check_utf8.c

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <termios.h>
#include <fcntl.h>

#define EXIT_FAILURE 1

int
check_utf8() {
	int supports_utf8 = 0;

	struct termios original;
	/* store current tty settings */
	if (tcgetattr(STDIN_FILENO, &original) == -1) {
		perror("check_utf8 get terminal settings");
		exit(EXIT_FAILURE);
	}

	/* set minimal raw mode */
	struct termios raw;
	raw.c_iflag &= ~(ISTRIP | BRKINT | INPCK | IGNCR | INLCR | ICRNL | IXON | IXOFF | PARMRK);
	raw.c_cflag &= ~PARENB;
	raw.c_cflag |= CS8;
	raw.c_lflag &= ~(ECHO | ICANON | IEXTEN | ISIG);
	raw.c_cc[VMIN] = 0;
	raw.c_cc[VTIME] = 3; /* timeout of 0.3 seconds */
	raw.c_oflag &= ~(OPOST | OCRNL | ONLRET);
	tcflush(STDIN_FILENO, TCIFLUSH);
	if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &raw) == -1) {
		perror("check_utf8 set raw mode");
		exit(EXIT_FAILURE);
	}

	/* output the non-breaking space character twice in raw UTF-8 */
	if (write(STDOUT_FILENO, "\r\n\xc2\xa0\xc2\xa0", 6) != 6) {
		perror("check_utf8 test sequence");
		exit(EXIT_FAILURE);
	}
	/* request the terminal to report the cursor position */
	if (write(STDOUT_FILENO, "\x1b[6n", 4) != 4) {
		perror("check_utf8 cursor position");
		exit(EXIT_FAILURE);
	}
	tcdrain(STDOUT_FILENO);

	/* parse terminal reply */
	char c, previous_char = '\0';
	while (read(STDIN_FILENO, &c, 1) == 1) {
		printf("-%c-\n", c);
		/* skip everything until the row column separator */
		if (previous_char == ';') {
			/* column == 3 means UTF-8 is supported,
			 * non-supporting terminals will report the cursor position
			 * in column 5 */
			supports_utf8 = c == '3' ? 1 : 0;

			/* disable read timeout */
			raw.c_cc[VTIME] = 0;
			if (tcsetattr(STDIN_FILENO, TCSANOW, &raw) == -1) {
				perror("check_utf8_console after test");
				//exit(EXIT_FAILURE);
			}
		}
		previous_char = c;
	}

	/* restore previous terminal settings */
	if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &original) == -1) {
		perror("check_utf8_console restore terminal settings");
		exit(EXIT_FAILURE);
	}

	return supports_utf8;
}

int main() {
	if (check_utf8()) {
		printf("\nUTF-8 supported \xf0\x9f\x92\xa9\n");
	} else {
		printf("\nUTF-8 not supported :-(\n");
	}
}