termios : a prelude to serial port programming

If you like to make a serial port program, you need to use functions and structures declared inside /usr/include/termios.h (be aware it uses another header file /usr/include/bits/termios.h). The first thing that you need to understand is a data structure declared inside /usr/include/bits/termios.h :
struct termios
{
tcflag_t c_iflag; /* input mode flags */
tcflag_t c_oflag; /* output mode flags */
tcflag_t c_cflag; /* control mode flags */
tcflag_t c_lflag; /* local mode flags */
cc_t c_line; /* line discipline */
cc_t c_cc[NCCS]; /* control characters */
speed_t c_ispeed; /* input speed */
speed_t c_ospeed; /* output speed */
#define _HAVE_STRUCT_TERMIOS_C_ISPEED 1
#define _HAVE_STRUCT_TERMIOS_C_OSPEED 1
};

Inside that structure we see the names of other types : tcflag_t, cc_t, and speed_t. What they really are of type char and unsigned int :
1.typedef unsigned char cc_t;
2.typedef unsigned int speed_t;
3.typedef unsigned int tcflag_t;

Now lets disect what are inside the termios (These values are declared inside /usr/include/bits/termios.h) :
1. The posibble values for c_iflag
/* c_iflag bits */
#define IGNBRK 0000001
#define BRKINT 0000002
#define IGNPAR 0000004
#define PARMRK 0000010
#define INPCK 0000020
#define ISTRIP 0000040
#define INLCR 0000100
#define IGNCR 0000200
#define ICRNL 0000400
#define IUCLC 0001000
#define IXON 0002000
#define IXANY 0004000
#define IXOFF 0010000
#define IMAXBEL 0020000
#define IUTF8 0040000

2. The possible values for c_oflag :
/* c_oflag bits */
#define OPOST 0000001
#define OLCUC 0000002
#define ONLCR 0000004
#define OCRNL 0000010
#define ONOCR 0000020
#define ONLRET 0000040
#define OFILL 0000100
#define OFDEL 0000200
#if defined __USE_MISC || defined __USE_XOPEN
# define NLDLY 0000400
# define NL0 0000000
# define NL1 0000400
# define CRDLY 0003000
# define CR0 0000000
# define CR1 0001000
# define CR2 0002000
# define CR3 0003000
# define TABDLY 0014000
# define TAB0 0000000
# define TAB1 0004000
# define TAB2 0010000
# define TAB3 0014000
# define BSDLY 0020000
# define BS0 0000000
# define BS1 0020000
# define FFDLY 0100000
# define FF0 0000000
# define FF1 0100000
#endif
#define VTDLY 0040000
#define VT0 0000000
#define VT1 0040000
#ifdef __USE_MISC
# define XTABS 0014000
#endif

3. The possible values for c_cflag :
/* c_cflag bit meaning */
#ifdef __USE_MISC
# define CBAUD 0010017
#endif
#define B0 0000000 /* hang up */
#define B50 0000001
#define B75 0000002
#define B110 0000003
#define B134 0000004
#define B150 0000005
#define B200 0000006
#define B300 0000007
#define B600 0000010
#define B1200 0000011
#define B1800 0000012
#define B2400 0000013
#define B4800 0000014
#define B9600 0000015
#define B19200 0000016
#define B38400 0000017
#ifdef __USE_MISC
# define EXTA B19200
# define EXTB B38400
#endif
#define CSIZE 0000060
#define CS5 0000000
#define CS6 0000020
#define CS7 0000040
#define CS8 0000060
#define CSTOPB 0000100
#define CREAD 0000200
#define PARENB 0000400
#define PARODD 0001000
#define HUPCL 0002000
#define CLOCAL 0004000
#ifdef __USE_MISC
# define CBAUDEX 0010000
#endif
#define B57600 0010001
#define B115200 0010002
#define B230400 0010003
#define B460800 0010004
#define B500000 0010005
#define B576000 0010006
#define B921600 0010007
#define B1000000 0010010
#define B1152000 0010011
#define B1500000 0010012
#define B2000000 0010013
#define B2500000 0010014
#define B3000000 0010015
#define B3500000 0010016
#define B4000000 0010017
#define __MAX_BAUD B4000000
#ifdef __USE_MISC
# define CIBAUD 002003600000 /* input baud rate (not used) */
# define CMSPAR 010000000000 /* mark or space (stick) parity */
# define CRTSCTS 020000000000 /* flow control */
#endif


4. The possible values for c_lflag :
/* c_lflag bits */
#define ISIG 0000001
#define ICANON 0000002
#if defined __USE_MISC || defined __USE_XOPEN
# define XCASE 0000004
#endif
#define ECHO 0000010
#define ECHOE 0000020
#define ECHOK 0000040
#define ECHONL 0000100
#define NOFLSH 0000200
#define TOSTOP 0000400
#ifdef __USE_MISC
# define ECHOCTL 0001000
# define ECHOPRT 0002000
# define ECHOKE 0004000
# define FLUSHO 0010000
# define PENDIN 0040000
#endif
#define IEXTEN 0100000