Question

Firstly, what is DSUSP?

I’m trying to disable it using the following code line:

tntty.c_cc[VDSUSP] = _POSIX_VDISABLE;  

But I get the error that “VDSUSP is undeclared”

Answer 1

The Linux termios(3) man page describes it thus (emphasis mine):

VDSUSP (not in POSIX; not supported under Linux; 031, EM,
Ctrl-Y) Delayed suspend character: send SIGTSTP signal when the
character is read by the user program. Recognized when IEXTEN
and ISIG are set, and the system supports job control, and then not
passed as input.

As this isn’t a POSIX-specified index, you should test for its presence and only attempt to disable it on platforms where it is defined:

#ifdef VDSUSP
tntty.c_cc[VDSUSP] = _POSIX_VDISABLE;  
#endif