Simple demo of opening and reading data from a serial port in pure C in OS X.

OpenAndReceiveFromSerialPort.c

#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <dispatch/dispatch.h>

int main(int argc, char *argv[]) {
	int fd = open("/dev/cu.usbmodem1421", O_RDWR | O_NOCTTY | O_EXLOCK | O_NONBLOCK);
	if (fd < 1) { return printf("Error opening port: %i\n", errno); }
	
	struct termios originalPortAttributes;
	tcgetattr(fd, &originalPortAttributes); // Get original options so they can be reset later
	
	fcntl(fd, F_SETFL, 0);
	struct termios options;
		
	tcgetattr(fd, &options);
	
	cfmakeraw(&options);
	options.c_cc[VMIN] = 1; // Wait for at least 1 character before returning
	options.c_cc[VTIME] = 2; // Wait 200 milliseconds between bytes before returning from read
	
	// Set 8 data bits
	options.c_cflag &= ~CSIZE;
	options.c_cflag |= CS8;
	
	options.c_cflag &= ~PARENB; // Set no parity
	options.c_cflag &= ~CSTOPB; // 1 stop bit
	options.c_lflag &= ~ECHO; // no echo
	options.c_cflag &= ~CRTSCTS; // no RTS/CTS Flow Control
	options.c_cflag &= ~(CDTR_IFLOW | CDSR_OFLOW); // no DTR/DSR Flow Control
	options.c_cflag &= ~CCAR_OFLOW; // no DCD Flow Control
	
	options.c_cflag |= HUPCL; // Turn on hangup on close
	options.c_cflag |= CLOCAL; // Set local mode on
	options.c_cflag |= CREAD; // Enable receiver
	options.c_lflag &= ~(ICANON /*| ECHO*/ | ISIG); // Turn off canonical mode and signals
	
	// Set baud rate
	cfsetspeed(&options, B57600);
	
	if (tcsetattr(fd, TCSANOW, &options)) { return printf("Error setting options on port: %i\n", errno); }
	
	// Start a read dispatch source in the background
	dispatch_source_t readPollSource = dispatch_source_create(DISPATCH_SOURCE_TYPE_READ, fd, 0, dispatch_get_main_queue());
	dispatch_source_set_event_handler(readPollSource, ^{
		// Data is available
		char buf[1024] = {0};
		long lengthRead = read(fd, buf, sizeof(buf));
		if (lengthRead > 0) printf("received: %s\n", buf);
	});
	dispatch_source_set_cancel_handler(readPollSource, ^{ 
		// Set port back the way it was before we used it
		tcsetattr(fd, TCSADRAIN, &originalPortAttributes);
		printf("Closing port.\n");
		if (close(fd)) { printf("error closing port: %i", errno); return;}
		
		printf("Quitting.\n");
		exit(EXIT_SUCCESS);
	});
	dispatch_resume(readPollSource);
	
	dispatch_source_t stdinReadSource = dispatch_source_create(DISPATCH_SOURCE_TYPE_READ, STDIN_FILENO, 0, dispatch_get_main_queue());
	dispatch_source_set_event_handler(stdinReadSource, ^(void) {
		printf("got input\n");
		char buf[10] = {0};
		long lengthRead = read(STDIN_FILENO, buf, sizeof(buf));
		if (buf[0] == 'q') { dispatch_cancel(readPollSource); }
	});
	dispatch_resume(stdinReadSource);
	
	dispatch_main();
}