The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
A newer edition of this document exists here


strxfrm - string transformation


#include <string.h>

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


[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 IEEE Std 1003.1-2001 defers to the ISO C standard. [Option End]

The strxfrm() function 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() applied to the same two original strings. No more than n bytes are placed into the resulting array pointed to by s1, including the terminating null byte. 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() function 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(), then check errno. [Option End]


Upon successful completion, strxfrm() shall return the length of the transformed string (not including the terminating null byte). If the value returned is n or more, the contents of the array pointed to by s1 are unspecified.

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


The strxfrm() function 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 program's 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 IEEE Std 1003.1-2001, <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.

End of informative text.

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