Organization of Extended Data

AutoLISP Developer's Guide > Using the AutoLISP Language > Using AutoLISP to Manipulate AutoCAD Objects > Extended Data - xdata >

Extended data consists of one or more 1001 groups, each of which begins with a unique application name. The xdata groups returned by entget follow the definition data in the order in which they are saved in the database.

Within each application's group, the contents, meaning, and organization of the data are defined by the application. AutoCAD maintains the information but does not use it. The table also shows that the group codes for xdata are in the range 1000-1071. Many of these group codes are for familiar data types, as follows:

String: 1000. Strings in extended data can be up to 255 bytes long (with the 256th byte reserved for the null character).
Application Name: 1001 (also a string value). Application names can be up to 31 bytes long (the 32nd byte is reserved for the null character) and must adhere to the rules for symbol table names (such as layer names). An application name can contain letters, digits, and the special characters $ (dollar sign), - (hyphen), and _ (underscore). It cannot contain spaces.
Layer Name: 1003. Name of a layer associated with the xdata.
Database -Handle: 1005. Handle of an entity in the drawing database.
3D Point: 1010. Three real values, contained in a point.
Real: 1040. A real value.
Integer: 1070. A 16-bit integer (signed or unsigned).
Long: 1071. A 32-bit signed (long) integer. If the value that appears in a 1071 group is a short integer or real value, it is converted to a long integer; if it is invalid (for example, a string), it is converted to a long zero (0L).

NoteAutoLISP manages 1071 groups as real values. If you use entget to retrieve an entity's definition list that contains a 1071 group, the value is returned as a real, as shown in the following example:

(1071 . 12.0)

If you want to create a 1071 group in an entity with entmake or entmod, you can use either a real or an integer value, as shown in the following example:

(entmake '((..... (1071 . 12) .... )))

(entmake '((..... (1071 . 12.0) .... )))

(entmake '((..... (1071 . 65537.0) .... )))

(entmake '((..... (1071 . 65537) .... )))

But AutoLISP still returns the group value as a real:

(entmake '((..... (1071 . 65537) .... )))

The preceding statement returns the following:

(1071 . 65537.0)

ObjectARX always manages 1071 groups as long integers.

Several other extended data groups have special meanings in this context (if the application chooses to use them):

Control String: 1002. An xdata control string can be either "{" or "}". These braces enable the application to organize its data by subdividing it into lists. The left brace begins a list, and the right brace terminates the most recent list. Lists can be nested.

NoteIf a 1001 group appears within a list, it is treated as a string and does not begin a new application group.
Binary Data: 1004. Binary data that is organized into variable-length chunks, which can be handled in ObjectARX with the ads_binary structure. The maximum length of each chunk is 127 bytes.

NoteAutoLISP cannot directly handle binary chunks, so the same precautions that apply to long (1071) groups apply to binary groups as well.
World Space Position: 1011. Unlike a simple 3D point, the WCS coordinates are moved, scaled, rotated, and mirrored along with the parent entity to which the extended data belongs. The WCS position is also stretched when the STRETCH command is applied to the parent entity and when this point lies within the select window.
World Space -Displacement: 1012. A 3D point that is scaled, rotated, or mirrored along with the parent, but not stretched or moved.
World -Direction: 1013. A 3D point that is rotated or mirrored along with the parent, but not scaled, stretched, or moved. The WCS direction is a normalized displacement that always has a unit length.
Distance: 1041. A real value that is scaled along with the parent entity.
Scale Factor: 1042. Also a real value that is scaled along with the parent.

The DXF group codes for xdata are also described in the DXF Reference.