Multibyte Functions in Microsoft C Run-time

Multibyte functions is useful in Far East countries, such as China (including Taiwan and Hong Kong), Korea, and Japan. The code pages of these countries are generally compliant with ASCII when the character codes are less than 0x80, and the meaning of the codes (and perhaps the code immediately follows) vary when they are greater than 0x80. For example, the name of the current Chinese Premiere, Mr Zhu Rongji, is encoded in Codepage 936 (GBK) as 0xD6EC 0xE946 0xBBF9. Please note that the second character Rong is encoded as 0xE946, the second byte being lower than 0x80 (However, the most common characters in CP 936 have both bytes greater than 0x80).

To use multibyte functions, the first step is to set the code page. Of course, if you are using the OS default code page, this step could be omitted. You should use the _setmbcp function.

int _setmbcp(int codepage);

Sets a new multibyte code page.

• _MB_CP_SBCS   = 0   Use single-byte code page
• _MB_CP_OEM    = -2  Use OEM code page obtained from operating system at program startup
• _MB_CP_ANSI   = -3  Use ANSI code page obtained from operating system at program startup
• _MB_CP_LOCALE = -4  Use the current locale's code page obtained from a previous call to setlocale

#include <locale.h>
#include <mbctype.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
    setlocale(LC_ALL, "Chinese_Taiwan");
    _setmbcp(_MB_CP_LOCALE);
    printf("%d\n", _getmbcp());
    return 0;
}

int _getmbcp(void);

Returns the current multibyte code page.

• _ismbbkalnum tests with _MS
• _ismbbkprint tests with (_MS|_MP)
• _ismbbkpunct tests with _MP
• _ismbbkana tests with (_MS|_MP) (CP 932 only)
• _ismbblead tests with _M1
• _ismbbtrail tests with _M2

Of these routines I only want to explain ismbblead and ismbbtrail. The former tests whether an integer is the first byte of a multibyte character, and the latter tests whether an integer is the second byte of a multibyte character. The functions _ismbslead and _ismbstrail (they have no inline versions) are also interesting that they test whether a given character in a string is lead byte or trail byte depending on context. For example,

#include <mbctype.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
    char s[] = "\326\354";  /* ZHU1 */
    _setmbcp(936);          /* Chinese GBK */
    printf("%d\n", _ismbblead(s[1]));
    printf("%d\n", _ismbslead(s, &s[1]));
    return 0;
}

More interesting multibyte string functions are defined in mbstring.h. They include equivalents to standard string routines (taking into account the properties of multibyte characters), character type routines, and conversion routines. We shall name one from each category for explanation.

size_t _mbslen(const unsigned char *string);

Returns the number of multibyte characters in string.

#include <mbctype.h>
#include <mbstring.h>
#include <stdio.h>
#include <string.h>

int main(int argc, char *argv[])
{
    char s[] = "\326\354";  /* ZHU1 */
    _setmbcp(936);          /* Chinese GBK */
    printf("%d\n", strlen(s));
    printf("%d\n", _mbslen(s));
    return 0;
}

int _mbbtype(unsigned char c, int type);

Returns the type of a byte.

• _MBC_SINGLE  = 0  denotes valid single byte char
• _MBC_LEAD    = 1  denotes lead byte
• _MBC_TRAIL   = 2  denotes trailing byte
• _MBC_ILLEGAL = (-1) denotes illegal byte

size_t mbstowcs(wchar_t *wcstr, const char *mbstr, size_t count);

Converts a sequence of multibyte characters to a corresponding sequence of wide characters.

/* mbstowcs.c - Demonstration of the mbstowcs function */

#include <stdio.h>
#include <stdlib.h>
#include <locale.h>

int main()
{
    wchar_t wcstr[64];
    char    mbstr[] = "ABC - A Unicode conversion test";
    size_t  n, i;

    // Set locale to the codepage of Simplified Chinese
    //
    // NB: mbstowcs is affected by locale information. By the way, the
    // MBSTOWCS example given in MSDN makes no sense at all.
    //
    setlocale(LC_ALL, "English");

    // Convert the string
    n = mbstowcs(wcstr, mbstr, _mbstrlen(mbstr));

    // Output the Unicode string to the screen
    for( i = 0; i < n; i++ )
        printf( "%.4X\t", wcstr[i] );

    return 0;
}

0041    0042    0043    0020    002D    0020    0041    0020    0055    006E
0069    0063    006F    0064    0065    0020    0063    006F    006E    0076
0065    0072    0073    0069    006F    006E    0020    0074    0065    0073
0074

OK. I am a little tired now. Enough for today.

2001-12-16, written by Wu Yongwei