Format a coordinate value for a Frame axis astFormat
’
s attributes and, in particular, by any Format attribute string
that has been set for the axis. A suitable default format (based on the
Digits attribute value) will be applied if necessary. 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 formatted value may be converted back into a numerical (double) value using astUnformat.
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.