Support for Unicode

Unicode is a specification for supporting all character sets, including ones that can't be represented in a single byte. If you're programming for an international market, we recommend you use either Unicode or a multibyte character set (MBCS). Or, code your program so you can build it for either by changing a switch.

A wide character is a 2-byte multilingual character code. Tens of thousands of characters, comprising almost all characters used in modern computing worldwide, including technical symbols and special publishing characters, can be represented according to the Unicode specification as a single wide character encoded by using UTF-16. Characters that cannot be represented in just one wide character can be represented in a Unicode pair by using the Unicode surrogate pair feature. Because almost every character in common use is represented in UTF-16 in a single 16-bit wide character, using wide characters simplifies programming with international character sets. Wide characters encoded using UTF-16LE (for little-endian) are the native character format for Windows.

A wide-character string is represented as a wchar_t[] array and is pointed to by a wchar_t* pointer. Any ASCII character can be represented as a wide character by prefixing the letter L to the character. For example, L'\0' is the terminating wide (16-bit) NULL character. Similarly, any ASCII string literal can be represented as a wide-character string literal by prefixing the letter L to the ASCII literal (L"Hello").

Generally, wide characters take more space in memory than multibyte characters but are faster to process. In addition, only one locale can be represented at a time in a multibyte encoding, whereas all character sets in the world are represented simultaneously by the Unicode representation.

The MFC framework is Unicode-enabled throughout, and MFC accomplishes Unicode enabling by using portable macros, as shown in the following table.

Portable Data Types in MFC

Non-portable data type Replaced by this macro
char, wchar_t _TCHAR
char*, LPSTR (Win32 data type), LPWSTR LPTSTR
const char*, LPCSTR (Win32 data type), LPCWSTR LPCTSTR

Class CString uses _TCHAR as its base and provides constructors and operators for easy conversions. Most string operations for Unicode can be written by using the same logic used for handling the Windows ANSI character set, except that the basic unit of operation is a 16-bit character instead of an 8-bit byte. Unlike working with multibyte character sets, you do not have to (and should not) treat a Unicode character as if it were two distinct bytes. You do, however, have to deal with the possibility of a single character represented by a surrogate pair of wide characters. In general, do not write code that assumes the length of a string is the same as the number of characters, whether narrow or wide, that it contains.

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See also

Text and Strings
Support for Using wmain