writerune() should operate on a FILE *

libutf/writerune.c

@@ -7,16 +7,16 @@
 #include "../utf.h"
 
 void
-writerune(Rune *r)
+writerune(const char *file, FILE *fp, Rune *r)
 {
 	char buf[UTFmax];
 	int n;
 
 	if ((n = runetochar(buf, r)) > 0) {
-		fwrite(buf, n, 1, stdout);
-		if (ferror(stdout)) {
-			fprintf(stderr, "stdout: write error: %s\n",
-				strerror(errno));
+		fwrite(buf, n, 1, fp);
+		if (ferror(fp)) {
+			fprintf(stderr, "%s: write error: %s\n",
+				file, strerror(errno));
 			exit(1);
 		}
 	}