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(libc.info)Setting Modes

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Setting Terminal Modes Properly
-------------------------------

   When you set terminal modes, you should call `tcgetattr' first to
get the current modes of the particular terminal device, modify only
those modes that you are really interested in, and store the result with
`tcsetattr'.

   It's a bad idea to simply initialize a `struct termios' structure to
a chosen set of attributes and pass it directly to `tcsetattr'.  Your
program may be run years from now, on systems that support members not
documented in this manual.  The way to avoid setting these members to
unreasonable values is to avoid changing them.

   What's more, different terminal devices may require different mode
settings in order to function properly.  So you should avoid blindly
copying attributes from one terminal device to another.

   When a member contains a collection of independent flags, as the
`c_iflag', `c_oflag' and `c_cflag' members do, even setting the entire
member is a bad idea, because particular operating systems have their
own flags.  Instead, you should start with the current value of the
member and alter only the flags whose values matter in your program,
leaving any other flags unchanged.

   Here is an example of how to set one flag (`ISTRIP') in the `struct
termios' structure while properly preserving all the other data in the
structure:

     int
     set_istrip (int desc, int value)
     {
       struct termios settings;
       int result;
     
       result = tcgetattr (desc, &settings);
       if (result < 0)
         {
           perror ("error in tcgetattr");
           return 0;
         }
       settings.c_iflag &= ~ISTRIP;
       if (value)
         settings.c_iflag |= ISTRIP;
       result = tcsetattr (desc, TCSANOW, &settings);
       if (result < 0)
         {
           perror ("error in tcgetattr");
           return;
        }
       return 1;
     }