The IsTextUnicode function determines whether a buffer probably contains 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. If all specified tests are passed, the function returns TRUE; otherwise, it returns FALSE.
DWORD IsTextUnicode(
| CONST LPVOID lpBuffer, | // pointer to an input buffer to be examined |
| int cb, | // the size in bytes of the input buffer |
| LPINT lpi | // pointer to flags that condition text examination and receive results |
| ); |
Parameters
lpBuffer
Pointer to the input buffer to be examined.
cb
Specifies the size, in bytes, of the input buffer pointed to by lpBuffer.
lpi
Pointer to an int that, upon entry to the function, contains a set of flags that specify the tests to be applied to the input buffer text. Upon exit from the function, that same int contains a set of bit flags indicating the results of the specified tests: 1 if the contents of the buffer pass a test, 0 for failure. Only flags that are set upon entry to the function are significant upon exit.
If lpi is NULL, the function uses all available tests to determine whether the data in the buffer is probably Unicode text.
Here are the constants used with *lpi's bit flags:
| Value | Meaning |
| IS_TEXT_UNICODE_ASCII16 | The text is Unicode, and contains nothing but zero-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 note in 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 non-printing 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, the int pointed to by 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.