writeCdf <- function(fname, cdfheader, cdf, cdfqc, overwrite=FALSE, verbose=0) {

     # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     # Consistency checks
     # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     if (length(cdf) != cdfheader$nunits) {

       stop("Number of units in 'cdf' does not match the number of units in the CDF header: ", length(cdf), " != ", cdfheader$nunits);

     }
 
     if (length(cdfqc) != cdfheader$nqcunits) {

       stop("Number of QC units in 'cdfqc' does not match the number of QC units in the CDF header: ", length(cdfqc), " != ", cdfheader$nqcunits);

     }
 
 

     if(verbose >= 1) {

       cat("Writing CDF file...\n");

       cat("  Pathname: ", fname, "\n", sep="");
     }
 

     if(file.exists(fname) && !overwrite)

       stop("Cannot write CDF: File already exists: ", fname);

     # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     # Figure out number of bytes per QC unit and regular unit

     # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     if (cdfheader$nqcunits > 0) {
       # Start positions for QC units
       lens <- lapply(cdfqc, FUN=.subset2, "ncells");
       lens <- unlist(lens, use.names=FALSE);
       lens <- 6 + 7*lens;
       qcUnitLengths <- lens;
     } else {
       qcUnitLengths <- NULL;
     }
 
     if (cdfheader$nunits > 0) {
       # Start positions for units

       # Number of bytes: 20 + (18+64)*nbrOfGroups + 14*totalNbrOfCells bytes

       lens <- lapply(cdf, FUN=function(unit) { 
         ncells <- .subset2(unit, "ncells");

         ngroups <- length(.subset2(unit, "groups"));
         20 + 82*ngroups + 14*ncells;

       })
       lens <- unlist(lens, use.names=FALSE);
       unitLengths <- lens;
     } else {
       unitLengths <- NULL;
     }

     # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     # Write CDF

     # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     # Open output connection
     con <- file(fname, open = "wb");
     on.exit(close(con));
 
     # Write CDF header
     writeCdfHeader(con=con, cdfheader, unitNames=names(cdf), 
                       qcUnitLengths=qcUnitLengths, unitLengths=unitLengths, 
                                                           verbose=verbose);
 
     # Write QC units
     writeCdfQcUnits(con=con, cdfqc, verbose=verbose);
 
     # Write regular units
     writeCdfUnits(con=con, cdf, verbose=verbose);

     if(verbose >= 1)

       cat("Writing CDF file...done\n");

     invisible(NULL);

 } # writeCdf()
 

 ############################################################################
 # HISTORY:

 # 2012-05-18
 # o Now using stop() instead of throw().

 # 2007-01-10 /HB
 # o Added writeCdfHeader(), writeCdfQcUnits() and writeCdfUnits().  With
 #   these it is now possible to build up the CDF in chunks.
 # o Removed obsolete arguments 'addName' and 'addPositions' and all related
 #   code.  Internal variable 'positions' is not needed anymore. 
 #   There are no more seek():s in the code.
 # o Removed obsolete .writeCdfUnit2().
 # o Now only every 1000th unit (instead of 100th) is reported. It is now
 #   also a count down.

 # 2006-12-18 /KS
 # o Make global replacement "block" -> "group" to maintain consistency
 #   with other code, pursuant to communication from KH.

 # 2006-10-25 /HB (+KS)
 # o BUG FIX: .initializeCdf() was writing false file offset for QC units
 #   when the number QC nunits were zero.  This would core dump readCdfNnn().

 # 2006-09-21 /HB
 # o BUG FIX: The 'atom' and 'indexpos' fields were swapped.
 # o Now suppressing warnings "writeChar: more characters requested..." in
 #   writeCdf().

 # 2006-09-11 /HB
 # o BUG FIX: nrows & ncols were swapped in the CDF header.

 # 2006-09-09 /HB
 # o Updated writeCdf() has been validate with compareCdfs() on a few arrays.
 # o With the below "optimizations" writeCdf() now writes Hu6800.CDF with
 #   units in 130s compared to 140s.
 # o Now initializeCdf() dumps all unit names at once by first building a
 #   raw vector.  This is now much faster than before.
 # o Now writeCdf() does not seek() around in the file anymore.  This should
 #   speed up writing at least a bit.
 # o Made some optimization, which speeds up the writing a bit.  Jumping
 #   around in the file with seek() is expensive and should be avoided.
 # o Rename writeUnit() to writeCdfUnit() and same for the QC function.
 # o Added more verbose output and better errror messages for writeCdf().

 # 2006-09-07 /HB
 # o Maybe initalizeCdf(), writeUnit(), and writeQcUnit() should be made
 #   private functions of this package.
 # o Removed textCdf2binCdf() skeleton. See convertCdf() instead.
 # o Updated writeCdf() such that the connection is guaranteed to be closed
 #   regardless.
 ############################################################################