diff --git a/qse/include/qse/awk/awk.h b/qse/include/qse/awk/awk.h
index ddd2c5f0..03aab016 100644
--- a/qse/include/qse/awk/awk.h
+++ b/qse/include/qse/awk/awk.h
@@ -2777,13 +2777,17 @@ QSE_EXPORT int qse_awk_rtx_valtoflt (
  * memory pointed to by \a l; A string containng '.', 'E', or 'e' is 
  * converted to a floating-pointer number and it is stored into memory
  * pointed to by \a r. If \a strict is 0, the function takes up to the last
- * valid character and never fails. If \a strict is non-zero, an invalid 
+ * valid character and never fails. If \a strict is 1, an invalid 
  * character causes the function to return an error.
  *
  * \return 0 if converted to an integer,
  *         1 if converted to a floating-point number
  *         -1 on error.
  */
+#define QSE_AWK_RTX_STRTONUM_MAKE_OPTION(strict,base) (((strict) & 1) | ((base) << 8))
+#define QSE_AWK_RTX_STRTONUM_GET_OPTION_STRICT(option) ((option) & 1)
+#define QSE_AWK_RTX_STRTONUN_GET_OPTION_BASE(option) ((option) >> 8)
+
 QSE_EXPORT int qse_awk_rtx_strtonum (
 	qse_awk_rtx_t*    rtx, /**< runtime context */
 	int               strict, /**< determines to perform strict check */
diff --git a/qse/lib/awk/mod-str.c b/qse/lib/awk/mod-str.c
index a074600d..8255cca8 100644
--- a/qse/lib/awk/mod-str.c
+++ b/qse/lib/awk/mod-str.c
@@ -29,6 +29,7 @@
 #include <qse/cmn/chr.h>
 #include "../cmn/mem-prv.h"
 #include "fnc.h"
+#include "val.h"
 
 static int fnc_normspace (qse_awk_rtx_t* rtx, const qse_awk_fnc_info_t* fi)
 {
@@ -215,6 +216,7 @@ static int fnc_value (qse_awk_rtx_t* rtx, const qse_awk_fnc_info_t* fi)
 static int fnc_tonum (qse_awk_rtx_t* rtx, const qse_awk_fnc_info_t* fi)
 {
 	/* str::tonum (value) */
+	/* str::tonum (string, base) */
 
 	qse_awk_val_t* retv;
 	qse_awk_val_t* a0;
@@ -224,18 +226,38 @@ static int fnc_tonum (qse_awk_rtx_t* rtx, const qse_awk_fnc_info_t* fi)
 
 	a0 = qse_awk_rtx_getarg(rtx, 0);
 
-	rx = qse_awk_rtx_valtonum (rtx, a0, &lv, &rv);
-	if (rx == 0)
+	if (QSE_AWK_RTX_GETVALTYPE(rtx, a0) == QSE_AWK_VAL_STR && qse_awk_rtx_getnargs(rtx) >= 2)
 	{
-		retv = qse_awk_rtx_makeintval (rtx, lv);
-	}
-	else if (rx >= 1)
-	{
-		retv = qse_awk_rtx_makefltval (rtx, rv);
+		/* if the value is known to be a string, it supports the optional
+		 * base parameter */
+		qse_awk_val_t* a1 = qse_awk_rtx_getarg(rtx, 1);
+		qse_awk_int_t base;
+
+		if (qse_awk_rtx_valtoint(rtx, a1, &base) <= -1) return -1;
+		rx = qse_awk_rtx_strtonum (
+			rtx,
+			QSE_AWK_RTX_STRTONUM_MAKE_OPTION(0, base),
+			((qse_awk_val_str_t*)a0)->val.ptr,
+			((qse_awk_val_str_t*)a0)->val.len,
+			&lv, &rv
+		);
 	}
 	else
 	{
-		retv = qse_awk_rtx_makeintval (rtx, 0);
+		rx = qse_awk_rtx_valtonum(rtx, a0, &lv, &rv);
+	}
+
+	if (rx == 0)
+	{
+		retv = qse_awk_rtx_makeintval(rtx, lv);
+	}
+	else if (rx >= 1)
+	{
+		retv = qse_awk_rtx_makefltval(rtx, rv);
+	}
+	else
+	{
+		retv = qse_awk_rtx_makeintval(rtx, 0);
 	}
 
 	if (!retv) return -1;
@@ -281,7 +303,7 @@ static fnctab_t fnctab[] =
 	{ QSE_T("sub"),       { { 2, 3, QSE_T("xvr") },  qse_awk_fnc_sub,       0 } },
 	{ QSE_T("substr"),    { { 2, 3, QSE_NULL },      qse_awk_fnc_substr,    0 } },
 	{ QSE_T("tolower"),   { { 1, 1, QSE_NULL },      qse_awk_fnc_tolower,   0 } },
-	{ QSE_T("tonum"),     { { 1, 1, QSE_NULL },      fnc_tonum,             0 } },
+	{ QSE_T("tonum"),     { { 1, 2, QSE_NULL },      fnc_tonum,             0 } },
 	{ QSE_T("toupper"),   { { 1, 1, QSE_NULL },      qse_awk_fnc_toupper,   0 } },
 	{ QSE_T("trim"),      { { 1, 1, QSE_NULL },      fnc_trim,              0 } },
 	{ QSE_T("value"),     { { 1, 1, QSE_NULL },      fnc_value,             0 } }
diff --git a/qse/lib/awk/run.c b/qse/lib/awk/run.c
index cbab4045..c74ff3df 100644
--- a/qse/lib/awk/run.c
+++ b/qse/lib/awk/run.c
@@ -4204,7 +4204,8 @@ static QSE_INLINE int __cmp_int_str (
 		qse_awk_flt_t rr;
 
 		n = qse_awk_rtx_strtonum (
-			rtx, 1, 
+			rtx,
+			QSE_AWK_RTX_STRTONUM_MAKE_OPTION(1, 0),
 			((qse_awk_val_str_t*)right)->val.ptr,
 			((qse_awk_val_str_t*)right)->val.len, 
 			&ll, &rr
diff --git a/qse/lib/awk/std.c b/qse/lib/awk/std.c
index 0ccdc566..aae6cf5c 100644
--- a/qse/lib/awk/std.c
+++ b/qse/lib/awk/std.c
@@ -2185,9 +2185,9 @@ static int fnc_setioattr (qse_awk_rtx_t* rtx, const qse_awk_fnc_info_t* fi)
 		qse_awk_flt_t r;
 		int x;
 
-		/* no error is returned by qse_awk_rtx_strnum() if the second 
-		 * parameter is 0. so i don't check for an error */
-		x = qse_awk_rtx_strtonum (rtx, 0, ptr[2], len[2], &l, &r);
+		/* no error is returned by qse_awk_rtx_strnum() if the strict option 
+		 * of the second parameter is 0. so i don't check for an error */
+		x = qse_awk_rtx_strtonum(rtx, QSE_AWK_RTX_STRTONUM_MAKE_OPTION(0, 0), ptr[2], len[2], &l, &r);
 		if (x == 0) r = (qse_awk_flt_t)l;
 
 		ioattr = find_or_make_ioattr (rtx, &rxtn->cmgrtab, ptr[0], len[0]);
diff --git a/qse/lib/awk/val.c b/qse/lib/awk/val.c
index 65a2fe0d..82c3bea0 100644
--- a/qse/lib/awk/val.c
+++ b/qse/lib/awk/val.c
@@ -443,8 +443,8 @@ qse_awk_val_t* qse_awk_rtx_makenstrvalwithxstr (qse_awk_rtx_t* rtx, const qse_cs
 	qse_awk_int_t l;
 	qse_awk_flt_t r;
 
-	x = qse_awk_rtx_strtonum (rtx, 1, str->ptr, str->len, &l, &r);
-	v = qse_awk_rtx_makestrvalwithxstr (rtx, str);
+	x = qse_awk_rtx_strtonum(rtx, QSE_AWK_RTX_STRTONUM_MAKE_OPTION(1, 0), str->ptr, str->len, &l, &r);
+	v = qse_awk_rtx_makestrvalwithxstr(rtx, str);
 
 	if (v == QSE_NULL) return QSE_NULL;
 
@@ -1555,7 +1555,8 @@ static int val_ref_to_num (
 			if (idx == 0)
 			{
 				return qse_awk_rtx_strtonum (
-					rtx, 0,
+					rtx, 
+					QSE_AWK_RTX_STRTONUM_MAKE_OPTION(0, 0),
 					QSE_STR_PTR(&rtx->inrec.line),
 					QSE_STR_LEN(&rtx->inrec.line),
 					l, r
@@ -1564,7 +1565,8 @@ static int val_ref_to_num (
 			else if (idx <= rtx->inrec.nflds)
 			{
 				return qse_awk_rtx_strtonum (
-					rtx, 0,
+					rtx,
+					QSE_AWK_RTX_STRTONUM_MAKE_OPTION(0, 0),
 					rtx->inrec.flds[idx-1].ptr,
 					rtx->inrec.flds[idx-1].len,
 					l, r
@@ -1573,7 +1575,7 @@ static int val_ref_to_num (
 			else
 			{
 				return qse_awk_rtx_strtonum (
-					rtx, 0, QSE_T(""), 0, l, r
+					rtx, QSE_AWK_RTX_STRTONUM_MAKE_OPTION(0, 0), QSE_T(""), 0, l, r
 				);
 			}
 		}
@@ -1628,7 +1630,8 @@ int qse_awk_rtx_valtonum (
 		case QSE_AWK_VAL_STR:
 		{
 			return qse_awk_rtx_strtonum (
-				rtx, 0,
+				rtx, 
+				QSE_AWK_RTX_STRTONUM_MAKE_OPTION(0, 0),
 				((qse_awk_val_str_t*)v)->val.ptr,
 				((qse_awk_val_str_t*)v)->val.len,
 				l, r
@@ -1691,15 +1694,18 @@ int qse_awk_rtx_valtoflt (
 }
 
 int qse_awk_rtx_strtonum (
-	qse_awk_rtx_t* rtx, int strict,
+	qse_awk_rtx_t* rtx, int option,
 	const qse_char_t* ptr, qse_size_t len, 
 	qse_awk_int_t* l, qse_awk_flt_t* r)
 {
 	const qse_char_t* endptr;
 	const qse_char_t* end;
 
+	int strict = QSE_AWK_RTX_STRTONUM_GET_OPTION_STRICT(option);
+	int base = QSE_AWK_RTX_STRTONUN_GET_OPTION_BASE(option);
+
 	end = ptr + len;
-	*l = qse_awk_strxtoint (rtx->awk, ptr, len, 0, &endptr);
+	*l = qse_awk_strxtoint(rtx->awk, ptr, len, base, &endptr);
 	if (endptr < end)
 	{
 		if (*endptr == QSE_T('.') || *endptr == QSE_T('E') || *endptr == QSE_T('e'))