CompareString info  Overview  Group

The CompareString function compares two character strings, using the locale specified by the given identifier as the basis for the comparison.

int CompareString(

LCID Locale,	// locale identifier
DWORD dwCmpFlags,	// comparison-style options
LPCTSTR lpString1,	// pointer to first string
int cchCount1,	// size, in bytes or characters, of first string
LPCTSTR lpString2,	// pointer to second string
int cchCount2	// size, in bytes or characters, of second string
);

Parameters

Locale

Specifies the locale used for the comparison. This parameter can be one of the following predefined locale identifiers:

Value	Meaning
LOCALE_SYSTEM_DEFAULT	The system’s default locale.
LOCALE_USER_DEFAULT	The current user’s default locale.

This parameter can also be a locale identifier created by the MAKELCID macro.

dwCmpFlags

A set of flags that indicate how the function compares the two strings. By default, these flags are not set. This parameter can specify zero to get the default behavior, or it can be any combination of the following values:

Value	Meaning
NORM_IGNORECASE	Ignore case.
NORM_IGNOREKANATYPE	Do not differentiate between Hiragana and Katakana characters. Corresponding Hiragana and Katakana characters compare as equal.
NORM_IGNORENONSPACE	Ignore nonspacing characters.
NORM_IGNORESYMBOLS	Ignore symbols.
NORM_IGNOREWIDTH	Do not differentiate between a single-byte character and the same character as a double-byte character.
SORT_STRINGSORT	Treat punctuation the same as symbols.

lpString1

Points to the first string to be compared.

cchCount1

Specifies the size, in bytes (ANSI version) or characters (Unicode version), of the string pointed to by the lpString1 parameter. If this parameter is - 1, the string is assumed to be null terminated and the length is calculated automatically.

lpString2

Points to the second string to be compared.

cchCount2

Specifies the size, in bytes (ANSI version) or characters (Unicode version), of the string pointed to by the lpString2 parameter. If this parameter is - 1, the string is assumed to be null terminated and the length is calculated automatically.

Return Values

If the function succeeds, the return value is one of the following values:

Value	Meaning
CSTR_LESS_THAN	The string pointed to by the lpString1 parameter is less in lexical value than the string pointed to by the lpString2 parameter.
CSTR_EQUAL	The string pointed to by lpString1 is equal in lexical value to the string pointed to by lpString2.
CSTR_GREATER_THAN	The string pointed to by lpString1 is greater in lexical value than the string pointed to by lpString2.

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_INVALID_FLAGS

ERROR_INVALID_PARAMETER

Remarks

Notice that if the return value is 2, the two strings are “equal” in the collation sense, though not necessarily identical.

To maintain the C run-time convention of comparing strings, the value 2 can be subtracted from a nonzero return value. The meaning of < 0, ==0 and > 0 is then consistent with the C run times.

If the two strings are of different lengths, they are compared up to the length of the shortest one. If they are equal to that point, then the return value will indicate that the longer string is greater. For more information about locale identifiers, see Locale Identifiers.

Typically, strings are compared using what is called a “word sort” technique. In a word sort, all punctuation marks and other nonalphanumeric characters, except for the hyphen and the apostrophe, come before any alphanumeric character. The hyphen and the apostrophe are treated differently than the other nonalphanumeric symbols, in order to ensure that words such as “coop” and “co-op” stay together within a sorted list.

If the SORT_STRINGSORT flag is specified, strings are compared using what is called a “string sort” technique. In a string sort, the hyphen and apostrophe are treated just like any other nonalphanumeric symbols: they come before the alphanumeric symbols.

The following table shows a list of words sorted both ways:

Word Sort	String Sort		Word Sort	String Sort
billet	bill’s		t-ant	t-ant
bills	billet		tanya	t-aria
bill’s	bills		t-aria	tanya
cannot	can’t		sued	sue’s
cant	cannot		sues	sued
can’t	cant		sue’s	sues
con	co-op		went	we’re
coop	con		were	went
co-op	coop		we’re	were

The lstrcmp and lstrcmpi functions use a word sort. The CompareString and LCMapString functions default to using a word sort, but use a string sort if their caller sets the SORT_STRINGSORT flag.

The CompareString function is optimized to run at the highest speed when dwCmpFlags is set to 0 or NORM_IGNORECASE, and cchCount1 and cchCount2 have the value -1.

The CompareString function ignores Arabic Kashidas during the comparison. Thus, if two strings are identical save for the presence of Kashidas, CompareString returns a value of 2; the strings are considered "equal" in the collation sense, though they are not necessarily identical.

See Also

FoldString, GetSystemDefaultLCID, GetUserDefaultLCID, LCMapString, lstrcmp, lstrcmpi, MAKELCID