diff --git a/libc/Makefile b/libc/Makefile
index 0ef66759..267ed0a3 100644
--- a/libc/Makefile
+++ b/libc/Makefile
@@ -142,6 +142,7 @@ wcslen.o \
wcsncat.o \
wcsncpy.o \
wcsrchr.o \
+wcsrtombs.o \
wcsspn.o \
wcstok.o \
wctomb.o \
diff --git a/libc/include/wchar.h b/libc/include/wchar.h
index 7e784baa..c2333f22 100644
--- a/libc/include/wchar.h
+++ b/libc/include/wchar.h
@@ -74,6 +74,7 @@ size_t wcslen(const wchar_t*);
wchar_t* wcsncat(wchar_t* restrict, const wchar_t* restrict, size_t);
wchar_t* wcsncpy(wchar_t* restrict, const wchar_t* restrict, size_t);
wchar_t* wcsrchr(const wchar_t*, wchar_t);
+size_t wcsrtombs(char* restrict, const wchar_t** restrict, size_t, mbstate_t* restrict);
size_t wcsspn(const wchar_t*, const wchar_t*);
wchar_t* wcstok(wchar_t* restrict, const wchar_t* restrict, wchar_t** restrict);
@@ -108,7 +109,6 @@ long long wcstoll(const wchar_t* restrict, wchar_t** restrict, int);
long wcstol(const wchar_t* restrict, wchar_t** restrict, int);
size_t mbrlen(const char* restrict, size_t, mbstate_t* restrict);
size_t wcsftime(wchar_t* restrict, size_t, const wchar_t* restrict, const struct tm* restrict);
-size_t wcsrtombs(char* restrict, const wchar_t** restrict, size_t, mbstate_t* restrict);
size_t wcsxfrm(wchar_t* restrict, const wchar_t* restrict, size_t);
unsigned long long wcstoull(const wchar_t* restrict, wchar_t** restrict, int);
unsigned long wcstoul(const wchar_t* restrict, wchar_t** restrict, int);
diff --git a/libc/wcsrtombs.cpp b/libc/wcsrtombs.cpp
new file mode 100644
index 00000000..2b3db50f
--- /dev/null
+++ b/libc/wcsrtombs.cpp
@@ -0,0 +1,76 @@
+/*******************************************************************************
+
+ Copyright(C) Jonas 'Sortie' Termansen 2013.
+
+ This file is part of the Sortix C Library.
+
+ The Sortix C Library is free software: you can redistribute it and/or modify
+ it under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or (at your
+ option) any later version.
+
+ The Sortix C Library is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with the Sortix C Library. If not, see .
+
+ wcsrtombs.cpp
+ Convert a wide-character string to multibyte string.
+
+*******************************************************************************/
+
+#include
+#include
+#include
+#include
+#include
+
+extern "C" size_t wcsrtombs(char* dst, const wchar_t** src_ptr, size_t dst_len,
+ mbstate_t* ps)
+{
+ assert(src_ptr && *src_ptr);
+ // Avoid changing *src_ptr if dst is NULL.
+ const wchar_t* local_src_ptr = *src_ptr;
+ if ( !dst )
+ src_ptr = &local_src_ptr;
+ // For some reason, the standards don't mandate that the secret ps variable
+ // is reset when ps is NULL, unlike mbstowcs that always resets this
+ // variable. We'll avoid resetting the variable here in case any programs
+ // actually take advantage of this fact.
+ static mbstate_t static_ps;
+ if ( !ps )
+ ps = &static_ps;
+ size_t ret = 0;
+ size_t src_len = wcslen(*src_ptr);
+ char buf[MB_CUR_MAX];
+ while ( !dst || dst_len )
+ {
+ mbstate_t saved_ps = *ps;
+ size_t produced = wcrtomb(buf, **src_ptr, ps);
+ if ( produced == (size_t) -1 )
+ return (size_t) -1;
+ if ( dst && dst_len < produced )
+ {
+ *ps = saved_ps;
+ break;
+ }
+ memcpy(dst, buf, produced);
+ if ( **src_ptr == L'\0' )
+ {
+ ret += produced - 1; // Don't count the '\0' byte.
+ *src_ptr = NULL;
+ break;
+ }
+ ret += produced;
+ (*src_ptr)++;
+ src_len--;
+ if ( dst )
+ dst += produced,
+ dst_len -= produced;
+ ret++;
+ }
+ return ret;
+}