## Simple XML Subset Parser

Simple XML Subset Parser — parses a subset of XML

## Synopsis

    #include <glib.h>

    enum                GMarkupError;
    #define             G_MARKUP_ERROR
    enum                GMarkupParseFlags;
                        GMarkupParseContext;
                        GMarkupParser;
    gchar*              g_markup_escape_text                (const gchar *text,
                                                             gssize length);
    gchar*              g_markup_printf_escaped             (const char *format,
                                                             ...);
    gchar*              g_markup_vprintf_escaped            (const char *format,
                                                             va_list args);
    gboolean            g_markup_parse_context_end_parse    (GMarkupParseContext *context,
                                                             GError **error);
    void                g_markup_parse_context_free         (GMarkupParseContext *context);
    void                g_markup_parse_context_get_position (GMarkupParseContext *context,
                                                             gint *line_number,
                                                             gint *char_number);
    const gchar*        g_markup_parse_context_get_element  (GMarkupParseContext *context);
    GMarkupParseContext* g_markup_parse_context_new         (const GMarkupParser *parser,
                                                             GMarkupParseFlags flags,
                                                             gpointer user_data,
                                                             GDestroyNotify user_data_dnotify);
    gboolean            g_markup_parse_context_parse        (GMarkupParseContext *context,
                                                             const gchar *text,
                                                             gssize text_len,
                                                             GError **error);

## Description

The "GMarkup" parser is intended to parse a simple markup format that's a subset of XML. This is a small, efficient, easy-to-use parser. It should not be used if you expect to interoperate with other applications generating full-scale XML. However, it's very useful for application data files, config files, etc. where you know your application will be the only one writing the file. Full-scale XML parsers should be able to parse the subset used by GMarkup, so you can easily migrate to full-scale XML at a later time if the need arises.

GMarkup is not guaranteed to signal an error on all invalid XML; the parser may accept documents that an XML parser would not. However, XML documents which are not well-formed[4] are not considered valid GMarkup documents.

Simplifications to XML include:

- Only UTF-8 encoding is allowed.

- No user-defined entities.

- Processing instructions, comments and the doctype declaration are "passed through" but are not interpreted in any way.

- No DTD or validation.

The markup format does support:

- Elements

- Attributes

- 5 standard entities: `&amp; &lt; &gt; &quot; &apos;`

- Character references

- Sections marked as CDATA

## Details

### enum GMarkupError

    typedef enum
    {
      G_MARKUP_ERROR_BAD_UTF8,
      G_MARKUP_ERROR_EMPTY,
      G_MARKUP_ERROR_PARSE,
      /* These three are primarily intended for specific GMarkupParser
       * implementations to set.
       */
      G_MARKUP_ERROR_UNKNOWN_ELEMENT,
      G_MARKUP_ERROR_UNKNOWN_ATTRIBUTE,
      G_MARKUP_ERROR_INVALID_CONTENT
    } GMarkupError;

Error codes returned by markup parsing.

`G_MARKUP_ERROR_BAD_UTF8` | text being parsed was not valid UTF-8
`G_MARKUP_ERROR_EMPTY` | document contained nothing, or only whitespace
`G_MARKUP_ERROR_PARSE` | document was ill-formed
`G_MARKUP_ERROR_UNKNOWN_ELEMENT` | error should be set by GMarkupParser functions; element wasn't known
`G_MARKUP_ERROR_UNKNOWN_ATTRIBUTE` | error should be set by GMarkupParser functions; attribute wasn't known
`G_MARKUP_ERROR_INVALID_CONTENT` | error should be set by GMarkupParser functions; something was wrong with contents of the document, e.g. invalid attribute value

### G_MARKUP_ERROR

    #define G_MARKUP_ERROR g_markup_error_quark ()

Error domain for markup parsing. Errors in this domain will be from the GMarkupError enumeration. See GError for information on error domains.

### enum GMarkupParseFlags

    typedef enum
    {
      G_MARKUP_DO_NOT_USE_THIS_UNSUPPORTED_FLAG = 1 << 0,
      G_MARKUP_TREAT_CDATA_AS_TEXT              = 1 << 1
    } GMarkupParseFlags;

Flags that affect the behaviour of the parser.

`G_MARKUP_DO_NOT_USE_THIS_UNSUPPORTED_FLAG` | flag you should not use.
`G_MARKUP_TREAT_CDATA_AS_TEXT` | When this flag is set, CDATA marked sections are not passed literally to the `passthrough` function of the parser. Instead, the content of the section (without the `<![CDATA[` and `]]>`) is passed to the `text` function. This flag was added in GLib 2.12.

### GMarkupParseContext

    typedef struct _GMarkupParseContext GMarkupParseContext;

A parse context is used to parse a stream of bytes that you expect to contain marked-up text. See `g_markup_parse_context_new()`, GMarkupParser, and so on for more details.

### GMarkupParser

    typedef struct {
      /* Called for open tags <foo bar="baz"> */
      void (*start_element)  (GMarkupParseContext *context,
                              const gchar         *element_name,
                              const gchar        **attribute_names,
                              const gchar        **attribute_values,
                              gpointer             user_data,
                              GError             **error);

      /* Called for close tags </foo> */
      void (*end_element)    (GMarkupParseContext *context,
                              const gchar         *element_name,
                              gpointer             user_data,
                              GError             **error);

      /* Called for character data */
      /* text is not nul-terminated */
      void (*text)           (GMarkupParseContext *context,
                              const gchar         *text,
                              gsize                text_len,
                              gpointer             user_data,
                              GError             **error);

      /* Called for strings that should be re-saved verbatim in this same
       * position, but are not otherwise interpretable.  At the moment
       * this includes comments and processing instructions.
       */
      /* text is not nul-terminated. */
      void (*passthrough)    (GMarkupParseContext *context,
                              const gchar         *passthrough_text,
                              gsize                text_len,
                              gpointer             user_data,
                              GError             **error);

      /* Called on error, including one set by other
       * methods in the vtable. The GError should not be freed.
       */
      void (*error)          (GMarkupParseContext *context,
                              GError              *error,
                              gpointer             user_data);
    } GMarkupParser;

Any of the fields in GMarkupParser can be `NULL`, in which case they will be ignored. Except for the `error` function, any of these callbacks can set an error; in particular the `G_MARKUP_ERROR_UNKNOWN_ELEMENT`, `G_MARKUP_ERROR_UNKNOWN_ATTRIBUTE`, and `G_MARKUP_ERROR_INVALID_CONTENT` errors are intended to be set from these callbacks. If you set an error from a callback, `g_markup_parse_context_parse()` will report that error back to its caller.

`start_element` () | Callback to invoke when the opening tag of an element is seen.
`end_element` () | Callback to invoke when the closing tag of an element is seen. Note that this is also called for empty tags like `<empty/>`.
`text` () | Callback to invoke when some text is seen (text is always inside an element). Note that the text of an element may be spread over multiple calls of this function. If the `G_MARKUP_TREAT_CDATA_AS_TEXT` flag is set, this function is also called for the content of CDATA marked sections.
`passthrough` () | Callback to invoke for comments, processing instructions and doctype declarations; if you're re-writing the parsed document, write the passthrough text back out in the same position. If the `G_MARKUP_TREAT_CDATA_AS_TEXT` flag is not set, this function is also called for CDATA marked sections.
`error` () | Callback to invoke when an error occurs.

### g_markup_escape_text ()

    gchar*              g_markup_escape_text                (const gchar *text,
                                                             gssize length);

Escapes text so that the markup parser will parse it verbatim. Less than, greater than, ampersand, etc. are replaced with the corresponding entities. This function would typically be used when writing out a file to be parsed with the markup parser.

Note that this function doesn't protect whitespace and line endings from being processed according to the XML rules for normalization of line endings and attribute values.

`text` : | some valid UTF-8 text
`length` : | length of `text` in bytes, or -1 if the text is nul-terminated
Returns : | a newly allocated string with the escaped text

### g_markup_printf_escaped ()

    gchar*              g_markup_printf_escaped             (const char *format,
                                                             ...);

Formats arguments according to `format`, escaping all string and character arguments in the fashion of `g_markup_escape_text()`. This is useful when you want to insert literal strings into XML-style markup output, without having to worry that the strings might themselves contain markup.

    const char *store = "Fortnum & Mason";
    const char *item = "Tea";
    char *output;

    output = g_markup_printf_escaped ("<purchase>"
                                      "<store>%s</store>"
                                      "<item>%s</item>"
                                      "</purchase>",
                                      store, item);

`format` : | `printf()` style format string
`...` : | the arguments to insert in the format string
Returns : | newly allocated result from formatting operation. Free with `g_free()`.

Since 2.4

### g_markup_vprintf_escaped ()

    gchar*              g_markup_vprintf_escaped            (const char *format,
                                                             va_list args);

Formats the data in `args` according to `format`, escaping all string and character arguments in the fashion of `g_markup_escape_text()`. See `g_markup_printf_escaped()`.

`format` : | `printf()` style format string
`args` : | variable argument list, similar to `vprintf()`
Returns : | newly allocated result from formatting operation. Free with `g_free()`.

Since 2.4

### g_markup_parse_context_end_parse ()

    gboolean            g_markup_parse_context_end_parse    (GMarkupParseContext *context,
                                                             GError **error);

Signals to the GMarkupParseContext that all data has been fed into the parse context with `g_markup_parse_context_parse()`. This function reports an error if the document isn't complete, for example if elements are still open.

`context` : | a GMarkupParseContext
`error` : | return location for a GError
Returns : | `TRUE` on success, `FALSE` if an error was set

### g_markup_parse_context_free ()

    void                g_markup_parse_context_free         (GMarkupParseContext *context);

Frees a GMarkupParseContext. Can't be called from inside one of the GMarkupParser functions.

`context` : | a GMarkupParseContext

### g_markup_parse_context_get_position ()

    void                g_markup_parse_context_get_position (GMarkupParseContext *context,
                                                             gint *line_number,
                                                             gint *char_number);

Retrieves the current line number and the number of the character on that line. Intended for use in error messages; there are no strict semantics for what constitutes the "current" line number other than "the best number we could come up with for error messages."

`context` : | a GMarkupParseContext
`line_number` : | return location for a line number, or `NULL`
`char_number` : | return location for a char-on-line number, or `NULL`

### g_markup_parse_context_get_element ()

    const gchar*        g_markup_parse_context_get_element  (GMarkupParseContext *context);

Retrieves the name of the currently open element.

`context` : | a GMarkupParseContext
Returns : | the name of the currently open element, or `NULL`

Since 2.2

### g_markup_parse_context_new ()

    GMarkupParseContext* g_markup_parse_context_new         (const GMarkupParser *parser,
                                                             GMarkupParseFlags flags,
                                                             gpointer user_data,
                                                             GDestroyNotify user_data_dnotify);

Creates a new parse context. A parse context is used to parse marked-up documents. You can feed any number of documents into a context, as long as no errors occur; once an error occurs, the parse context can't continue to parse text (you have to free it and create a new parse context).

`parser` : | a GMarkupParser
`flags` : | one or more GMarkupParseFlags
`user_data` : | user data to pass to GMarkupParser functions
`user_data_dnotify` : | user data destroy notifier called when the parse context is freed
Returns : | a new GMarkupParseContext

### g_markup_parse_context_parse ()

    gboolean            g_markup_parse_context_parse        (GMarkupParseContext *context,
                                                             const gchar *text,
                                                             gssize text_len,
                                                             GError **error);

Feed some data to the GMarkupParseContext. The data need not be valid UTF-8; an error will be signaled if it's invalid. The data need not be an entire document; you can feed a document into the parser incrementally, via multiple calls to this function. Typically, as you receive data from a network connection or file, you feed each received chunk of data into this function, aborting the process if an error occurs. Once an error is reported, no further data may be fed to the GMarkupParseContext; all errors are fatal.

`context` : | a GMarkupParseContext
`text` : | chunk of text to parse
`text_len` : | length of `text` in bytes
`error` : | return location for a GError
Returns : | `FALSE` if an error occurred, `TRUE` on success

[4] XML specification