wctomb.cpp

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//
// wctomb.cpp
//
//      Copyright (c) Microsoft Corporation. All rights reserved.
//
// Functions to convert a wide character to the equivalent multibyte character,
// according to the LC_CTYPE category of the current locale.  The return value
// (or *return_value, for the _s-suffixed functions) depends on the destination
// and destination_count:
//  * If destination == nullptr && count == 0, number of bytes needed for conversion
//  * If destination != nullptr:  the number of bytes used for the conversion
//  * If destination == nullptr && count >  0, the state information
//    (0 for no state dependency, 1 if a state dependent encoding)
//
// Historically Windows has not supported state-dependent encodings for wctomb,
// however UTF-8 can possible require more than one input wchar_t and maintain
// state between calls.
//
// The return_value pointer may be null.
//
#include <corecrt_internal.h>
#include <corecrt_internal_mbstring.h>
#include <corecrt_internal_ptd_propagation.h>
#include <errno.h>
#include <limits.h>
#include <locale.h>
#include <stdlib.h>
 
 
extern "C" int __cdecl _wctomb_internal(
    int*               const return_value,
    char*              const destination,
    size_t             const destination_count,
    wchar_t            const wchar,
    __crt_cached_ptd_host&   ptd
    )
{
    // Did the caller request if this is a state dependent encoding?
    if (!destination && destination_count > 0)
    {
        // Indicate do not have state-dependent encodings:
        if (return_value != nullptr)
            *return_value = 0;
 
        return 0;
    }
 
    if (return_value)
        *return_value = -1;
 
    // We need to cast destination_count to int, so we make sure we are not
    // going to truncate destination_count:
    _UCRT_VALIDATE_RETURN_ERRCODE(ptd, destination_count <= INT_MAX, EINVAL);
    _locale_t const locale = ptd.get_locale();
 
    if (locale->locinfo->_public._locale_lc_codepage == CP_UTF8)
    {
        // Unlike c16rtomb. wctomb/wcrtomb have no ability to process a partial code point.
        // So, we could call c16rtomb and check for a lone surrogate or other error, or for simplicity
        // We can instead just call c32rtomb and check for any error. I choose the latter.
        mbstate_t state{};
        int result = static_cast<int>(__crt_mbstring::__c32rtomb_utf8(destination, static_cast<char32_t>(wchar), &state, ptd));
        if (return_value != nullptr)
        {
            *return_value = result;
        }
        if (result <= 4)
        {
            return 0;
        }
        else
        {
            return ptd.get_errno().value_or(0);
        }
    }
 
    // Check for C-locale behavior, which merely casts it to char (if in range)
    // for ASCII-ish behavior.
    if (!locale->locinfo->locale_name[LC_CTYPE])
    {
        // See if the WCHAR is > ASCII-ish range
        if (wchar > 255)  // Validate high byte
        {
            // Too big, can't convert, clear buffer and return error
            if (destination != nullptr && destination_count > 0)
            {
                memset(destination, 0, destination_count);
            }
 
            return ptd.get_errno().set(EILSEQ);
        }
 
        // ASCII-ish, just cast to a (char)
        if (destination != nullptr)
        {
            _UCRT_VALIDATE_RETURN_ERRCODE(ptd, destination_count > 0, ERANGE);
            *destination = static_cast<char>(wchar);
        }
 
        if (return_value != nullptr)
        {
            // casting one WCHAR emits a single char
            *return_value = 1;
        }
 
        // We're done
        return 0;
    }
    else
    {
        BOOL default_used{};
        int const size = __acrt_WideCharToMultiByte(
            locale->locinfo->_public._locale_lc_codepage,
            0,
            &wchar,
            1,
            destination,
            static_cast<int>(destination_count),
            nullptr,
            &default_used);
 
        if (size == 0 || default_used)
        {
            if (size == 0 && GetLastError() == ERROR_INSUFFICIENT_BUFFER)
            {
                if (destination && destination_count > 0)
                {
                    memset(destination, 0, destination_count);
                }
 
                _UCRT_VALIDATE_RETURN_ERRCODE(ptd, ("Buffer too small", 0), ERANGE);
            }
 
            return ptd.get_errno().set(EILSEQ);
        }
 
        if (return_value)
        {
            *return_value = size;
        }
 
        return 0;
    }
 
    // The last thing was an if/else, so we already returned.
}
 
extern "C" int __cdecl _wctomb_s_l(
    int*      const return_value,
    char*     const destination,
    size_t    const destination_count,
    wchar_t   const wchar,
    _locale_t const locale
    )
{
    __crt_cached_ptd_host ptd(locale);
    return _wctomb_internal(return_value, destination, destination_count, wchar, ptd);
}
 
extern "C" errno_t __cdecl wctomb_s (
    int*    const return_value,
    char*   const destination,
    size_t  const destination_count,
    wchar_t const wchar
    )
{
    __crt_cached_ptd_host ptd;
    return _wctomb_internal(return_value, destination, destination_count, wchar, ptd);
}
 
extern "C" int __cdecl _wctomb_l(
    char*     const destination,
    wchar_t   const wchar,
    _locale_t const locale
    )
{
    __crt_cached_ptd_host ptd(locale);
 
    int return_value{};
    errno_t const e = _wctomb_internal(
        &return_value,
        destination,
        ptd.get_locale()->locinfo->_public._locale_mb_cur_max,
        wchar,
        ptd);
 
    if (e != 0)
    {
        return -1;
    }
 
    return return_value;
}
 
// Disable the OACR error that warns that 'MB_CUR_MAX' doesn't properly constrain buffer 'destination'.
// wctomb() doesn't take a buffer size, so the function's contract is inherently dangerous.
__pragma(warning(push))
__pragma(warning(disable:__WARNING_POTENTIAL_BUFFER_OVERFLOW_HIGH_PRIORITY)) // 26015
 
extern "C" int __cdecl wctomb(
    char*   const destination,
    wchar_t const wchar
    )
{
    __crt_cached_ptd_host ptd;
 
    int return_value{};
    errno_t const e = _wctomb_internal(&return_value, destination, MB_CUR_MAX, wchar, ptd);
    if (e != 0)
    {
        return -1;
    }
 
    return return_value;
}
 
__pragma(warning(pop))