Question on run time error codes

[Jerry DeLisle <jvdelisle at verizon dot net>]

I have been adding some runtime error checks to the arrayio routines and I have 
a question.

How do I make an error code accessible at run time as meaningful.  For example 
if I use IOSTAT=ierr in a write statement, I can test for ierr=13, which is 
processor dependent.  But if we add an error code, that number may change and 
impact previous files.

Are the error names ERROR_WHATEVER accessible at run time by some method?

Is it policy to always add new codes to the end of the list so that all previous 
codes are not changed? see example from libgfortran.f where I am adding the 
array stride error:

typedef enum
{
  ERROR_FIRST = -3,		/* Marker for the first error.  */
  ERROR_EOR = -2,
  ERROR_END = -1,
  ERROR_OK = 0,			/* Indicates success, must be zero.  */
  ERROR_OS,			/* Operating system error, more info in errno.  */
  ERROR_OPTION_CONFLICT,
  ERROR_BAD_OPTION,
  ERROR_MISSING_OPTION,
  ERROR_ALREADY_OPEN,
  ERROR_BAD_UNIT,
  ERROR_FORMAT,
  ERROR_BAD_ACTION,
  ERROR_ENDFILE,
  ERROR_BAD_US,
  ERROR_READ_VALUE,
  ERROR_READ_OVERFLOW,
  ERROR_ARRAY_STRIDE,
  ERROR_LAST			/* Not a real error, the last error # + 1.  */
}
error_codes;

Thanks for any suggestions,

Jerry