diff --git a/qse/include/qse/cmn/fio.h b/qse/include/qse/cmn/fio.h
index 972a0535..0dfb2ce1 100644
--- a/qse/include/qse/cmn/fio.h
+++ b/qse/include/qse/cmn/fio.h
@@ -60,13 +60,18 @@ enum qse_fio_open_flag_t
 	QSE_FIO_NOFOLLOW      = (1 << 15),
 
 	/* for WIN32 only. harmless(no effect) when used on other platforms */
-	QSE_FIO_NOSHRD        = (1 << 24),
-	QSE_FIO_NOSHWR        = (1 << 25),
-	QSE_FIO_NOSHDL        = (1 << 26),
+	QSE_FIO_NOSHRD        = (1 << 20),
+	QSE_FIO_NOSHWR        = (1 << 21),
+	QSE_FIO_NOSHDL        = (1 << 22),
 
 	/* hints to OS. harmless(no effect) when used on unsupported platforms */
-	QSE_FIO_RANDOM        = (1 << 27), /* hint that access be random */
-	QSE_FIO_SEQUENTIAL    = (1 << 28)  /* hint that access is sequential */
+	QSE_FIO_RANDOM        = (1 << 23), /* hint that access be random */
+	QSE_FIO_SEQUENTIAL    = (1 << 24)  /* hint that access is sequential */
+
+	/* NOTE:
+	 *   NEVER (1 << 31) since QSE_SIO_NOAUTOFLUSH is defined to 
+	 *   that value in sio.h FIO doesn't have any bufferring.
+	 */
 };
 
 enum qse_fio_std_t
diff --git a/qse/include/qse/cmn/sio.h b/qse/include/qse/cmn/sio.h
index 9ea57d39..e1379de6 100644
--- a/qse/include/qse/cmn/sio.h
+++ b/qse/include/qse/cmn/sio.h
@@ -53,7 +53,11 @@ enum qse_sio_open_flag_t
 	QSE_SIO_NOSHDL        = QSE_FIO_NOSHDL,
 
 	QSE_SIO_RANDOM        = QSE_FIO_RANDOM,
-	QSE_SIO_SEQUENTIAL    = QSE_FIO_SEQUENTIAL
+	QSE_SIO_SEQUENTIAL    = QSE_FIO_SEQUENTIAL,
+
+	/* Beware that this should not overlap with any QSE_FIO_XXXX.
+	 * See NOTE in fio.h */
+	QSE_SIO_NOAUTOFLUSH   = (1 << 31)
 };
 
 typedef qse_fio_off_t qse_sio_pos_t;
@@ -62,7 +66,7 @@ typedef qse_fio_std_t qse_sio_std_t;
 
 #define QSE_SIO_STDIN  QSE_FIO_STDIN
 #define QSE_SIO_STDOUT QSE_FIO_STDOUT
-#define QSE_SIO_STDER  QSE_FIO_STDERR
+#define QSE_SIO_STDERR QSE_FIO_STDERR
 
 /**
  * The qse_sio_t type defines a simple text stream over a file. It also
@@ -165,17 +169,37 @@ qse_ssize_t qse_sio_putc (
 	qse_char_t c
 );
 
-qse_ssize_t qse_sio_puts (
-	qse_sio_t*        sio,
-	const qse_char_t* str
+qse_ssize_t qse_sio_putms (
+	qse_sio_t*         sio,
+	const qse_mchar_t* str
 );
 
-qse_ssize_t qse_sio_putsn (
-	qse_sio_t*        sio, 
-	const qse_char_t* str,
-	qse_size_t        size
+qse_ssize_t qse_sio_putws (
+	qse_sio_t*         sio,
+	const qse_wchar_t* str
 );
 
+
+qse_ssize_t qse_sio_putmsn (
+	qse_sio_t*         sio, 
+	const qse_mchar_t* str,
+	qse_size_t         size
+);
+
+qse_ssize_t qse_sio_putwsn (
+	qse_sio_t*         sio, 
+	const qse_wchar_t* str,
+	qse_size_t         size
+);
+
+#if defined(QSE_CHAR_IS_MCHAR)
+#	define qse_sio_puts(sio,str) qse_sio_putms(sio,str)
+#	define qse_sio_putsn(sio,str,size) qse_sio_putmsn(sio,str,size)
+#else
+#	define qse_sio_puts(sio,str) qse_sio_putws(sio,str)
+#	define qse_sio_putsn(sio,str,size) qse_sio_putwsn(sio,str,size)
+#endif
+
 /**
  * The qse_sio_getpos() gets the current position in a stream.
  * Note that it may not return the desired postion due to buffering.
diff --git a/qse/lib/cmn/assert.c b/qse/lib/cmn/assert.c
index 076a1a27..06bf7ac9 100644
--- a/qse/lib/cmn/assert.c
+++ b/qse/lib/cmn/assert.c
@@ -23,7 +23,9 @@
 
 #ifndef NDEBUG
 
+#include <stdio.h>
 #include <qse/cmn/sio.h>
+#include "mem.h"
 
 #ifdef HAVE_EXECINFO_H
 #	include <execinfo.h>
@@ -43,14 +45,14 @@
 #	include "syscall.h"
 #endif
 
-#define NTOC(n) (QSE_T("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ")[n])
-#define WRITE_CHAR(c) \
+#define NTOC(n) (QSE_MT("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ")[n])
+#define WRITE_CHAR(sio,c) \
 do { \
-	qse_char_t __xxx_c = c; \
-	if (qse_sio_putsn (QSE_SIO_ERR, &__xxx_c, 1) != 1) return -1; \
+	qse_mchar_t __xxx_c = c; \
+	if (qse_sio_putmsn (sio, &__xxx_c, 1) != 1) return -1; \
 } while (0)
 
-static int write_num (qse_size_t x, int base)
+static int write_num (qse_sio_t* sio, qse_size_t x, int base)
 {
 	qse_size_t last = x % base;
 	qse_size_t y = 0; 
@@ -67,7 +69,7 @@ static int write_num (qse_size_t x, int base)
 
 	while (y > 0)
 	{
-		WRITE_CHAR (NTOC(y % base));
+		WRITE_CHAR (sio, NTOC(y % base));
 		y = y / base;
 		dig--;
 	}
@@ -75,9 +77,9 @@ static int write_num (qse_size_t x, int base)
 	while (dig > 0) 
 	{ 
 		dig--; 
-		WRITE_CHAR (QSE_T('0'));
+		WRITE_CHAR (sio, QSE_T('0'));
 	}
-	WRITE_CHAR (NTOC(last));
+	WRITE_CHAR (sio, NTOC(last));
 	return 0;
 }
 
@@ -90,38 +92,45 @@ void qse_assert_failed (
 	qse_size_t btsize, i;
 	char **btsyms;
 #endif
+	qse_sio_t* sio, siobuf;
 
-	qse_sio_puts (QSE_SIO_ERR, QSE_T("=[ASSERTION FAILURE]============================================================\n"));
+	sio = &siobuf;
+	if (qse_sio_initstd (sio, QSE_MMGR_GETDFL(), QSE_SIO_STDERR, QSE_SIO_NOAUTOFLUSH) <= -1) 
+		sio = QSE_SIO_ERR;
+
+	qse_sio_putms (sio, QSE_MT("=[ASSERTION FAILURE]============================================================\n"));
 
 #if 1
-	qse_sio_puts (QSE_SIO_ERR, QSE_T("                         __ \n"));
-	qse_sio_puts (QSE_SIO_ERR, QSE_T(" _____ _____ _____ _____|  |\n"));
-	qse_sio_puts (QSE_SIO_ERR, QSE_T("|     |     |  _  |   __|  |\n"));
-	qse_sio_puts (QSE_SIO_ERR, QSE_T("|  |  |  |  |   __|__   |__|\n"));
-	qse_sio_puts (QSE_SIO_ERR, QSE_T("|_____|_____|__|  |_____|__|\n"));
+	qse_sio_putms (sio, QSE_MT("                         __ \n"));
+	qse_sio_putms (sio, QSE_MT(" _____ _____ _____ _____|  |\n"));
+	qse_sio_putms (sio, QSE_MT("|     |     |  _  |   __|  |\n"));
+	qse_sio_putms (sio, QSE_MT("|  |  |  |  |   __|__   |__|\n"));
+	qse_sio_putms (sio, QSE_MT("|_____|_____|__|  |_____|__|\n"));
+	qse_sio_putms (sio, QSE_MT("                            \n"));
 #else
-	qse_sio_puts (QSE_SIO_ERR, QSE_T("                            __ \n"));
-	qse_sio_puts (QSE_SIO_ERR, QSE_T(" _____ _____ _____ _____   |  |\n"));
-	qse_sio_puts (QSE_SIO_ERR, QSE_T("|     |     |  _  |   __|  |  |\n"));
-	qse_sio_puts (QSE_SIO_ERR, QSE_T("|  |  |  |  |   __|__   |  |__|\n"));
-	qse_sio_puts (QSE_SIO_ERR, QSE_T("|_____|_____|__|  |_____|  |__|\n"));
+	qse_sio_putms (sio, QSE_MT("                            __ \n"));
+	qse_sio_putms (sio, QSE_MT(" _____ _____ _____ _____   |  |\n"));
+	qse_sio_putms (sio, QSE_MT("|     |     |  _  |   __|  |  |\n"));
+	qse_sio_putms (sio, QSE_MT("|  |  |  |  |   __|__   |  |__|\n"));
+	qse_sio_putms (sio, QSE_MT("|_____|_____|__|  |_____|  |__|\n"));
+	qse_sio_putms (sio, QSE_MT("                            __ \n"));
 #endif
 
-	qse_sio_puts (QSE_SIO_ERR, QSE_T("FILE "));
-	qse_sio_puts (QSE_SIO_ERR, file);
-	qse_sio_puts (QSE_SIO_ERR, QSE_T(" LINE "));
+	qse_sio_putms (sio, QSE_MT("FILE: "));
+	qse_sio_puts (sio, file);
+	qse_sio_putms (sio, QSE_MT(" LINE: "));
 
-	write_num (line, 10);
+	write_num (sio, line, 10);
 
-	qse_sio_puts (QSE_SIO_ERR, QSE_T(": "));
-	qse_sio_puts (QSE_SIO_ERR, expr);
-	qse_sio_puts (QSE_SIO_ERR, QSE_T("\n"));
+	qse_sio_putms (sio, QSE_MT("\nEXPRESSION: "));
+	qse_sio_puts (sio, expr);
+	qse_sio_putms (sio, QSE_MT("\n"));
 
 	if (desc != QSE_NULL)
 	{
-		qse_sio_puts (QSE_SIO_ERR, QSE_T("DESCRIPTION: "));
-		qse_sio_puts (QSE_SIO_ERR, desc);
-		qse_sio_puts (QSE_SIO_ERR, QSE_T("\n"));
+		qse_sio_putms (sio, QSE_MT("DESCRIPTION: "));
+		qse_sio_puts (sio, desc);
+		qse_sio_putms (sio, QSE_MT("\n"));
 	}
 
 #ifdef HAVE_BACKTRACE
@@ -129,30 +138,21 @@ void qse_assert_failed (
 	btsyms = backtrace_symbols (btarray, btsize);
 	if (btsyms != QSE_NULL)
 	{
-		qse_sio_puts (QSE_SIO_ERR, QSE_T("=[BACKTRACES]===================================================================\n"));
+		qse_sio_putms (sio, QSE_MT("=[BACKTRACES]===================================================================\n"));
 
 		for (i = 0; i < btsize; i++)
 		{
-			/* TODO:  call qse_sio_putms() instead of using ifdef */
-		#ifdef QSE_CHAR_IS_MCHAR
-			qse_sio_puts (QSE_SIO_ERR, btsyms[i]);
-		#else
-			qse_wchar_t wcs[256];
-			qse_size_t wcslen = QSE_COUNTOF(wcs);
-			qse_size_t mbslen;
-			qse_mbstowcs (btsyms[i], &mbslen, wcs, &wcslen);
-			wcs[QSE_COUNTOF(wcs) - 1] = QSE_T('\0');
-			qse_sio_puts (QSE_SIO_ERR, wcs);
-		#endif
-			qse_sio_puts (QSE_SIO_ERR, QSE_T("\n"));
+			qse_sio_putms (sio, btsyms[i]);
+			qse_sio_putms (sio, QSE_MT("\n"));
 		}
 
 		free (btsyms);
 	}
 #endif
 
-	qse_sio_puts (QSE_SIO_ERR, QSE_T("================================================================================\n"));
-	qse_sio_flush (QSE_SIO_ERR);
+	qse_sio_putms (sio, QSE_MT("================================================================================\n"));
+	qse_sio_flush (sio);
+	if (sio != QSE_SIO_ERR) qse_sio_fini (sio);
 
 #if defined(_WIN32)
 	ExitProcess (249);
diff --git a/qse/lib/cmn/sio.c b/qse/lib/cmn/sio.c
index 66839f72..481ad821 100644
--- a/qse/lib/cmn/sio.c
+++ b/qse/lib/cmn/sio.c
@@ -232,6 +232,7 @@ int qse_sio_init (
 	if (qse_fio_init (&sio->fio, mmgr, file, flags, mode) <= -1) return -1;
 
 	if (flags & QSE_SIO_IGNOREMBWCERR) topt |= QSE_TIO_IGNOREMBWCERR;
+	if (flags & QSE_SIO_NOAUTOFLUSH) topt |= QSE_TIO_NOAUTOFLUSH;
 
 	if (qse_tio_init(&sio->tio, mmgr, topt) <= -1)
 	{
@@ -315,25 +316,33 @@ qse_ssize_t qse_sio_putc (qse_sio_t* sio, qse_char_t c)
 	return qse_tio_write (&sio->tio, &c, 1);
 }
 
+#if 0
 qse_ssize_t qse_sio_puts (qse_sio_t* sio, const qse_char_t* str)
 {
 	return qse_tio_write (&sio->tio, str, (qse_size_t)-1);
 }
+#endif
 
-qse_size_t qse_sio_putms (qse_sio_t* sio, const qse_mchar_t* str)
+qse_ssize_t qse_sio_putms (qse_sio_t* sio, const qse_mchar_t* str)
 {
-	return qse_tio_write (&sio->tio, str, qse_mbslen(str));
+	return qse_tio_writem (&sio->tio, str, qse_mbslen(str));
 }
 
-qse_size_t qse_sio_putws (qse_sio_t* sio, const qse_wchar_t* str)
+qse_ssize_t qse_sio_putws (qse_sio_t* sio, const qse_wchar_t* str)
 {
-	return qse_tio_write (&sio->tio, str, qse_wcslen(str));
+	return qse_tio_writew (&sio->tio, str, qse_wcslen(str));
 }
 
-qse_ssize_t qse_sio_putsn (
-	qse_sio_t* sio, const qse_char_t* str, qse_size_t size)
+qse_ssize_t qse_sio_putmsn (
+	qse_sio_t* sio, const qse_mchar_t* str, qse_size_t size)
 {
-	return qse_tio_write (&sio->tio, str, size);
+	return qse_tio_writem (&sio->tio, str, size);
+}
+
+qse_ssize_t qse_sio_putwsn (
+	qse_sio_t* sio, const qse_wchar_t* str, qse_size_t size)
+{
+	return qse_tio_writew (&sio->tio, str, size);
 }
 
 int qse_sio_getpos (qse_sio_t* sio, qse_sio_pos_t* pos)
diff --git a/qse/lib/cmn/tio-put.c b/qse/lib/cmn/tio-put.c
index 8f72c7ec..bde319a3 100644
--- a/qse/lib/cmn/tio-put.c
+++ b/qse/lib/cmn/tio-put.c
@@ -199,6 +199,8 @@ qse_ssize_t qse_tio_writew (
 		wcnt = xwlen; mcnt = capa;
 
 		n = qse_wcsntombsn (wptr, &wcnt, &tio->outbuf[tio->outbuf_len], &mcnt);
+		tio->outbuf_len += mcnt;
+
 		if (n == -2)
 		{
 			/* the buffer is not large enough to 
@@ -234,10 +236,9 @@ qse_ssize_t qse_tio_writew (
 				for (i = 0; i < wcnt; i++)
 					if (wptr[i] == QSE_WT('\n')) nl = 1;
 			}
-		}
 
+		}
 		wptr += wcnt; xwlen -= wcnt;
-		tio->outbuf_len += mcnt;
 	}
 
 	if (nl && qse_tio_flush (tio) == -1) return -1;
diff --git a/qse/samples/cmn/str03.c b/qse/samples/cmn/str03.c
index efdaf8ea..a30b82f6 100644
--- a/qse/samples/cmn/str03.c
+++ b/qse/samples/cmn/str03.c
@@ -67,7 +67,7 @@ static int test1 (void)
 		qse_mbsset (buf, QSE_MT('A'), QSE_COUNTOF(buf));
 		n = qse_wcstombs (x[i], &wlen, buf, &mlen);
 
-		QSE_ASSERT (buf[QSE_COUNTOF(buf)-1] == QSE_MT('A'));
+		QSE_ASSERT (buf[QSE_COUNTOF(buf)-1] != QSE_MT('A'));
 		buf[QSE_COUNTOF(buf)-1] = QSE_MT('\0');
 
 		qse_printf (QSE_T("%s chars=%d bytes=%d [%hs]\n"),