What is the correct/preferred way to handle parameters of type PWSTR in JNA on Windows

[Kustaa Nyholm]

For example CM_Get_Device_ID:

https://msdn.microsoft.com/en-us/library/windows/hardware/ff538405(v=vs.85).aspx



CMAPI
CONFIGRET
WINAPI CM_Get_Device_ID(
_In_ DEVINST dnDevInst,
_Out_ PWSTR Buffer,
_In_ ULONG BufferLen,
_In_ ULONG ulFlags
);



My current mapping is

int CM_Get_Device_IDA(int dnDevInst, byte[] Buffer, int BufferLen, int ulFlags);

which works.

However this leaves open the question of character encoding for the returned string (Buffer)
and what happens if it contains wide characters (don't know if in this particular instance this
is worry).

I can of course use the CM_Get_Device_IDW

int CM_Get_Device_IDW(int dnDevInst, byte[] Buffer, int BufferLen, int ulFlags);

or perhaps:

int CM_Get_Device_IDW(int dnDevInst, char[] Buffer, int BufferLen, int ulFlags);

but what is the preferred way, I read that JNA handles wide ASCII/UNICODE conversion

automatically (awesome) but I can't figure out all the details, this must be documented
somewhere but I can't find it. I found this:

https://github.com/java-native-access/jna/issues/377

but it doesn't really clarify this for me. Maybe it is just me.

Am I correct that if I specify W32APIOptions.UNICODE_OPTIONS when loading the library
I can always map PWSTR to char[] if the function is writing that parameter or
use String if the function is just taking the string in or returns it?

So how do I turn this (char[]) into a String in the preferred way?

JNA Native has toString(char[]) function but some Windows API functions take
an oversize buffer and return the length of the string but there is no

Native.toString(char[] chars,int offset, int len)

Of course there is

String(char[] chars,int offset, int len)

but as no encoding is mentioned I'm left in doubt. I suppose JNA maybe
clever enough to handle the encoding (if it is an issue) when it
passes and retrieves the char[] parameters?


cheers Kusti









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[Timothy Wall]

You can use `char[]` with `Native.toString(char[])` or `Memory` with `Pointer.getWideString(0)`. In either case, JNA will terminate the string when it finds a NUL terminator.

PWSTR is likely _always_ defined to `wchar_t*`, so you probably don’t have to worry about byte strings. When you’re using wchar_t, there is no encoding involved.

If you should happen upon a byte string that needs decoding, `Native.toString()` has a variant where you can provide an encoding name.

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