mbsnset.cpp

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/***
*mbsnset.c - Sets first n charcaters of string to given character (MBCS)
*
*       Copyright (c) Microsoft Corporation.  All rights reserved.
*
*Purpose:
*       Sets first n charcaters of string to given character (MBCS)
*
*******************************************************************************/
#ifndef _MBCS
    #error This file should only be compiled with _MBCS defined
#endif
 
#include <corecrt_internal_mbstring.h>
#include <locale.h>
#include <string.h>
 
 
/***
* _mbsnset - Sets first n charcaters of string to given character (MBCS)
*
*Purpose:
*       Sets the first n characters of string to the supplied
*       character value.  If the length of string is less than n,
*       the length of string is used in place of n.  Handles
*       MBCS chars correctly.
*
*       There are several factors that make this routine complicated:
*               (1) The fill value may be 1 or 2 bytes long.
*               (2) The fill operation may end by hitting the count value
*               or by hitting the end of the string.
*               (3) A null terminating char is NOT placed at the end of
*               the string.
*
*       Cases to be careful of (both of these can occur at once):
*               (1) Leaving an "orphaned" trail byte in the string (e.g.,
*               overwriting a lead byte but not the corresponding trail byte).
*               (2) Writing only the 1st byte of a 2-byte fill value because the
*               end of string was encountered.
*
*Entry:
*       unsigned char *string = string to modify
*       unsigned int val = value to fill string with
*       size_t count = count of characters to fill
*
*
*Exit:
*       Returns string = now filled with char val
*
*Uses:
*
*Exceptions:
*       Input parameters are validated. Refer to the validation section of the function.
*
*******************************************************************************/
 
extern "C" unsigned char * __cdecl _mbsnset_l(
        unsigned char *string,
        unsigned int val,
        size_t count,
        _locale_t plocinfo
        )
{
        unsigned char  *start = string;
        unsigned int leadbyte = 0;
        unsigned char highval, lowval;
        _LocaleUpdate _loc_update(plocinfo);
 
        /* validation section */
        _VALIDATE_RETURN(string != nullptr || count == 0, EINVAL, nullptr);
 
        /*
         * leadbyte flag indicates if the last byte we overwrote was
         * a lead byte or not.
         */
_BEGIN_SECURE_CRT_DEPRECATION_DISABLE
        if (_loc_update.GetLocaleT()->mbcinfo->ismbcodepage == 0)
            return (unsigned char *)_strnset((char *)string, val, count);
_END_SECURE_CRT_DEPRECATION_DISABLE
 
        highval = static_cast<unsigned char>(val >> 8);
        if (highval != 0)
        {
 
            /* double byte value */
 
            lowval = (unsigned char)(val & 0x00ff);
 
            if(lowval=='\0')
            {
                _ASSERTE(("invalid MBCS pair passed to mbsnset",0));
 
                /* Ideally we would return nullptr here and signal an error
                    condition. But since this function has no other
                    error modes, there would be a good chance of crashing
                    the caller. So instead we fill the string with spaces
                    to ensure that no information leaks through
                    unexpectedly. Anyway, we do set errno to EINVAL.
                */
                errno = EINVAL;
                lowval=highval=' ';
            }
 
            while (count-- && *string) {
                leadbyte = _ismbbtruelead_l(leadbyte, *string, _loc_update.GetLocaleT());
                *string++ = highval;
 
                if (*string) {
                    leadbyte = _ismbbtruelead_l(leadbyte, *string, _loc_update.GetLocaleT());
                    *string++ = lowval;
                }
                else
                    /* overwrite orphaned highval byte */
                    *(string-1) = ' ';
            }
        }
 
        else {
            /* single byte value */
 
            while (count-- && *string) {
                leadbyte = _ismbbtruelead_l(leadbyte, *string, _loc_update.GetLocaleT());
                *string++ = (unsigned char)val;
            }
        }
 
        /* overwrite orphaned trailing byte, if necessary */
        if(leadbyte && *string)
            *string = ' ';
 
        return( start );
}
 
unsigned char * (__cdecl _mbsnset)(
        unsigned char *string,
        unsigned int val,
        size_t count
        )
{
_BEGIN_SECURE_CRT_DEPRECATION_DISABLE
    return _mbsnset_l(string, val, count, nullptr);
_END_SECURE_CRT_DEPRECATION_DISABLE
}