This function is intended primarily as a means of iterating round all the elements in a KeyMap. For this purpose, the number of entries in the KeyMap should first be found using astMapSize and this function should then be called in a loop, with the index value going from zero to one less than the size of the KeyMap. The index associated with a given entry is determined by the SortBy attribute.
"is the value returned by the astMapSize function.
The returned pointer is guaranteed to remain valid and the string to which it points will not be over-written for a total of 50 successive invocations of this function. After this, the memory containing the string may be re-used, so a copy of the string should be made if it is needed for longer than this.
A NULL pointer will be returned if this function is invoked with the AST error status set, or if it should fail for any reason.