Such warnings are non-fatal and will not prevent the read or write operation succeeding. However, the converted object may not be identical to the original object in all respects. Differences which would usually be deemed as insignificant in most usual cases will generate a warning, whereas more significant differences will generate an error.
" attribute allows this warning facility to be switched off, so that a fatal error is always
reported for any conversion error.
As AST continues to be developed, new attributes are added occasionally to selected classes. If an older version of AST is used to read external Object descriptions created by a more recent version of AST, then the Channel class will, by default, ignore the new attributes, using the remaining attributes to construct the Object. This is usually a good thing. However, since external Object descriptions are often stored in plain text, it is possible to edit them using a text editor. This gives rise to the possibility of genuine errors in the description due to finger-slips, typos, or simple mis-understanding. Such inappropriate attributes will be ignored if Strict is left at its default zero value. This will cause the mis-spelled attribute to revert to its default value, potentially causing subtle changes in the behaviour of application software. If such an effect is suspected, the Strict attribute can be set non-zero, resulting in the erroneous attribute being identified in an error message.
The returned KeyMap uses keys of the form
" , etc.
A value of AST__NULL will be returned if this function is invoked with STATUS set to an error value, or if it should fail for any reason.