find_first_utf8_char.c

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, const char *argv[])
{
	FILE *fp;
	int c;
	unsigned int lineno = 1, colno = 1;

	if (argc != 2) {
		fprintf(stderr, "Usage: %s file\n", argv[0]);
		exit(EXIT_FAILURE);
	}
	fp = fopen(argv[1], "r");
	if (fp == NULL) {
		fprintf(stderr, "%s: error: %s\n", argv[0], strerror(errno));
		exit(EXIT_FAILURE);
	}
	for (;;) {
		c = fgetc(fp);
		if (c == EOF) {
			fprintf(stderr, "None found. Entire file is ASCII.\n");
			exit(EXIT_FAILURE);
		}
		if ((unsigned char) c >> 7 == 1) {
			fprintf(stderr, "Found UTF-8 character at %s:%u:%u\n",
					argv[1], lineno, colno);
			exit(EXIT_SUCCESS);
		}
		if (c == '\n') {
			colno = 1;
			lineno++;
		}
		colno++;
	}
}