---
name: "strxfrm"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/strxfrm"
---

# strxfrm(3)

transform a string under locale

## NAME

**strxfrm**, **strxfrm\_l** – transform a string under locale

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<string.h\>**

*size\_t*\

**strxfrm**(*char \*restrict s1*, *const char \*restrict s2*, *size\_t n*);

**#include \<string.h\>**

**#include \<xlocale.h\>**

*size\_t*\

**strxfrm\_l**(*char \*restrict s1*, *const char \*restrict s2*, *size\_t n*, *locale\_t loc*);

## DESCRIPTION

The **strxfrm**() function transforms a null-terminated string pointed to by *s2* according to the current locale collation if any, then copies the transformed string into *s1*. Not more than *n* characters are copied into *s1*, including the terminating null character added. If *n* is set to 0 (it helps to determine an actual size needed for transformation), *s1* is permitted to be a NULL pointer.

Comparing two strings using **strcmp**() after **strxfrm**() is equal to comparing two original strings with **strcoll**().

Although the **strxfrm**() function uses the current locale, the **strxfrm\_l**() function may be passed a locale directly. See [xlocale(3)](/xlocale/3.md) for more information.

## RETURN VALUES

Upon successful completion, **strxfrm**() returns the length of the transformed string not including the terminating null character. If this value is *n* or more, the contents of *s1* are indeterminate.

## SEE ALSO

[setlocale(3)](/setlocale/3.md), [strcmp(3)](/strcmp/3.md), [strcoll(3)](/strcoll/3.md), [wcsxfrm(3)](/wcsxfrm/3.md), [xlocale(3)](/xlocale/3.md)

## STANDARDS

The **strxfrm**() function conforms to ISO/IEC 9899:1990 (“ISO C90”).