Management of Extended Data Memory Use

Extended data is currently limited to 16K per entity. Because the xdata of an entity can be created and maintained by multiple applications, problems can result when the size of the xdata approaches its limit. AutoLISP provides two functions, xdsize and xdroom, to assist in managing the memory that xdata occupies. When xdsize is passed a list of xdata, it returns the amount of memory (in bytes) that the data will occupy. When xdroom is passed the name of an entity, it returns the remaining number of free bytes that can still be appended to the entity.

The xdsize function reads an extended data list, which can be large. This function can be slow, so it is not recommended that you call it frequently. A better approach is to use it (in conjunction with xdroom) in an error handler. If a call to entmod fails, you can use xdsize and xdroom to find out whether the call failed because the entity didn't have enough room for the xdata.