title: datatable.integer64 argument is not working for me should it?
body: <p>I am trying to load <code>integer64</code> as <code>character</code> in <code>fread</code> <code>?fread</code> indicates that the <code>integer64</code> argument is not implemented but the <code>options(datatable.integer64)</code> is. Though fread keeps loading as <code>int64</code>.</p>
  
  <p>How can I tell <code>fread</code> to load as <code>character</code>. <strong>EDIT</strong> [If <code>colClasses</code> is the answer, I think it does not allow to specify a single column name or index and the table I load has tens of columns so unpracticable... => This was WRONG]</p>
  
  <p>Here is a sample</p>
  
  <pre><code>#for int 64
  library(bit64)
  #for fast everything
  library(data.table)
  
  #here is a sample
  df &lt;- structure(list(IDFD = structure(c(5.13878419797985e-299, 5.13878419797985e-299, 
  + 5.13878419797985e-299, 5.13878419797987e-299, 5.13878419797987e-299, 
  + 5.13878419797987e-299, 5.13878419797987e-299, 5.13878419797987e-299, 
  + 5.13878419797988e-299, 5.13878419797988e-299), class = "integer64")), .Names = "IDFD", row.names = c(NA, 
  + -10L), class = c("data.table", "data.frame"))
  #write the sample to file
  write.csv(df,"test.csv",quote=F,row.names=F)
  
  #I can't load it as characters
  options(datatable.integer64='character')
  str(fread("test.csv",integer64='character'))
  Classes ‘data.table’ and 'data.frame':  10 obs. of  1 variable:
   $ IDFD:Class 'integer64'  num [1:10] 5.14e-299 5.14e-299 5.14e-299 5.14e-299 5.14e-299 ...
  </code></pre>