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 |
); |
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.
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. |
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 |
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.
FoldString, GetSystemDefaultLCID, GetUserDefaultLCID, LCMapString, lstrcmp, lstrcmpi, MAKELCID
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