NCL Home > Documentation > Functions > Metadata routines


Returns True if the given dimension name is defined as unlimited on the given file.


	function isunlimited (
		thefile  [1] : file,    
		dim_name [1] : string   

	return_val [dimsizes] :  logical



Reference to a file opened with addfile or addfiles.


Named dimension to check for being set to unlimited.


For the named dim_name dimension, isunlimited returns True if dim_name is defined as an unlimited dimension on the file thefile, and False otherwise. If thefile is not a valid file, or if dim_name is not a named dimension on the file, then a value of False is returned.

An unlimited dimension is sometimes known as a record dimension. A variable with an unlimited dimension can grow to any length along that dimension. The unlimited dimension index is like a record number in conventional record-oriented files. A file can have at most one unlimited dimension (this may change in the future).


Consider a netCDF file where "ncdump -h" yields:

netcdf sstdata_netcdf {
    longitude = 181 ;
    latitude = 91 ;
    time = UNLIMITED ; // (12 currently)
    float sst(time, latitude, longitude) ;
        sst:valid_range = -1.8f, 35.f ;
        sst:units = "deg_C" ;
        sst:_FillValue = -999.f ;
    float time(time) ;
        time:valid_range = 1.f, 12.f ;
        time:units = "Month" ;
        time:long_name = "Time" ;
    float lat(latitude) ;
        lat:units = "degrees_north" ;
        lat:long_name = "Latitude" ;
    float lon(longitude) ;
        lon:units = "degrees_east" ;
        lon:long_name = "Longitude" ;
To determine if the named dimension time in the file is unlimited, you can use the following code snippet:
   f      = addfile ("$NCARG_ROOT/lib/ncarg/data/cdf/" , "r")
   if (isunlimited(f, "time"))  
       ... ; True
       ... ; False
   end if