GstStructure

GstStructure — Generic structure containing fields of names and values

Synopsis


#include <gst/gst.h>


                    GstStructure;
gboolean            (*GstStructureForeachFunc)          (GQuark field_id,
                                                         const GValue *value,
                                                         gpointer user_data);
gboolean            (*GstStructureMapFunc)              (GQuark field_id,
                                                         GValue *value,
                                                         gpointer user_data);
GstStructure*       gst_structure_empty_new             (const gchar *name);
GstStructure*       gst_structure_id_empty_new          (GQuark quark);
GstStructure*       gst_structure_new                   (const gchar *name,
                                                         const gchar *firstfield,
                                                         ...);
GstStructure*       gst_structure_new_valist            (const gchar *name,
                                                         const gchar *firstfield,
                                                         va_list varargs);
GstStructure*       gst_structure_copy                  (const GstStructure *structure);
void                gst_structure_free                  (GstStructure *structure);
const gchar*        gst_structure_get_name              (const GstStructure *structure);
gboolean            gst_structure_has_name              (const GstStructure *structure,
                                                         const gchar *name);
void                gst_structure_set_name              (GstStructure *structure,
                                                         const gchar *name);
GQuark              gst_structure_get_name_id           (const GstStructure *structure);
const GValue*       gst_structure_id_get_value          (const GstStructure *structure,
                                                         GQuark field);
void                gst_structure_id_set_value          (GstStructure *structure,
                                                         GQuark field,
                                                         const GValue *value);
const GValue*       gst_structure_get_value             (const GstStructure *structure,
                                                         const gchar *fieldname);
void                gst_structure_set_value             (GstStructure *structure,
                                                         const gchar *fieldname,
                                                         const GValue *value);
void                gst_structure_set                   (GstStructure *structure,
                                                         const gchar *fieldname,
                                                         ...);
void                gst_structure_set_valist            (GstStructure *structure,
                                                         const gchar *fieldname,
                                                         va_list varargs);
void                gst_structure_id_set                (GstStructure *structure,
                                                         GQuark fieldname,
                                                         ...);
void                gst_structure_id_set_valist         (GstStructure *structure,
                                                         GQuark fieldname,
                                                         va_list varargs);
void                gst_structure_remove_field          (GstStructure *structure,
                                                         const gchar *fieldname);
void                gst_structure_remove_fields         (GstStructure *structure,
                                                         const gchar *fieldname,
                                                         ...);
void                gst_structure_remove_fields_valist  (GstStructure *structure,
                                                         const gchar *fieldname,
                                                         va_list varargs);
void                gst_structure_remove_all_fields     (GstStructure *structure);
GType               gst_structure_get_field_type        (const GstStructure *structure,
                                                         const gchar *fieldname);
gboolean            gst_structure_foreach               (const GstStructure *structure,
                                                         GstStructureForeachFunc func,
                                                         gpointer user_data);
gint                gst_structure_n_fields              (const GstStructure *structure);
gboolean            gst_structure_has_field             (const GstStructure *structure,
                                                         const gchar *fieldname);
gboolean            gst_structure_has_field_typed       (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         GType type);
gboolean            gst_structure_get_boolean           (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         gboolean *value);
gboolean            gst_structure_get_int               (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         gint *value);
gboolean            gst_structure_get_fourcc            (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         guint32 *value);
gboolean            gst_structure_get_double            (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         gdouble *value);
const gchar*        gst_structure_get_string            (const GstStructure *structure,
                                                         const gchar *fieldname);
gboolean            gst_structure_get_date              (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         GDate **value);
gboolean            gst_structure_get_clock_time        (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         GstClockTime *value);
gboolean            gst_structure_get_enum              (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         GType enumtype,
                                                         gint *value);
gboolean            gst_structure_get_fraction          (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         gint *value_numerator,
                                                         gint *value_denominator);
gboolean            gst_structure_map_in_place          (GstStructure *structure,
                                                         GstStructureMapFunc func,
                                                         gpointer user_data);
const gchar*        gst_structure_nth_field_name        (const GstStructure *structure,
                                                         guint index);
void                gst_structure_set_parent_refcount   (GstStructure *structure,
                                                         gint *refcount);
gchar*              gst_structure_to_string             (const GstStructure *structure);
GstStructure*       gst_structure_from_string           (const gchar *string,
                                                         gchar **end);
gboolean            gst_structure_fixate_field_nearest_int
                                                        (GstStructure *structure,
                                                         const char *field_name,
                                                         int target);
gboolean            gst_structure_fixate_field_nearest_double
                                                        (GstStructure *structure,
                                                         const char *field_name,
                                                         double target);
gboolean            gst_structure_fixate_field_nearest_fraction
                                                        (GstStructure *structure,
                                                         const char *field_name,
                                                         const gint target_numerator,
                                                         const gint target_denominator);
gboolean            gst_structure_fixate_field_boolean  (GstStructure *structure,
                                                         const char *field_name,
                                                         gboolean target);


Description

A GstStructure is a collection of key/value pairs. The keys are expressed as GQuarks and the values can be of any GType.

In addition to the key/value pairs, a GstStructure also has a name.

GstStructure is used by various GStreamer subsystems to store information in a flexible and extensible way. A GstStructure does not have a refcount because it usually is part of a higher level object such as GstCaps. It provides a means to enforce mutability using the refcount of the parent with the gst_structure_set_parent_refcount() method.

A GstStructure can be created with gst_structure_empty_new() or gst_structure_new(), which both take a name and an optional set of key/value pairs along with the types of the values.

Field values can be changed with gst_structure_set_value() or gst_structure_set().

Field values can be retrieved with gst_structure_get_value() or the more convenient gst_structure_get_*() functions.

Fields can be removed with gst_structure_remove_field() or gst_structure_remove_fields().

Last reviewed on 2005-11-09 (0.9.4)

Details

GstStructure

typedef struct {
  GType type;
} GstStructure;

The GstStructure object. Most fields are private.

GType type; the GType of a structure

GstStructureForeachFunc ()

gboolean            (*GstStructureForeachFunc)          (GQuark field_id,
                                                         const GValue *value,
                                                         gpointer user_data);

A function that will be called in gst_structure_foreach(). The function may not modify value.

field_id : the GQuark of the field name
value : the GValue of the field
user_data : user data
Returns : TRUE if the foreach operation should continue, FALSE if the foreach operation should stop with FALSE.

GstStructureMapFunc ()

gboolean            (*GstStructureMapFunc)              (GQuark field_id,
                                                         GValue *value,
                                                         gpointer user_data);

A function that will be called in gst_structure_map_in_place(). The function may modify value.

field_id : the GQuark of the field name
value : the GValue of the field
user_data : user data
Returns : TRUE if the map operation should continue, FALSE if the map operation should stop with FALSE.

gst_structure_empty_new ()

GstStructure*       gst_structure_empty_new             (const gchar *name);

Creates a new, empty GstStructure with the given name.

name : name of new structure
Returns : a new, empty GstStructure

gst_structure_id_empty_new ()

GstStructure*       gst_structure_id_empty_new          (GQuark quark);

Creates a new, empty GstStructure with the given name as a GQuark.

quark : name of new structure
Returns : a new, empty GstStructure

gst_structure_new ()

GstStructure*       gst_structure_new                   (const gchar *name,
                                                         const gchar *firstfield,
                                                         ...);

Creates a new GstStructure with the given name. Parses the list of variable arguments and sets fields to the values listed. Variable arguments should be passed as field name, field type, and value. Last variable argument should be NULL.

name : name of new structure
firstfield : name of first field to set
... : additional arguments
Returns : a new GstStructure

gst_structure_new_valist ()

GstStructure*       gst_structure_new_valist            (const gchar *name,
                                                         const gchar *firstfield,
                                                         va_list varargs);

Creates a new GstStructure with the given name. Structure fields are set according to the varargs in a manner similar to gst_structure_new.

name : name of new structure
firstfield : name of first field to set
varargs : variable argument list
Returns : a new GstStructure

gst_structure_copy ()

GstStructure*       gst_structure_copy                  (const GstStructure *structure);

Duplicates a GstStructure and all its fields and values.

structure : a GstStructure to duplicate
Returns : a new GstStructure.

gst_structure_free ()

void                gst_structure_free                  (GstStructure *structure);

Frees a GstStructure and all its fields and values. The structure must not have a parent when this function is called.

structure : the GstStructure to free

gst_structure_get_name ()

const gchar*        gst_structure_get_name              (const GstStructure *structure);

Get the name of structure as a string.

structure : a GstStructure
Returns : the name of the structure.

gst_structure_has_name ()

gboolean            gst_structure_has_name              (const GstStructure *structure,
                                                         const gchar *name);

Checks if the structure has the given name

structure : a GstStructure
name : structure name to check for
Returns : TRUE if name matches the name of the structure.

gst_structure_set_name ()

void                gst_structure_set_name              (GstStructure *structure,
                                                         const gchar *name);

Sets the name of the structure to the given name. The string provided is copied before being used.

structure : a GstStructure
name : the new name of the structure

gst_structure_get_name_id ()

GQuark              gst_structure_get_name_id           (const GstStructure *structure);

Get the name of structure as a GQuark.

structure : a GstStructure
Returns : the quark representing the name of the structure.

gst_structure_id_get_value ()

const GValue*       gst_structure_id_get_value          (const GstStructure *structure,
                                                         GQuark field);

Get the value of the field with GQuark field.

structure : a GstStructure
field : the GQuark of the field to get
Returns : the GValue corresponding to the field with the given name identifier.

gst_structure_id_set_value ()

void                gst_structure_id_set_value          (GstStructure *structure,
                                                         GQuark field,
                                                         const GValue *value);

Sets the field with the given GQuark field to value. If the field does not exist, it is created. If the field exists, the previous value is replaced and freed.

structure : a GstStructure
field : a GQuark representing a field
value : the new value of the field

gst_structure_get_value ()

const GValue*       gst_structure_get_value             (const GstStructure *structure,
                                                         const gchar *fieldname);

Get the value of the field with name fieldname.

structure : a GstStructure
fieldname : the name of the field to get
Returns : the GValue corresponding to the field with the given name.

gst_structure_set_value ()

void                gst_structure_set_value             (GstStructure *structure,
                                                         const gchar *fieldname,
                                                         const GValue *value);

Sets the field with the given name field to value. If the field does not exist, it is created. If the field exists, the previous value is replaced and freed.

structure : a GstStructure
fieldname : the name of the field to set
value : the new value of the field

gst_structure_set ()

void                gst_structure_set                   (GstStructure *structure,
                                                         const gchar *fieldname,
                                                         ...);

Parses the variable arguments and sets fields accordingly. Variable arguments should be in the form field name, field type (as a GType), value(s). The last variable argument should be NULL.

structure : a GstStructure
fieldname : the name of the field to set
... : variable arguments

gst_structure_set_valist ()

void                gst_structure_set_valist            (GstStructure *structure,
                                                         const gchar *fieldname,
                                                         va_list varargs);

va_list form of gst_structure_set().

structure : a GstStructure
fieldname : the name of the field to set
varargs : variable arguments

gst_structure_id_set ()

void                gst_structure_id_set                (GstStructure *structure,
                                                         GQuark fieldname,
                                                         ...);

Identical to gst_structure_set, except that field names are passed using the GQuark for the field name. This allows more efficient setting of the structure if the caller already knows the associated quark values. The last variable argument must be NULL.

structure : a GstStructure
fieldname : the GQuark for the name of the field to set
... : variable arguments

Since 0.10.10


gst_structure_id_set_valist ()

void                gst_structure_id_set_valist         (GstStructure *structure,
                                                         GQuark fieldname,
                                                         va_list varargs);

va_list form of gst_structure_id_set().

structure : a GstStructure
fieldname : the name of the field to set
varargs : variable arguments

Since 0.10.10


gst_structure_remove_field ()

void                gst_structure_remove_field          (GstStructure *structure,
                                                         const gchar *fieldname);

Removes the field with the given name. If the field with the given name does not exist, the structure is unchanged.

structure : a GstStructure
fieldname : the name of the field to remove

gst_structure_remove_fields ()

void                gst_structure_remove_fields         (GstStructure *structure,
                                                         const gchar *fieldname,
                                                         ...);

Removes the fields with the given names. If a field does not exist, the argument is ignored.

structure : a GstStructure
fieldname : the name of the field to remove
... : NULL-terminated list of more fieldnames to remove

gst_structure_remove_fields_valist ()

void                gst_structure_remove_fields_valist  (GstStructure *structure,
                                                         const gchar *fieldname,
                                                         va_list varargs);

va_list form of gst_structure_remove_fields().

structure : a GstStructure
fieldname : the name of the field to remove
varargs : NULL-terminated list of more fieldnames to remove

gst_structure_remove_all_fields ()

void                gst_structure_remove_all_fields     (GstStructure *structure);

Removes all fields in a GstStructure.

structure : a GstStructure

gst_structure_get_field_type ()

GType               gst_structure_get_field_type        (const GstStructure *structure,
                                                         const gchar *fieldname);

Finds the field with the given name, and returns the type of the value it contains. If the field is not found, G_TYPE_INVALID is returned.

structure : a GstStructure
fieldname : the name of the field
Returns : the GValue of the field

gst_structure_foreach ()

gboolean            gst_structure_foreach               (const GstStructure *structure,
                                                         GstStructureForeachFunc func,
                                                         gpointer user_data);

Calls the provided function once for each field in the GstStructure. The function must not modify the fields. Also see gst_structure_map_in_place().

structure : a GstStructure
func : a function to call for each field
user_data : private data
Returns : TRUE if the supplied function returns TRUE For each of the fields, FALSE otherwise.

gst_structure_n_fields ()

gint                gst_structure_n_fields              (const GstStructure *structure);

Get the number of fields in the structure.

structure : a GstStructure
Returns : the number of fields in the structure

gst_structure_has_field ()

gboolean            gst_structure_has_field             (const GstStructure *structure,
                                                         const gchar *fieldname);

Check if structure contains a field named fieldname.

structure : a GstStructure
fieldname : the name of a field
Returns : TRUE if the structure contains a field with the given name

gst_structure_has_field_typed ()

gboolean            gst_structure_has_field_typed       (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         GType type);

Check if structure contains a field named fieldname and with GType type.

structure : a GstStructure
fieldname : the name of a field
type : the type of a value
Returns : TRUE if the structure contains a field with the given name and type

gst_structure_get_boolean ()

gboolean            gst_structure_get_boolean           (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         gboolean *value);

Sets the boolean pointed to by value corresponding to the value of the given field. Caller is responsible for making sure the field exists and has the correct type.

structure : a GstStructure
fieldname : the name of a field
value : a pointer to a gboolean to set
Returns : TRUE if the value could be set correctly. If there was no field with fieldname or the existing field did not contain a boolean, this function returns FALSE.

gst_structure_get_int ()

gboolean            gst_structure_get_int               (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         gint *value);

Sets the int pointed to by value corresponding to the value of the given field. Caller is responsible for making sure the field exists and has the correct type.

Returns: TRUE if the value could be set correctly. If there was no field with fieldname or the existing field did not contain an int, this function

structure : a GstStructure
fieldname : the name of a field
value : a pointer to an int to set
Returns : FALSE.

gst_structure_get_fourcc ()

gboolean            gst_structure_get_fourcc            (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         guint32 *value);

Sets the GstFourcc pointed to by value corresponding to the value of the given field. Caller is responsible for making sure the field exists and has the correct type.

Returns: TRUE if the value could be set correctly. If there was no field with fieldname or the existing field did not contain a fourcc, this function

structure : a GstStructure
fieldname : the name of a field
value : a pointer to a GstFourcc to set
Returns : FALSE.

gst_structure_get_double ()

gboolean            gst_structure_get_double            (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         gdouble *value);

Sets the double pointed to by value corresponding to the value of the given field. Caller is responsible for making sure the field exists and has the correct type.

structure : a GstStructure
fieldname : the name of a field
value : a pointer to a GstFourcc to set
Returns : TRUE if the value could be set correctly. If there was no field with fieldname or the existing field did not contain a double, this function returns FALSE.

gst_structure_get_string ()

const gchar*        gst_structure_get_string            (const GstStructure *structure,
                                                         const gchar *fieldname);

Finds the field corresponding to fieldname, and returns the string contained in the field's value. Caller is responsible for making sure the field exists and has the correct type.

The string should not be modified, and remains valid until the next call to a gst_structure_*() function with the given structure.

structure : a GstStructure
fieldname : the name of a field
Returns : a pointer to the string or NULL when the field did not exist or did not contain a string.

gst_structure_get_date ()

gboolean            gst_structure_get_date              (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         GDate **value);

Sets the date pointed to by value corresponding to the date of the given field. Caller is responsible for making sure the field exists and has the correct type.

Returns: TRUE if the value could be set correctly. If there was no field with fieldname or the existing field did not contain a data, this function

structure : a GstStructure
fieldname : the name of a field
value : a pointer to a GDate to set
Returns : FALSE.

gst_structure_get_clock_time ()

gboolean            gst_structure_get_clock_time        (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         GstClockTime *value);

Sets the clock time pointed to by value corresponding to the clock time of the given field. Caller is responsible for making sure the field exists and has the correct type.

structure : a GstStructure
fieldname : the name of a field
value : a pointer to a GstClockTime to set
Returns : TRUE if the value could be set correctly. If there was no field with fieldname or the existing field did not contain a GstClockTime, this function returns FALSE.

gst_structure_get_enum ()

gboolean            gst_structure_get_enum              (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         GType enumtype,
                                                         gint *value);

Sets the int pointed to by value corresponding to the value of the given field. Caller is responsible for making sure the field exists, has the correct type and that the enumtype is correct.

structure : a GstStructure
fieldname : the name of a field
enumtype : the enum type of a field
value : a pointer to an int to set
Returns : TRUE if the value could be set correctly. If there was no field with fieldname or the existing field did not contain an enum of the given type, this function returns FALSE.

gst_structure_get_fraction ()

gboolean            gst_structure_get_fraction          (const GstStructure *structure,
                                                         const gchar *fieldname,
                                                         gint *value_numerator,
                                                         gint *value_denominator);

Sets the integers pointed to by value_numerator and value_denominator corresponding to the value of the given field. Caller is responsible for making sure the field exists and has the correct type.

structure : a GstStructure
fieldname : the name of a field
value_numerator : a pointer to an int to set
value_denominator : a pointer to an int to set
Returns : TRUE if the values could be set correctly. If there was no field with fieldname or the existing field did not contain a GstFraction, this function returns FALSE.

gst_structure_map_in_place ()

gboolean            gst_structure_map_in_place          (GstStructure *structure,
                                                         GstStructureMapFunc func,
                                                         gpointer user_data);

Calls the provided function once for each field in the GstStructure. In contrast to gst_structure_foreach(), the function may modify but not delete the fields. The structure must be mutable.

structure : a GstStructure
func : a function to call for each field
user_data : private data
Returns : TRUE if the supplied function returns TRUE For each of the fields, FALSE otherwise.

gst_structure_nth_field_name ()

const gchar*        gst_structure_nth_field_name        (const GstStructure *structure,
                                                         guint index);

Get the name of the given field number, counting from 0 onwards.

structure : a GstStructure
index : the index to get the name of
Returns : the name of the given field number

gst_structure_set_parent_refcount ()

void                gst_structure_set_parent_refcount   (GstStructure *structure,
                                                         gint *refcount);

Sets the parent_refcount field of GstStructure. This field is used to determine whether a structure is mutable or not. This function should only be called by code implementing parent objects of GstStructure, as described in the MT Refcounting section of the design documents.

structure : a GstStructure
refcount : a pointer to the parent's refcount

gst_structure_to_string ()

gchar*              gst_structure_to_string             (const GstStructure *structure);

Converts structure to a human-readable string representation.

structure : a GstStructure
Returns : a pointer to string allocated by g_malloc(). g_free() after usage.

gst_structure_from_string ()

GstStructure*       gst_structure_from_string           (const gchar *string,
                                                         gchar **end);

Creates a GstStructure from a string representation. If end is not NULL, a pointer to the place inside the given string where parsing ended will be returned.

string : a string representation of a GstStructure.
end : pointer to store the end of the string in.
Returns : a new GstStructure or NULL when the string could not be parsed. Free after usage.

gst_structure_fixate_field_nearest_int ()

gboolean            gst_structure_fixate_field_nearest_int
                                                        (GstStructure *structure,
                                                         const char *field_name,
                                                         int target);

Fixates a GstStructure by changing the given field to the nearest integer to target that is a subset of the existing field.

structure : a GstStructure
field_name : a field in structure
target : the target value of the fixation
Returns : TRUE if the structure could be fixated

gst_structure_fixate_field_nearest_double ()

gboolean            gst_structure_fixate_field_nearest_double
                                                        (GstStructure *structure,
                                                         const char *field_name,
                                                         double target);

Fixates a GstStructure by changing the given field to the nearest double to target that is a subset of the existing field.

structure : a GstStructure
field_name : a field in structure
target : the target value of the fixation
Returns : TRUE if the structure could be fixated

gst_structure_fixate_field_nearest_fraction ()

gboolean            gst_structure_fixate_field_nearest_fraction
                                                        (GstStructure *structure,
                                                         const char *field_name,
                                                         const gint target_numerator,
                                                         const gint target_denominator);

Fixates a GstStructure by changing the given field to the nearest fraction to target_numerator/target_denominator that is a subset of the existing field.

structure : a GstStructure
field_name : a field in structure
target_numerator : The numerator of the target value of the fixation
target_denominator : The denominator of the target value of the fixation
Returns : TRUE if the structure could be fixated

gst_structure_fixate_field_boolean ()

gboolean            gst_structure_fixate_field_boolean  (GstStructure *structure,
                                                         const char *field_name,
                                                         gboolean target);

Fixates a GstStructure by changing the given field_name field to the given target boolean if that field is not fixed yet.

structure : a GstStructure
field_name : a field in structure
target : the target value of the fixation
Returns : TRUE if the structure could be fixated

See Also

GstCaps, GstMessage, GstEvent, GstQuery