---
name: "wcsxfrm"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd", "macos"]
url: "https://new.carta.tech/wcsxfrm"
---

# wcsxfrm(3)

transform a wide string under locale

## NAME

**wcsxfrm** – transform a wide string under locale

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<wchar.h\>**

*size\_t*\

**wcsxfrm**(*wchar\_t \* restrict dst*, *const wchar\_t \* restrict src*, *size\_t n*);

## DESCRIPTION

The **wcsxfrm**() function transforms a null-terminated wide character string pointed to by *src* according to the current locale collation order then copies the transformed string into *dst*. No more than *n* wide characters are copied into *dst*, including the terminating null character added. If *n* is set to 0 (it helps to determine an actual size needed for transformation), *dst* is permitted to be a NULL pointer.

Comparing two strings using **wcscmp**() after **wcsxfrm**() is equivalent to comparing two original strings with **wcscoll**().

## RETURN VALUES

Upon successful completion, **wcsxfrm**() returns the length of the transformed string not including the terminating null character. If this value is *n* or more, the contents of *dst* are indeterminate.

## SEE ALSO

[setlocale(3)](/setlocale/3.md), [strxfrm(3)](/strxfrm/3.md), [wcscmp(3)](/wcscmp/3.md), [wcscoll(3)](/wcscoll/3.md)

## STANDARDS

The **wcsxfrm**() function conforms to ISO/IEC 9899:1999 (“ISO C99”).

## BUGS

The current implementation of **wcsxfrm**() only works in single-byte LC\_CTYPE locales, and falls back to using **wcsncpy**() in locales with extended character sets.

Comparing two strings using **wcscmp**() after **wcsxfrm**() is *not* always equivalent to comparison with **wcscoll**(); **wcsxfrm**() only stores information about primary collation weights into *dst*, whereas **wcscoll**() compares characters using both primary and secondary weights.