wcstombs — convert a wide-character string to a multibyte string


        #include <stdlib.h>
size_t wcstombs( char *dest,
  const wchar_t *src,
  size_t n);


If dest is not NULL, the wcstombs() function converts the wide-character string src to a multibyte string starting at dest. At most n bytes are written to dest. The conversion starts in the initial state. The conversion can stop for three reasons:

  1. A wide character has been encountered that can not be represented as a multibyte sequence (according to the current locale). In this case, (size_t) −1 is returned.

  2. The length limit forces a stop. In this case, the number of bytes written to dest is returned, but the shift state at this point is lost.

  3. The wide-character string has been completely converted, including the terminating null wide character (L'\0'). In this case, the conversion ends in the initial state. The number of bytes written to dest, excluding the terminating null byte ('\0'), is returned.

The programmer must ensure that there is room for at least n bytes at dest.

If dest is NULL, n is ignored, and the conversion proceeds as above, except that the converted bytes are not written out to memory, and no length limit exists.

In order to avoid the case 2 above, the programmer should make sure n is greater than or equal to wcstombs(NULL,src,0)+1.


The wcstombs() function returns the number of bytes that make up the converted part of a multibyte sequence, not including the terminating null byte. If a wide character was encountered which could not be converted, (size_t) −1 is returned.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
wcstombs() Thread safety MT-Safe


POSIX.1-2001, POSIX.1-2008, C99.


The behavior of wcstombs() depends on the LC_CTYPE category of the current locale.

The function wcsrtombs(3) provides a thread safe interface to the same functionality.


mblen(3), mbtowc(3), mbstowcs(3), wcsrtombs(3) wctom(3)


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  Copyright (c) Bruno Haible <>

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References consulted:
  GNU glibc-2 source code and manual
  Dinkumware C library reference
  OpenGroup's Single UNIX specification
  ISO/IEC 9899:1999