the function "netcdf.getAtt" don't work on my nc files, is it a bug?

I use the function netcdf.getAtt for my nc files, but I get the error that the datatype ( 12 ) of the attribute is unsupported, then I find the value of xtype is 12 which is returned by the function netcdflib, in fact, that attribute is the string type but the length is variable. So, matlab cann't read this kind of attribute whose data type is variable length, is it so?