DH> I want to write program to use the modem and serial port.
  ofstream modem("COM1", ios::out|ios::binary) ;
  modem << "ATZ\r" << flush ;
You didn't specify an operating system, but this approach works for just 
about all PC operating systems.  Raw MS-DOS/PC-DOS will not do 
interrupt-driven comms.  However, DOS applications that use the above 
technique will run well, and *will* take advantage of interrupt-driven comms, 
albeit unknowingly, when run on operating systems like OS/2 Warp.
 ¯ JdeBP ®
--- FleetStreet 1.19 NR
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