VistaIOGetAttrValue(3) fetch an attribute's value

Other Alias



VistaIOGetAttrResult VistaIOGetAttr (list, name, dict, repn, value)

VistaIOAttrList list; VistaIOStringConst name; VistaIODictEntry *dict; VistaIORepnKind repn; VistaIOPointer value;
typedef enum { VistaIOAttrFound, VistaIOAttrMissing, VistaIOAttrBadValue } VistaIOGetAttrResult; VistaIOBoolean VistaIOGetAttrValue (posn, dict, repn, value)
VistaIOAttrListPosn *posn; VistaIODictEntry *dict; VistaIORepnKind repn; VistaIOPointer value;


Specifies the list of attributes to be searched by name for the desired attribute.
Specifies the name of the desired attribute.
Specifies the position of the desired attribute within its attribute list.
May specify a dictionary to be used in recognizing a keyword stored as the attribute's value, or it may be NULL
Specifies the representation in which the attribute value is to be returned.
Specifies a location at which the attribute value is be returned.


These routines both return an attribute's value, but they differ in how the attribute is identified:
  • VistaIOGetAttr fetches the value of the first attribute with the name name in the list list.
  • VistaIOGetAttrValue fetches the value of the attribute whose position within an attribute list is posn.

If a dictionary, dict, has been provided and the attribute's value is stored as a character string, the routine determines whether the string is a keyword defined in the dictionary. If so, it uses the value associated with that keyword rather than the attribute's original value. (See the VistaIOdictionary(3) manual page.)

The value obtained directly from the attribute, or indirectly via the dictionary, is converted to the representation repn and then stored at the location pointed to by value. The repn argument may have any VistaIORepnKind value (any of the values returned by VistaIORegisterType(3). However, an attribute value that is a string can only be returned as a string or a number, and other attribute values can only be returned in the representation with which they are stored. (The VistaIOGetAttrRepn(3) macro can be used to determine an attribute value's representation.)

If repn calls for a number to be returned, the caller receives a copy of the value stored with the attribute. If, on the other hand, it calls for a string, attribute list, pointer, image, edge set, etc. to be returned, the caller receives a pointer to the same value as that stored with the attribute.


If the specified attribute is not found, VistaIOGetAttr returns VistaIOAttrMissing. If it is found but its value cannot be converted to the desired representation, VistaIOGetAttr returns VistaIOAttrBadValue. Otherwise, VistaIOGetAttr is successful and it returns VistaIOAttrFound, having stored the attribute's value at *value.

VistaIOGetAttrValue returns TRUE if it is successfully returning the attribute's value at *value, and FALSE if the value cannot be converted to the desired representation.


The following code fragment prints the name of an image:

VistaIOImage image;
VistaIOStringConst name;
if (VistaIOGetAttr (VistaIOImageAttrList (image), VistaIONameAttr, NULL, 
VistaIOStringRepn, (VistaIOPointer) & name) == VistaIOAttrFound) printf ("Name: %s\n", name);


VistaIOGetAttr is meant for use with attribute lists representing sets, in which each attribute name occurs at most once. If list contains multiple attributes named name, only the first is located and returned.

The value argument must point to sufficient storage to contain a value of the representation requested. Neither the routine nor the C compiler can automatically check that this is so.


Art Pope <[email protected]>

Adaption to vistaio: Gert Wollny <[email protected]>