes Opaque string \(`MXML_OPAQUE`) nodes are created using the `mxmlNewOpaque` function: mxml_node_t * mxmlNewOpaque(mxml_node_t *parent, const char *opaque); The `mxmlGetOpaque` function retrieves the opaque string pointer for a node: const char * mxmlGetOpaque(mxml_node_t *node); ## Text Nodes Whitespace-delimited text string \(`MXML_TEXT`) nodes are created using the `mxmlNewText` and `mxmlNewTextf` functions. Each text node consists of a text string and (leading) whitespace flag value. mxml_node_t * mxmlNewText(mxml_node_t *parent, int whitespace, const char *string); mxml_node_t * mxmlNewTextf(mxml_node_t *parent, int whitespace, const char *format, ...); The `mxmlGetText` function retrieves the text string pointer and whitespace flag value for a node: const char * mxmlGetText(mxml_node_t *node, int *whitespace); ## Real Number Nodes Real number \(`MXML_REAL`) nodes are created using the `mxmlNewReal` function: mxml_node_t * mxmlNewReal(mxml_node_t *parent, double real); The `mxmlGetReal` function retrieves the real number for a node: double mxmlGetReal(mxml_node_t *node); # Locating Data in an XML Document Mini-XML provides many functions for enumerating, searching, and indexing XML documents. ## Finding Nodes The `mxmlFindPath` function finds the (first) value node under a specific element using a "path": mxml_node_t * mxmlFindPath(mxml_node_t *node, const char *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 *value = mxmlFindPath(xml, "data/group/node"); mxml_node_t *value = 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.: /* Find the first "a" element */ node = mxmlFindElement(tree, tree, "a", NULL, NULL, MXML_DESCEND); /* Find the first "a" element with "href" attribute */ node = mxmlFindElement(tree, tree, "a", "href", NULL, MXML_DESCEND); /* Find the first "a" element with "href" to a URL */ node = mxmlFindElement(tree, tree, "a", "href", "http://michaelrsweet.github.io/", MXML_DESCEND); /* Find the first element with a "src" attribute*/ node = mxmlFindElement(tree, tree, NULL, "src", NULL, MXML_DESCEND); /* Find the first element with a "src" = "foo.jpg" */ node = mxmlFindElement(tree, tree, NULL, "src", "foo.jpg", MXML_DESCEND); You can also iterate with the same function: mxml_node_t *node; for (node = mxmlFindElement(tree, tree, "element", NULL, NULL, MXML_DESCEND); node != NULL; node = mxmlFindElement(node, tree, "element", NULL, NULL, MXML_DESCEND)) { ... do something ... } The `descend` argument \(`MXML_DESCEND` in the examples above) can be one of three constants: - `MXML_NO_DESCEND`: 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`: search child nodes first, then sibling nodes, and then parent nodes. ## 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 previous section: mxml_node_t *node; for (node = xml; node != NULL; node = mxmlWalkNext(node, xml, MXML_DESCEND)) { ... do something ... } The nodes will be returned in the following order: val1 val2 val3 val4 val5 val6 val7 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: int mxmlIndexGetCount(mxml_index_t *ind); Finally, the `mxmlIndexDelete` function frees all memory associated with the index: void mxmlIndexDelete(mxml_index_t *ind); # Custom Data Types Mini-XML supports custom data types via per-thread load and save callbacks. Only a single set of callbacks can be active at any time for the current thread, however your callbacks can store additional information in order to support multiple custom data types as needed. The `MXML_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_CUSTOM`) nodes are created using the `mxmlNewCustom` function or using a custom per-thread load callbacks specified using the `mxmlSetCustomHandlers` function: typedef void (*mxml_custom_destroy_cb_t)(void *); typedef int (*mxml_custom_load_cb_t)(mxml_node_t *, const char *); typedef char *(*mxml_custom_save_cb_t)(mxml_node_t *); mxml_node_t * mxmlNewCustom(mxml_node_t *parent, void *data, mxml_custom_destroy_cb_t destroy); int mxmlSetCustom(mxml_node_t *node, void *data, mxml_custom_destroy_cb_t destroy); void mxmlSetCustomHandlers(mxml_custom_load_cb_t load, mxml_custom_save_cb_t save); The load callback receives 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 format), the load callback would look like the following: typedef struct { unsigned year, /* Year */ month, /* Month */ day, /* Day */ hour, /* Hour */ minute, /* Minute */ second; /* Second */ time_t unix; /* UNIX time */ } iso_date_time_t; int load_custom(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 (-1); } /* * 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 (-1); } /* * 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 destroy (free) function * pointers... */ mxmlSetCustom(node, data, free); /* * Return with no errors... */ return (0); } The function itself can return 0 on success or -1 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 * save_custom(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 the callback functions using the `mxmlSetCustomHandlers` function: mxmlSetCustomHandlers(load_custom, save_custom); # 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 `mxmlSAXLoadFd`, `mxmlSAXLoadFile`, and `mxmlSAXLoadString` functions provide the SAX loading APIs: mxml_node_t * mxmlSAXLoadFd(mxml_node_t *top, int fd, mxml_type_t (*cb)(mxml_node_t *), mxml_sax_cb_t sax, void *sax_data); mxml_node_t * mxmlSAXLoadFile(mxml_node_t *top, FILE *fp, mxml_type_t (*cb)(mxml_node_t *), mxml_sax_cb_t sax, void *sax_data); mxml_node_t * mxmlSAXLoadString(mxml_node_t *top, const char *s, mxml_type_t (*cb)(mxml_node_t *), mxml_sax_cb_t sax, void *sax_data); Each function works like the corresponding `mxmlLoad` function but uses a callback to process each node as it is read. The callback function receives the node, an event code, and a user data pointer you supply: void sax_cb(mxml_node_t *node, mxml_sax_event_t event, void *data) { ... do something ... } The event will be one of the following: - `MXML_SAX_CDATA`: CDATA was just read. - `MXML_SAX_COMMENT`: A comment was just read. - `MXML_SAX_DATA`: Data (custom, integer, opaque, real, or text) was just read. - `MXML_SAX_DIRECTIVE`: A processing directive/instruction was just read. - `MXML_SAX_ELEMENT_CLOSE` - A close element was just read \(``) - `MXML_SAX_ELEMENT_OPEN` - An open element was just read \(``) 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: void sax_cb(mxml_node_t *node, mxml_sax_event_t event, void *data) { if (event != MXML_SAX_ELEMENT_CLOSE) mxmlRetain(node); } 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 ``, ``, and ``, and processing directives like `` and ``: void sax_cb(mxml_node_t *node, mxml_sax_event_t event, void *data) { 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_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); } } } The resulting skeleton document tree can then be searched just like one loaded using the `mxmlLoad` functions. 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_node_t *doc, *title, *body, *heading; doc = mxmlSAXLoadFd(NULL, 0, MXML_TEXT_CALLBACK, sax_cb, NULL); title = mxmlFindElement(doc, doc, "title", NULL, NULL, MXML_DESCEND); if (title) print_children(title); body = mxmlFindElement(doc, doc, "body", NULL, NULL, MXML_DESCEND); if (body) { for (heading = mxmlGetFirstChild(body); heading; heading = mxmlGetNextSibling(heading)) print_children(heading); } The `print_children` function is: void print_children(mxml_node_t *parent) { mxml_node_t *node; const char *text; int whitespace; for (node = mxmlGetFirstChild(parent); node != NULL; node = mxmlGetNextSibling(node)) { text = mxmlGetText(node, &whitespace); if (whitespace) putchar(' '); fputs(text, stdout); } putchar('\n'); }