WideCharToMultiByte info  Overview  Group

The WideCharToMultiByte function maps a wide-character string to a new character string. The new character string is not necessarily from a multibyte character set.

int WideCharToMultiByte(

UINT CodePage,	// code page
DWORD dwFlags,	// performance and mapping flags
LPCWSTR lpWideCharStr,	// address of wide-character string
int cchWideChar,	// number of characters in string
LPSTR lpMultiByteStr,	// address of buffer for new string
int cchMultiByte,	// size of buffer
LPCSTR lpDefaultChar,	// address of default for unmappable characters
LPBOOL lpUsedDefaultChar	// address of flag set when default char. used
);

Parameters

CodePage

Specifies the code page used to perform the conversion. This parameter can be given the value of any code page that is installed or available in the system. You can also specify one of the following values:

Value	Meaning
CP_ACP	ANSI code page
CP_MACCP	Macintosh code page
CP_OEMCP	OEM code page
CP_UTF7	Translate using UTF-7
CP_UTF8	Translate using UTF-8

dwFlags

A set of bit flags that specify the handling of unmapped characters. The function performs more quickly when none of these flags is set. The following flag constants are defined:

Value	Meaning
WC_NO_BEST_FIT_CHARS	Any Unicode characters that do not translate directly to multibyte equivalents will be translated to the default character (see lpDefaultChar parameter). In other words, if translating from Unicode to multibyte and back to Unicode again does not yield the exact same Unicode character, the default character is used. This flag may be used by itself or in combination with the other dwFlag options.
WC_COMPOSITECHECK	Convert composite characters to precomposed characters.
WC_DISCARDNS	Discard nonspacing characters during conversion.
WC_SEPCHARS	Generate separate characters during conversion. This is the default conversion behavior.
WC_DEFAULTCHAR	Replace exceptions with the default character during conversion.

When WC_COMPOSITECHECK is specified, the function converts composite characters to precomposed characters. A composite character consists of a base character and a nonspacing character, each having different character values. A precomposed character has a single character value for a base/nonspacing character combination. In the character è, the e is the base character, and the accent grave mark is the nonspacing character.

When an application specifies WC_COMPOSITECHECK, it can use the last 3 flags in this list (WC_DISCARDNS, WC_SEPCHARS, and WC_DEFAULTCHAR) to customize the conversion to precomposed characters. These flags determine the function’s behavior when there is no precomposed mapping for a base/nonspace character combination in a wide-character string. These last 3 flags can only be used if the WC_COMPOSITECHECK flag is set.

The function’s default behavior is to generate separate characters (WC_SEPCHARS) for unmapped composite characters.

lpWideCharStr

Points to the wide-character string to be converted.

cchWideChar

Specifies the number of characters in the string pointed to by the lpWideCharStr parameter. If this value is -1, the string is assumed to be null-terminated and the length is calculated automatically.

lpMultiByteStr

Points to the buffer to receive the translated string.

cchMultiByte

Specifies the size in characters of the buffer pointed to by the lpMultiByteStr parameter. If this value is zero, the function returns the number of bytes required for the buffer. (In this case, the lpMultiByteStr buffer is not used.)

lpDefaultChar

Points to the character used if a wide character cannot be represented in the specified code page. If this parameter is NULL, a system default value is used. The function is faster when both lpDefaultChar and lpUsedDefaultChar are NULL.

lpUsedDefaultChar

Points to a flag that indicates whether a default character was used. The flag is set to TRUE if one or more wide characters in the source string cannot be represented in the specified code page. Otherwise, the flag is set to FALSE. This parameter may be NULL. The function is faster when both lpDefaultChar and lpUsedDefaultChar are NULL.

Return Values

If the function succeeds, and cchMultiByte is nonzero, the return value is the number of bytes written to the buffer pointed to by lpMultiByteStr.

If the function succeeds, and cchMultiByte is zero, the return value is the required size, in bytes, for a buffer that can receive the translated string.

If the function fails, the return value is zero. To get extended error information, call GetLastError. GetLastError may return one of the following error codes:

ERROR_INSUFFICIENT_BUFFER
ERROR_INVALID_FLAGS
ERROR_INVALID_PARAMETER

Remarks

The lpMultiByteStr and lpWideCharStr pointers must not be the same. If they are the same, the function fails, and GetLastError returns ERROR_INVALID_PARAMETER.

An application can use the lpDefaultChar parameter to change the default character used for the conversion.

As noted earlier, the WideCharToMultiByte function operates most efficiently when both lpDefaultChar and lpUsedDefaultChar are NULL. The following table shows the behavior of WideCharToMultiByte for the four combinations of lpDefaultChar and lpUsedDefaultChar :

lpDefaultChar	lpUsedDefaultChar	Result
NULL	NULL	No default checking. This is the most efficient, quick way to use this function.
non-NULL	NULL	Uses the specified default character, but does not set lpUsedDefaultChar.
NULL	non-NULL	Uses the system default character and sets lpUsedDefaultChar if necessary.
non-NULL	non-NULL	Uses the specified default character and sets lpUsedDefaultChar if necessary.

See Also

MultiByteToWideChar 

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