The Open Group Base Specifications Issue 7, 2018 edition
IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008)
Copyright © 2001-2018 IEEE and The Open Group


towctrans, towctrans_l - wide-character transliteration


#include <wctype.h>

wint_t towctrans(wint_t
wc, wctrans_t desc);

[CX] [Option Start] wint_t towctrans_l(wint_t wc, wctrans_t desc,
locale); [Option End]


For towctrans(): [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 POSIX.1-2017 defers to the ISO C standard. [Option End]

The towctrans() [CX] [Option Start]  and towctrans_l() [Option End]  functions shall transliterate the wide-character code wc using the mapping described by desc.

The current setting of the LC_CTYPE category in the current locale [CX] [Option Start]  or in the locale represented by locale, [Option End]  respectively, should be the same as during the call to wctrans() [CX] [Option Start]  or wctrans_l() [Option End]  that returned the value desc.

If the value of desc is invalid (that is, not obtained by a call to wctrans() or desc is invalidated by a subsequent call to setlocale() that has affected category LC_CTYPE), the result is unspecified.

[CX] [Option Start] If the value of desc is invalid (that is, not obtained by a call to wctrans_l() with the same locale object locale) the result is unspecified. [Option End]

[CX] [Option Start] An application wishing to check for error situations should set errno to 0 before calling towctrans() or towctrans_l().

If errno is non-zero on return, an error has occurred.

The behavior is undefined if the locale argument to towctrans_l() is the special locale object LC_GLOBAL_LOCALE or is not a valid locale object handle. [Option End]


If successful, the towctrans() [CX] [Option Start]  and towctrans_l() [Option End]  functions shall return the mapped value of wc using the mapping described by desc. Otherwise, they shall return wc unchanged.


These functions may fail if:

[CX] [Option Start] desc contains an invalid transliteration descriptor. [Option End]

The following sections are informative.




The strings "tolower" and "toupper" are reserved for the standard mapping names. In the table below, the functions in the left column are equivalent to the functions in the right column.

towlower(wc)            towctrans(wc, wctrans("tolower"))
towlower_l(wc, locale)  towctrans_l(wc, wctrans("tolower"), locale)
towupper(wc)            towctrans(wc, wctrans("toupper"))
towupper_l(wc, locale)  towctrans_l(wc, wctrans("toupper"), locale)






towlower, towupper, wctrans

XBD <wctype.h>


First released in Issue 5. Derived from ISO/IEC 9899:1990/Amendment 1:1995 (E).

Issue 6

Extensions beyond the ISO C standard are marked.

Issue 7

The towctrans_l() function is added from The Open Group Technical Standard, 2006, Extended API Set Part 4.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0675 [302], XSH/TC1-2008/0676 [283], and XSH/TC1-2008/0677 [283] are applied.

End of informative text.


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