Validating Input

The pointer returned by astReadastRead (15.4) could identify any class of ObjectObject--this is determined entirely by the external data being read. If it is necessary to test for a particular class (say a FrameFrame), this may be done as follows using the appropriate member of the astIsA$<$Class$>$astIsAClass family of functions:

int ok;

...

ok = astIsAFrame( object );

Note, however, that this will accept any Frame, so would be equally happy with a basic Frame or a SkyFrameSkyFrame. An alternative validation strategy would be to obtain the value of the Object's ClassClass attribute and then test this character string, as follows:

#include <string.h>

...

ok = !strcmp( astGetC( object, "Class" ), "Frame" );

This would only accept a basic Frame and would reject a SkyFrame.