STRXFRM(3P) POSIX Programmer's Manual STRXFRM(3P)

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

strxfrm, strxfrm_l — string transformation

#include <string.h>
size_t strxfrm(char *restrict s1, const char *restrict s2, size_t n);
size_t strxfrm_l(char *restrict s1, const char *restrict s2,
    size_t n, locale_t locale);

For strxfrm(): 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.

The strxfrm() and strxfrm_l() 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() or strcoll_l(), respectively, applied to the same two original strings with the same locale. 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.

The strxfrm() and strxfrm_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 strxfrm() or strxfrm_l(), then check errno.

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.

Upon successful completion, strxfrm() and strxfrm_l() 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() and strxfrm_l() may set errno but no return value is reserved to indicate an error.

These functions may fail if:

The string pointed to by the s2 argument contains characters outside the domain of the collating sequence.

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()

The Base Definitions volume of POSIX.1‐2017, <string.h>

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see .

2017 IEEE/The Open Group