We should have a library-wide list of error codes, and an error message for each, and a function to return the error message for a code

[edwardhartnett]

As in netCDF, HDF5, HDF4, and many other projects, we should come up with a list of errror codes and error messages, and a function to return the message.

For example, in netcdf.h we have:

/** Not a netcdf id.

The specified netCDF ID does not refer to an
open netCDF dataset. */
#define	NC_EBADID	(-33)
#define	NC_ENFILE	(-34)	   /**< Too many netcdfs open */
#define	NC_EEXIST	(-35)	   /**< netcdf file exists && NC_NOCLOBBER */
#define	NC_EINVAL	(-36)	   /**< Invalid Argument */
#define	NC_EPERM	(-37)	   /**< Write to read only */

etc. There are many.

And also:

const char *nc_strerror(int ncerr1)
{

   /* If we're here, this is a netcdf error code. */
   switch(ncerr1)
   {
      case NC_NOERR:
	 return "No error";
      case NC_EBADID:
	 return "NetCDF: Not a valid ID";
      case NC_ENFILE:
	 return "NetCDF: Too many files open";
      case NC_EEXIST:
	 return "NetCDF: File exists && NC_NOCLOBBER";
      case NC_EINVAL:
	 return "NetCDF: Invalid argument";
      case NC_EPERM: