1 files changed, 45 insertions, 0 deletions
diff --git a/src/stdio/ungetwc.c b/src/stdio/ungetwc.c
new file mode 100644
index 00000000..f7cde2e0
--- /dev/null
+++ b/src/stdio/ungetwc.c
@@ -0,0 +1,45 @@
+#include "stdio_impl.h"
+
+wint_t ungetwc(wint_t c, FILE *f)
+{
+	unsigned char mbc[MB_LEN_MAX];
+	int l=1;
+
+	if (c == WEOF) return c;
+
+	/* Try conversion early so we can fail without locking if invalid */
+	if (!isascii(c) && (l = wctomb(mbc, c)) < 0)
+		return WEOF;
+
+	FLOCK(f);
+
+	f->mode |= f->mode+1;
+
+	/* Fail if unreadable or writing and unable to flush */
+	if ((f->flags & (F_ERR|F_NORD)) || (f->wpos && __oflow(f))) {
+		FUNLOCK(f);
+		return EOF;
+	}
+
+	/* Clear write mode */
+	f->wpos = f->wstop = f->wend = 0;
+
+	/* Put the file in read mode */
+	if (!f->rpos) f->rpos = f->rend = f->buf;
+
+	/* If unget buffer is nonempty, fail. */
+	if (f->rpos < f->buf) {
+		FUNLOCK(f);
+		return WEOF;
+	}
+
+	/* Put character back into the buffer */
+	if (isascii(c)) *--f->rpos = c;
+	else memcpy(f->rpos -= l, mbc, l);
+
+	/* Clear EOF */
+	f->flags &= ~F_EOF;
+
+	FUNLOCK(f);
+	return c;
+}