How do I read data from serial port in Linux using C?

Question

I am new to serial programming in Linux using C. I have found a small piece of code to write data on serial port which I am sharing here. After running this code I may assum

Answer 1

In theory, all you have to do is open the relevant port for reading, and use read() to get the data.

int
read_port(void)
{
    int fd = open("/dev/ttyS0", O_RDONLY | O_NOCTTY);
    if (fd == -1)
    {
        /* Could not open the port. */
        perror("open_port: Unable to open /dev/ttyS0 - ");
    }

    char buffer[32];
    int n = read(fd, buffer, sizeof(buffer));
    if (n < 0)
        fputs("read failed!\n", stderr);
    return (fd);
}

There are differences; notably, the read needs a buffer to put the data in. The code shown discards the first message read. Note that a short read simply indicates that there was less data available than requested at the time when the read completed. It does not automatically indicate an error. Think of a command line; some commands might be one or two characters (ls) where others might be quite complex (find /some/where -name '*.pdf' -mtime -3 -print). The fact that the same buffer is used to read both isn't a problem; one read gives 3 characters (newline is included), the other 47 or so.

Answer 2

The program posted makes a lot of assumptions about the state of the port. In a real world application you should do all the important setup explicitly. I think the best source for learning serial port programming under POSIX is the

Serial Programming Guide for POSIX Operating Systems

I'm mirroring it here: https://www.cmrr.umn.edu/~strupp/serial.html