The AST library makes extensive use of pointers, not only for accessing Objects directly, but also as a means of storing Objects inside other Objects (a number of classes of Object are designed to hold collections of other Objects). Rather than copy an Object in its entirety, a pointer to the interior Object is simply stored in the enclosing Object.
This means that Objects may frequently not be completely independent of each other because, for instance, they both contain pointers to the same sub-Object. In this situation, changing one Object (say assigning an attribute value) may affect the other one via the common Object.
It is difficult to describe all cases where this may happen, so you should always be alert to the possibility. Fortunately, there is a simple solution. If you require two Objects to be independent, then simply use astCopy to make a copy of one, e.g:
AstZoomMap *zoommap1, *zoommap2; ... zoommap2 = astCopy( zoommap1 );
This process will create a true copy of any Object and return a pointer to the copy. This copy will not contain any pointers to any component of the original Object (everything is duplicated), so you can then modify it safely, without fear of affecting either the original or any other Object.
AST A Library for Handling World Coordinate Systems in Astronomy