strxfrm - string transformation based on LC_COLLATE

Syntax	#include <string.h> size_t strxfrm(char *s1, const char *s2, size_t n);
Description	strxfrm() transforms the string s2 and places the resulting string into the array s1. The transformation is such that if strcmp() were applied to two transformed strings, it would return a value corresponding to the result of strcoll() applied to the same two original strings. The transformation is based on the collating sequence defined by the local setting of the program ́s LC_COLLATE category (see setlocale()). A maximum of 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.
Return val.	Length of the transformed string (excluding the terminating null byte)
		if successful.
Return val.	Value ≥ n	The contents of the array s1 are indeterminate.
	Since no return value is reserved to indicate an error, errors can only be detected as follows: by setting errno to 0, calling the strxfrm() function, and then checking errno after the function returns. If errno is non-zero, it may be assumed that an error occurred.
Errors	strxfrm() will fail if:
	EINVAL	The s2 argument contains characters outside the domain of the collating sequence.
Notes	A string terminated with the null byte (\0) is expected as argument s2. String s2 is not modified by strxfrm(). The transformation is performed in a work area. If the return value is greater than or equal to n, the contents of string s1 will be indeterminate, since no null byte was written. If the hexadecimal value 0 has been assigned to one of the characters in string s2 in the current locale, the transformed string will be terminated using that character as the null byte.
See also	setlocale(), strcoll(), strcmp(), string.h.