Low level interface function to the IBM ILOG CPLEX function
  CPXfputs. Consult the IBM ILOG CPLEX documentation for
  more detailed information. This funtion has no functionality
  from IBM ILOG CPLEX >= 12.9.0 on, where CPXfputs has
  been removed.
fileputCPLEX(cpfile, stuff = "")A pointer to a file as returned by openFileCPLEX.
A character string to be written to the file.
A nonnegative value if successful, otherwise EOF.
Interface to the C function fileput which calls the CPLEX
  function CPXfputs.
The IBM ILOG CPLEX home page at https://www.ibm.com/support/knowledgecenter/SSSA5P.