LoadStringW - winuser.h. What does it do?_问答_开发者

I have been unable to find any de开发者_StackOverflowcent documentation on this function. The code base I am working with uses a function from winuser.h called LoadStringW which takes as arguments: (HINSTANCE hInstance, UINT uID, LPWSTR lpBuffer, int cchBufferMax).

What is this function? What is it for? When might it return 0?

It might be worth a mention that nearly all Win32 APIs that deal with strings have an 'A' and a 'W' variant.

The variant actually called is determined by the definition of macros that don't end in 'A' or 'W' - those macro names are what you might usually think of as the API function's name (LoadString() in this case). UNICODE builds will use the 'W' names and non-UNICODE builds will use the 'A' names.

https://learn.microsoft.com/en-us/windows/desktop/Intl/unicode-in-the-windows-api

There are times when you might want to call a Unicode version of an API even if the build isn't Unicode, in which case you just directly use the name with the 'W' tacked on to the end (it's less often necessary to need to call the non-Unicode APIs in a Unicode build, but it's just as possible). Since the non-Unicode versions of Windows are obsolete, Microsoft has started more and more to implement only Unicode versions of APIs. Note that in nearly all cases, all that the non-Unicode versions of the APIs do is to convert the ANSI/MBCS strings to Unicode, call the 'W' function, then clean up afterward.

LoadStringW is the Unicode version of LoadString.

The documentation states "If the function succeeds, the return value is the number of TCHARs copied into the buffer, not including the terminating NULL character, or zero if the string resource does not exist. To get extended error information, call GetLastError."

Here is the documentation for LoadString(): http://msdn.microsoft.com/en-us/library/ms647486%28VS.85%29.aspx

.. and here is the documentation explaining the differences between ANSI and Unicode functions in the Windows API: http://msdn.microsoft.com/en-us/library/cc500321.aspx.

Basically, the function LoadString comes in two flavours, ANSI and Unicode. LoadStringW is the Unicode-specific version of LoadString.

Edit: Just to be clear, there aren't really two completely separate functions. The ANSI version really just converts the string and calls the unicode version, which does all of the real work.

LoadStringW() is the WideCharacter version of the LoadString function.

See MSDN

It loads a widestring from a stringtable resource using the Windows Unicode Layer for Win95 and NT 3.51. See MSDN for details (see the remarks section).

For the umpteenth time, I just confirmed that when the resource compiler is instructed to null terminate the strings, the count returned by LoadString includes the terminal NULL character. I did so by examining the output buffer that I made available to LoadString.

Resource strings are not null terminated by default. In that case, the returned count excludes the terminal null character, as described in the documentation, because the null is appended by the function after the string is copied into the output buffer.

I suspect this behavior is due to the fact that LoadString disregards the fact that the resource compiler was instructed to null terminate the strings. Indeed, I suspect that it has no way of knowing that they were.

With respect to why you would want to null terminate your resource strings in the first place, when they work just fine without them, and your PE file is thereby a tad smaller, the reason is that the wide character implementation of LoadString, at the LoadStringW entry point, returns a pointer to the string, rather than copying it into a buffer, if the buffer address passed into it is a NULL pointer. Unless your strings are null terminated, using LoadString in this way produces quite unwelcome results.

Since resource strings are always stored as Unicode (wide character) strings, the ANSI implementation of LoadString cannot return a pointer, as the string must be converted to ANSI; hence, it cannot simply be copied.