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man pages section 3: Basic Library Functions

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Updated: July 2017



strxfrm - string transformation


#include <string.h>

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


The strxfrm() function transforms the string pointed to by s2 and places the resulting string into the array pointed to by s1. The transformation is such that if strcmp(3C) is applied to two transformed strings, it returns a value greater than, equal to or less than 0, corresponding to the result of strcoll(3C) 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.

The strxfrm() function does 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.

Return Values

Upon successful completion, strxfrm() returns 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 indeterminate.

On error, strxfrm() may set errno but no return value is reserved to indicate the error.


The transformation function is such that two transformed strings can be ordered by strcmp(3C) 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.


Example 1 A sample of using the strxfm() function.

The value of the following expression is the size of the array needed to hold the transformation of the string pointed to by s.

1 + strxfrm(NULL, s, 0);



LC_COLLATE database for locale


See attributes(5) for descriptions of the following attributes:

Interface Stability
MT-Safe with exceptions

The strxfrm() function can be used safely in a multithreaded application, as long as setlocale(3C) is not being called to change the locale.

See Also

localedef(1), setlocale(3C), strcmp(3C), strcoll(3C), wscoll(3C), attributes(5), environ(5), standards(5)