setlocale (3p) - Linux Manuals

setlocale: set program locale


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


setlocale - set program locale


#include <locale.h>

char *setlocale(int category, const char *locale);


The setlocale() function selects the appropriate piece of the program's locale, as specified by the category and locale arguments, and may be used to change or query the program's entire locale or portions thereof. The value LC_ALL for category names the program's entire locale; other values for category name only a part of the program's locale:

Affects the behavior of regular expressions and the collation functions.
Affects the behavior of regular expressions, character classification, character conversion functions, and wide-character functions.
Affects what strings are expected by commands and utilities as affirmative or negative responses.

It also affects what strings are given by commands and utilities as affirmative or negative responses, and the content of messages.

Affects the behavior of functions that handle monetary values.
Affects the behavior of functions that handle numeric values.
Affects the behavior of the time conversion functions.

The locale argument is a pointer to a character string containing the required setting of category. The contents of this string are implementation-defined. In addition, the following preset values of locale are defined for all settings of category:

Specifies the minimal environment for C-language translation called the POSIX locale. If setlocale() is not invoked, the POSIX locale is the default at entry to main().
Equivalent to "POSIX" .
Specifies an implementation-defined native environment. This corresponds to the value of the associated environment variables, LC_* and LANG ; see the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 7, Locale and the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 8, Environment Variables.
A null pointer
Used to direct setlocale() to query the current internationalized environment and return the name of the locale.

The locale state is common to all threads within a process.


Upon successful completion, setlocale() shall return the string associated with the specified category for the new locale. Otherwise, setlocale() shall return a null pointer and the program's locale is not changed.

A null pointer for locale causes setlocale() to return a pointer to the string associated with the category for the program's current locale. The program's locale shall not be changed.

The string returned by setlocale() is such that a subsequent call with that string and its associated category shall restore that part of the program's locale. The application shall not modify the string returned which may be overwritten by a subsequent call to setlocale().


No errors are defined.

The following sections are informative.




The following code illustrates how a program can initialize the international environment for one language, while selectively modifying the program's locale such that regular expressions and string operations can be applied to text recorded in a different language:

setlocale(LC_ALL, "De");
setlocale(LC_COLLATE, "Fr [at] dict");

Internationalized programs must call setlocale() to initiate a specific language operation. This can be done by calling setlocale() as follows:

setlocale(LC_ALL, "");

Changing the setting of LC_MESSAGES has no effect on catalogs that have already been opened by calls to catopen().


The ISO C standard defines a collection of functions to support internationalization. One of the most significant aspects of these functions is a facility to set and query the international environment. The international environment is a repository of information that affects the behavior of certain functionality, namely:

Character handling


Date/time formatting

Numeric editing

Monetary formatting


The setlocale() function provides the application developer with the ability to set all or portions, called categories, of the international environment. These categories correspond to the areas of functionality mentioned above. The syntax for setlocale() is as follows:

char *setlocale(int category, const char *locale);

where category is the name of one of following categories, namely:







In addition, a special value called LC_ALL directs setlocale() to set all categories.

There are two primary uses of setlocale():

Querying the international environment to find out what it is set to

Setting the international environment, or locale, to a specific value

The behavior of setlocale() in these two areas is described below. Since it is difficult to describe the behavior in words, examples are used to illustrate the behavior of specific uses.

To query the international environment, setlocale() is invoked with a specific category and the NULL pointer as the locale. The NULL pointer is a special directive to setlocale() that tells it to query rather than set the international environment. The following syntax is used to query the name of the international environment:

    LC_NUMERIC, LC_TIME},(char *) NULL);

The setlocale() function shall return the string corresponding to the current international environment. This value may be used by a subsequent call to setlocale() to reset the international environment to this value. However, it should be noted that the return value from setlocale() may be a pointer to a static area within the function and is not guaranteed to remain unchanged (that is, it may be modified by a subsequent call to setlocale()). Therefore, if the purpose of calling setlocale() is to save the value of the current international environment so it can be changed and reset later, the return value should be copied to an array of char in the calling program.

There are three ways to set the international environment with setlocale():


This usage sets a specific category in the international environment to a specific value corresponding to the value of the string. A specific example is provided below:

setlocale(LC_ALL, "fr_FR.ISO-8859-1");

In this example, all categories of the international environment are set to the locale corresponding to the string "fr_FR.ISO-8859-1", or to the French language as spoken in France using the ISO/IEC 8859-1:1998 standard codeset.

If the string does not correspond to a valid locale, setlocale() shall return a NULL pointer and the international environment is not changed. Otherwise, setlocale() shall return the name of the locale just set.


The ISO C standard states that one locale must exist on all conforming implementations. The name of the locale is C and corresponds to a minimal international environment needed to support the C programming language.


This sets a specific category to an implementation-defined default. This corresponds to the value of the environment variables.




Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at .


exec(), isalnum(), isalpha(), isblank(), iscntrl(), isdigit(), isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(), iswalnum(), iswalpha(), iswblank(), iswcntrl(), iswctype(), iswdigit(), iswgraph(), iswlower(), iswprint(), iswpunct(), iswspace(), iswupper(), iswxdigit(), isxdigit(), localeconv(), mblen(), mbstowcs(), mbtowc(), nl_langinfo(), printf(), scanf(), setlocale, strcoll(), strerror(), strfmon() , strtod(), strxfrm(), tolower(), toupper(), towlower(), towupper(), wcscoll(), wcstod(), wcstombs(), wcsxfrm(), wctomb(), the Base Definitions volume of IEEE Std 1003.1-2001, <langinfo.h>, <locale.h>