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PREfast Warning 400 (Windows CE 5.0)

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400 - Using <function> to perform a case-insensitive compare to constant <string>.

This warning indicates that a case-insensitive comparison to a constant string is being performed in a locale-dependent way, when it appears that a locale-independent comparison was intended.

This warning is produced on calls to functions such as

  lstrcmpi 
  lstrcmpiA 
  lstrcmpiW

**Note   **This warning is not produced if the constant string is the empty string (_T("")) or consists only of digits or punctuation. Even though the behavior is correct in these cases, it is probably more efficient to use a case-sensitive comparison function.

String comparisons are performed in two different situations:

  • Locale-dependent

    In this situation, the comparison should match the user's language preferences.

    For example, the user wants a list of contact names in the default order for a specific language.

    In this case, a locale-dependent comparison, such as performed by lstrcmpi, or CompareString with the current locale, is appropriate.

  • Locale-independent

    In this situation, the comparison should return the same result regardless of the user's language.

    For example, the comparison determines if the extension of a file is .gif. In this case, a locale-independent comparison is appropriate.

Performing a locale-dependent comparison when a locale-independent comparison was intended can cause incorrect behavior for non-English locales. For example, in Turkish, .gif does not match .GIF; in Vietnamese, LogIn does not match LOGIN.

Usually, case-insensitive comparisons against a constant string should be performed in a locale-independent comparison. Further, names in the file system require additional considerations.

String comparisons should generally be performed with the CompareString function.

The CompareString function takes a locale as an argument; however, passing in a default locale such as the constant LOCALE_USER_DEFAULT, or the value returned from a function such as GetThreadLocale, gives different behaviors in different locales depending on the user's default.

To perform a locale-independent comparison using CompareString on Windows XP, the first parameter should be the constant LOCALE_INVARIANT.

The next code example shows how to perform a locale-independent test for whether pString matches MyGraphic.gif that ignores differences between uppercase or lowercase that also supports other operating systems.

CompareString(LOCALE_INVARIANT,
              NORM_IGNORECASE,
              pString,
              -1,
              TEXT("MyGraphic.gif"),
              -1) == 2

If code must support down-level operating systems as well, the preferred way of performing a locale-independent test is this:

     CompareString(MAKELCID(MAKELANGID(LANG_ENGLISH,
                                       SUBLANG_ENGLISH_US),
                            SORT_DEFAULT),
                   ...

PREfast considers the locale to be the default locale if it arises from any of the following constructs:

Constants

  • LOCALE_NEUTRAL   

    This constant indicates a legacy issue and gives the current user's locale instead of a language-neutral locale.

  • LOCALE_USER_DEFAULT

  • LOCALE_SYSTEM_DEFAULT

  • LANG_USER_DEFAULT

  • LANG_SYSTEM_DEFAULT

Functions

  • GetThreadLocale
  • GetUserDefaultLCID
  • GetUserDefaultLangID
  • GetUserDefaultUILanguage
  • GetSystemDefaultLCID
  • GetSystemDefaultLangID
  • GetSystemDefaultUILanguage

Example

Defective Source

return (lstrcmpi(extension,
                 TEXT("gif")) == 0);

Corrected Source

return (CompareString(LOCALE_INVARIANT,
                      NORM_IGNORECASE, 
                      extension,
                      -1,
                      TEXT ("gif"),
                      -1) == 2);

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