--- name: "vfwprintf" section: "3" platform: "linux" package: "man-pages" version: "6.19-1" release: "Arch Linux 2026-11-01" platforms: ["linux", "freebsd"] url: "https://new.carta.tech/wprintf" --- # vfwprintf(3) formatted wide-character output conversion Part of [wprintf(3)](/wprintf/3.md). ## NAME wprintf, fwprintf, swprintf, vwprintf, vfwprintf, vswprintf - formatted wide-character output conversion ## LIBRARY Standard C library (*libc*, *-lc*) ## SYNOPSIS ``` #include #include ``` **int wprintf(const wchar\_t \*restrict** *format***, ...);** **int fwprintf(FILE \*restrict** *stream***,** **const wchar\_t \*restrict** *format***, ...);** **int swprintf(**size\_t n; **wchar\_t** *wcs***\[restrict** *n***\], size\_t** *n***,** **const wchar\_t \*restrict** *format***, ...);** **int vwprintf(const wchar\_t \*restrict** *format***, va\_list** *args***);** **int vfwprintf(FILE \*restrict** *stream***,** **const wchar\_t \*restrict** *format***, va\_list** *args***);** **int vswprintf(**size\_t n; **wchar\_t** *wcs***\[restrict** *n***\], size\_t** *n***,** **const wchar\_t \*restrict** *format***, va\_list** *args***);** Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)): All functions shown above: ``` _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L ``` ## DESCRIPTION The **wprintf**() family of functions is the wide-character equivalent of the [**printf**(3)](/printf/3.md) family of functions. It performs formatted output of wide characters. The **wprintf**() and **vwprintf**() functions perform wide-character output to *stdout*. *stdout* must not be byte oriented; see [**fwide**(3)](/fwide/3.md) for more information. The **fwprintf**() and **vfwprintf**() functions perform wide-character output to *stream*. *stream* must not be byte oriented; see [**fwide**(3)](/fwide/3.md) for more information. The **swprintf**() and **vswprintf**() functions perform wide-character output to an array of wide characters. The programmer must ensure that there is room for at least *n* wide characters at *wcs*. These functions are like the [**printf**(3)](/printf/3.md), [**vprintf**(3)](/vprintf/3.md), [**fprintf**(3)](/fprintf/3.md), [**vfprintf**(3)](/vfprintf/3.md), [**sprintf**(3)](/sprintf/3.md), [**vsprintf**(3)](/vsprintf/3.md) functions except for the following differences: - **•** The *format* string is a wide-character string. - **•** The output consists of wide characters, not bytes. - **•** **swprintf**() and **vswprintf**() take a *n* argument, [**sprintf**(3)](/sprintf/3.md) and [**vsprintf**(3)](/vsprintf/3.md) do not. ([**snprintf**(3)](/snprintf/3.md) and [**vsnprintf**(3)](/vsnprintf/3.md) take a *n* argument, but these functions do not return -1 upon buffer overflow on Linux.) The treatment of the conversion characters **c** and **s** is different: - **c** If no **l** modifier is present, the *int* argument is converted to a wide character by a call to the [**btowc**(3)](/btowc/3.md) function, and the resulting wide character is written. If an **l** modifier is present, the *wint\_t* (wide character) argument is written. - **s** If no **l** modifier is present: the *const char \** argument is expected to be a pointer to an array of character type (pointer to a string) containing a multibyte character sequence beginning in the initial shift state. Characters from the array are converted to wide characters (each by a call to the [**mbrtowc**(3)](/mbrtowc/3.md) function with a conversion state starting in the initial state before the first byte). The resulting wide characters are written up to (but not including) the terminating null wide character (L'\\0'). If a precision is specified, no more wide characters than the number specified are written. Note that the precision determines the number of *wide characters* written, not the number of *bytes* or *screen positions*. The array must contain a terminating null byte ('\\0'), unless a precision is given and it is so small that the number of converted wide characters reaches it before the end of the array is reached. If an **l** modifier is present: the *const wchar\_t \** argument is expected to be a pointer to an array of wide characters. Wide characters from the array are written up to (but not including) a terminating null wide character. If a precision is specified, no more than the number specified are written. The array must contain a terminating null wide character, unless a precision is given and it is smaller than or equal to the number of wide characters in the array. ## RETURN VALUE The functions return the number of wide characters written, excluding the terminating null wide character in case of the functions **swprintf**() and **vswprintf**(). On error, -1 is returned, and *errno* is set to indicate the error. ## ERRORS See [**write**(2)](/write/2.md) and [**putwc**(3)](/putwc/3.md). In addition, the following error may occur: - **EOVERFLOW** The value to be returned is greater than **INT\_MAX**. The **fwprintf**() and **wprintf**() functions may fail additionally if: - **ENOMEM** Insufficient storage space is available. ## ATTRIBUTES For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md). | | | | | --- | --- | --- | | **Interface** | **Attribute** | **Value** | | **wprintf**(), **fwprintf**(), **swprintf**(), **vwprintf**(), **vfwprintf**(), **vswprintf**() | Thread safety | MT-Safe locale | ## STANDARDS C11, POSIX.1-2008. ## HISTORY POSIX.1-2001, C99. ## NOTES The behavior of **wprintf**() et al. depends on the **LC\_CTYPE** category of the current locale. If the *format* string contains non-ASCII wide characters, the program will work correctly only if the **LC\_CTYPE** category of the current locale at run time is the same as the **LC\_CTYPE** category of the current locale at compile time. This is because the *wchar\_t* representation is platform- and locale-dependent. (The glibc represents wide characters using their Unicode (ISO/IEC 10646) code point, but other platforms don't do this. Also, the use of C99 universal character names of the form \\unnnn does not solve this problem.) Therefore, in internationalized programs, the *format* string should consist of ASCII wide characters only, or should be constructed at run time in an internationalized way (e.g., using [**gettext**(3)](/gettext/3.md) or [**iconv**(3)](/iconv/3.md), followed by [**mbstowcs**(3)](/mbstowcs/3.md)). ## SEE ALSO [**fprintf**(3)](/fprintf/3.md), [**fputwc**(3)](/fputwc/3.md), [**fwide**(3)](/fwide/3.md), [**printf**(3)](/printf/3.md), [**snprintf**(3)](/snprintf/3.md)