The Open Group Base Specifications Issue 7, 2018 edition
IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008)
Copyright © 2001-2018 IEEE and The Open Group


wcsxfrm, wcsxfrm_l - wide-character string transformation


#include <wchar.h>

size_t wcsxfrm(wchar_t *restrict
ws1, const wchar_t *restrict ws2,

[CX] [Option Start] size_t wcsxfrm_l(wchar_t *restrict ws1, const wchar_t *restrict ws2,
n, locale_t locale); [Option End]


For wcsxfrm(): [CX] [Option Start]  The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard. [Option End]

The wcsxfrm() [CX] [Option Start]  and wcsxfrm_l() [Option End]  functions shall transform the wide-character string pointed to by ws2 and place the resulting wide-character string into the array pointed to by ws1. The transformation shall be such that if wcscmp() is applied to two transformed wide strings, it shall return a value greater than, equal to, or less than 0, corresponding to the result of wcscoll() [CX] [Option Start]  and wcscoll_l() [Option End]  applied to the same two original wide-character strings, and the same LC_COLLATE category of the current locale [CX] [Option Start]  or the locale object locale, [Option End]  respectively. No more than n wide-character codes shall be placed into the resulting array pointed to by ws1, including the terminating null wide-character code. If n is 0, ws1 is permitted to be a null pointer. If copying takes place between objects that overlap, the behavior is undefined.

[CX] [Option Start] The wcsxfrm() and wcsxfrm_l() functions shall not change the setting of errno if successful.

Since no return value is reserved to indicate an error, an application wishing to check for error situations should set errno to 0, then call wcsxfrm() or wcsxfrm_l(), then check errno.

The behavior is undefined if the locale argument to wcsxfrm_l() is the special locale object LC_GLOBAL_LOCALE or is not a valid locale object handle. [Option End]


The wcsxfrm() [CX] [Option Start]  and wcsxfrm_l() [Option End]  functions shall return the length of the transformed wide-character string (not including the terminating null wide-character code). If the value returned is n or more, the contents of the array pointed to by ws1 are unspecified.

[CX] [Option Start] On error, the wcsxfrm() and wcsxfrm_l() functions may set errno, but no return value is reserved to indicate an error. [Option End]


These functions may fail if:

[CX] [Option Start] The wide-character string pointed to by ws2 contains wide-character codes outside the domain of the collating sequence. [Option End]

The following sections are informative.




The transformation function is such that two transformed wide-character strings can be ordered by wcscmp() as appropriate to collating sequence information in the current locale (category LC_COLLATE).

The fact that when n is 0 ws1 is permitted to be a null pointer is useful to determine the size of the ws1 array prior to making the transformation.






wcscmp, wcscoll

XBD <wchar.h>


First released in Issue 4. Derived from the MSE working draft.

Issue 5

Moved from ENHANCED I18N to BASE and the [ENOSYS] error is removed.

The DESCRIPTION is updated to indicate that errno is not changed if the function is successful.

Issue 6

In earlier versions, this function was required to return -1 on error.

Extensions beyond the ISO C standard are marked.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

The wcsxfrm() prototype is updated for alignment with the ISO/IEC 9899:1999 standard.

Issue 7

The wcsxfrm_l() function is added from The Open Group Technical Standard, 2006, Extended API Set Part 4.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0728 [302], XSH/TC1-2008/0729 [283], XSH/TC1-2008/0730 [283], and XSH/TC1-2008/0731 [302] are applied.

End of informative text.


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