IsTextUnicode

The IsTextUnicode function determines whether a buffer is likely to contain a form of Unicode text. The function uses various statistical and deterministic methods to make its determination, under the control of flags passed via lpi. When the function returns, the results of such tests are reported via lpi.

DWORD IsTextUnicode(
  CONST LPVOID lpBuffer, // input buffer to be examined
  int cb,                // size of input buffer
  LPINT lpi              // options
);

Parameters

lpBuffer

[in] Pointer to the input buffer to be examined.

cb

[in] Specifies the size, in bytes, of the input buffer pointed to by lpBuffer.

lpi

[in/out] On input, specifies the tests to be applied to the input buffer text. On output, receives the results of the specified tests: 1 if the contents of the buffer pass a test, zero for failure. Only flags that are set upon input to the function are significant upon output.

If lpi is NULL, the function uses all available tests to determine whether the data in the buffer is likely to be Unicode text.

The following table shows the constants used with *lpi's bit flags.

Value	Meaning
IS_TEXT_UNICODE_ASCII16	The text is Unicode, and contains onlyzero-extended ASCII values/characters.
IS_TEXT_UNICODE_REVERSE_ASCII16	Same as the preceding, except that the Unicode text is byte-reversed.
IS_TEXT_UNICODE_STATISTICS	The text is probably Unicode, with the determination made by applying statistical analysis. Absolute certainty is not guaranteed. See the following Remarks section.
IS_TEXT_UNICODE_REVERSE_STATISTICS	Same as the preceding, except that the probably-Unicode text is byte-reversed.
IS_TEXT_UNICODE_CONTROLS	The text contains Unicode representations of one or more of these nonprinting characters: RETURN, LINEFEED, SPACE, CJK_SPACE, TAB.
IS_TEXT_UNICODE_REVERSE_CONTROLS	Same as the preceding, except that the Unicode characters are byte-reversed.
IS_TEXT_UNICODE_BUFFER_TOO_SMALL	There are too few characters in the buffer for meaningful analysis (fewer than two bytes).
IS_TEXT_UNICODE_SIGNATURE	The text contains the Unicode byte-order mark (BOM) 0xFEFF as its first character.
IS_TEXT_UNICODE_REVERSE_SIGNATURE	The text contains the Unicode byte-reversed byte-order mark (Reverse BOM) 0xFFFE as its first character.
IS_TEXT_UNICODE_ILLEGAL_CHARS	The text contains one of these Unicode-illegal characters: embedded Reverse BOM, UNICODE_NUL, CRLF (packed into one WORD), or 0xFFFF.
IS_TEXT_UNICODE_ODD_LENGTH	The number of characters in the string is odd. A string of odd length cannot (by definition) be Unicode text.
IS_TEXT_UNICODE_NULL_BYTES	The text contains null bytes, which indicate non-ASCII text.
IS_TEXT_UNICODE_UNICODE_MASK	This flag constant is a combination of IS_TEXT_UNICODE_ASCII16, IS_TEXT_UNICODE_STATISTICS, IS_TEXT_UNICODE_CONTROLS, IS_TEXT_UNICODE_SIGNATURE.
IS_TEXT_UNICODE_REVERSE_MASK	This flag constant is a combination of IS_TEXT_UNICODE_REVERSE_ASCII16, IS_TEXT_UNICODE_REVERSE_STATISTICS, IS_TEXT_UNICODE_REVERSE_CONTROLS, IS_TEXT_UNICODE_REVERSE_SIGNATURE.
IS_TEXT_UNICODE_NOT_UNICODE_MASK	This flag constant is a combination of IS_TEXT_UNICODE_ILLEGAL_CHARS, IS_TEXT_UNICODE_ODD_LENGTH, and two currently unused bit flags.
IS_TEXT_UNICODE_NOT_ASCII_MASK	This flag constant is a combination of IS_TEXT_UNICODE_NULL_BYTES and three currently unused bit flags.

Return Values

The function returns nonzero if the data in the buffer passes the specified tests.

The function returns zero if the data in the buffer does not pass the specified tests.

In either case, lpi contains the results of the specific tests the function applied to make its determination.

Remarks

As noted in the preceding table of flag constants, the IS_TEXT_UNICODE_STATISTICS and IS_TEXT_UNICODE_REVERSE_STATISTICS tests use statistical analysis. These tests are not foolproof. The statistical tests assume certain amounts of variation between low and high bytes in a string, and some ASCII strings can slip through. For example, if lpBuffer points to the ASCII string 0x41, 0x0A, 0x0D, 0x1D (A\n\r^Z), the string passes the IS_TEXT_UNICODE_STATISTICS test, though failure would be preferable.

Requirements

  Windows NT/2000: Requires Windows NT 3.5 or later.
  Windows 95/98: Unsupported.
  Header: Declared in Winbase.h; include Windows.h.
  Library: Use Advapi32.lib.

See Also

Unicode and Character Sets Overview, Unicode and Character Set Functions