CompareString

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
Pointer 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
Pointer 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.

Windows CE: Windows CE does not support the ANSI version of this function.

Windows CE does not support the following values for the dwCmpFlags parameter:

NORM_IGNOREKANATYPE

NORM_IGNORENONSPACE

NORM_IGNORESYMBOLS

NORM_IGNOREWIDTH

The dwCmpflags parameter always includes the SORT_STRINGSORT value.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Requires version 1.0 or later.
  Header: Declared in winnls.h.
  Import Library: Use kernel32.lib.
  Unicode: Implemented as Unicode and ANSI versions on Windows NT.

See Also

String Manipulation Overview, String Manipulation Functions, FoldString, GetSystemDefaultLCID, GetUserDefaultLCID, LCMapString, lstrcmp, lstrcmpi, MAKELCID