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


strxfrm, strxfrm_l - string transformation


#include <string.h>

size_t strxfrm(char *restrict
s1, const char *restrict s2, size_t n);

[CX] [Option Start] size_t strxfrm_l(char *restrict s1, const char *restrict s2,
n, locale_t locale); [Option End]


For strxfrm(): [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 strxfrm() [CX] [Option Start]  and strxfrm_l() [Option End]  functions shall transform the string pointed to by s2 and place the resulting string into the array pointed to by s1. The transformation is such that if strcmp() is applied to two transformed strings, it shall return a value greater than, equal to, or less than 0, corresponding to the result of strcoll() [CX] [Option Start]  or strcoll_l(), [Option End]  respectively, applied to the same two original strings [CX] [Option Start]  with the same locale. [Option End]  No more than n bytes are placed into the resulting array pointed to by s1, including the terminating NUL character. If n is 0, s1 is permitted to be a null pointer. If copying takes place between objects that overlap, the behavior is undefined.

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

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 strxfrm() [CX] [Option Start]  or strxfrm_l(), [Option End]  then check errno.

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


Upon successful completion, strxfrm() [CX] [Option Start]  and strxfrm_l() [Option End]  shall return the length of the transformed string (not including the terminating NUL character). If the value returned is n or more, the contents of the array pointed to by s1 are unspecified.

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


These functions may fail if:

[CX] [Option Start] The string pointed to by the s2 argument contains characters outside the domain of the collating sequence. [Option End]

The following sections are informative.




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

The fact that when n is 0 s1 is permitted to be a null pointer is useful to determine the size of the s1 array prior to making the transformation.






strcmp, strcoll

XBD <string.h>


First released in Issue 3. Included for alignment with the ISO C standard.

Issue 5

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

Issue 6

Extensions beyond the ISO C standard are marked.

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

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

Issue 7

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

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0624 [283], XSH/TC1-2008/0625 [283], and XSH/TC1-2008/0626 [302] are applied.

End of informative text.


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