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# std::setlocale

From cppreference.com
< cpp‎ | locale

Defined in header `<clocale>` |  |
char* setlocale( int category, const char* locale); |  |

The `setlocale` function installs the specified system locale or its portion as the new C locale. The modifications remain in effect and influences the execution of all locale-sensitive C library functions until the next call to `setlocale`. If `locale` is a null pointer, `setlocale` queries the current C locale without modifying it.

### [edit] Parameters

category | - | locale category identifier, one of the LC_xxx macros. May be 0.
locale | - | system-specific locale identifier. Can be "" for the user-preferred locale or "C" for the minimal locale

### [edit] Return value

Pointer to a narrow null-terminated string identifying the C locale after applying the changes, if any, or null pointer on failure.

### [edit] Notes

During program startup, the equivalent of std::setlocale(LC_ALL, "C"); is executed before any user code is run.

Although the return type is char*, modifying the pointed-to characters is undefined behavior.

Because `setlocale` modifies global state which affects execution of locale-dependent functions, it is undefined behavior to call it from one thread, while another thread is executing any of the following functions: std::fprintf, std::isprint, std::iswdigit, std::localeconv, std::tolower, std::fscanf, std::ispunct, std::iswgraph, std::mblen, std::toupper, std::isalnum, std::isspace, std::iswlower, std::mbstowcs, std::towlower, std::isalpha, std::isupper, std::iswprint, std::mbtowc, std::towupper, std::isblank, std::iswalnum, std::iswpunct, std::setlocale, std::wcscoll, std::iscntrl, std::iswalpha, std::iswspace, std::strcoll, std::wcstod, std::isdigit, std::iswblank, std::iswupper, std::strerror, std::wcstombs, std::isgraph, std::iswcntrl, std::iswxdigit, std::strtod, std::wcsxfrm, std::islower, std::iswctype, std::isxdigit.

### [edit] Example

Run this code

    #include <cstdio>
    #include <clocale>
    #include <ctime>
    #include <cwchar>

    int main()
    {
        // the C locale will be UTF-8 enabled English;
        // decimal dot will be German
        // date and time formatting will be Japanese
        std::setlocale(LC_ALL, "en_US.UTF-8");
        std::setlocale(LC_NUMERIC, "de_DE");
        std::setlocale(LC_TIME, "ja_JP");

        wchar_t str[100];
        std::time_t t = std::time(NULL);
        std::wcsftime(str, 100, L"%A %c", std::localtime(&t));
        std::wprintf(L"Number: %.2f\nDate: %Ls\n", 3.14, str);
    }

Output:

    Number: 3,14
    Date: 月曜日 2011年12月19日 18時04分40秒

### [edit] See also

LC_ALLLC_COLLATELC_CTYPELC_MONETARYLC_NUMERICLC_TIME | locale categories for std::setlocale (macro constant) [edit]
locale | set of polymorphic facets that encapsulate cultural differences (class) [edit]
C documentation for setlocale

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