UNICODE_STRING to std String Conversion

Question

I am using pFileObject->FileName to get the name of file opened in a kernel mode filter driver.This file name returned by this is in the form of UNICODE_STRING. I want to convert it into std String. What is the method ??? Please do provide example if possible... Below is the code

NTSTATUS FsFilterDispatchCreate(
    __in PDEVICE_OBJECT DeviceObject,
    __in PIRP           Irp
    )
{
    PFILE_OBJECT pFileObject = IoGetCurrentIrpStackLocation(Irp)->FileObject;

    DbgPrint("%wZ\n", &pFileObject->FileName);

    return FsFilterDispatchPassThrough(DeviceObject, Irp);
}

Two things you should never do in a device driver: assuming that the default *new* operator works and assuming that there's a valid code page. Do **not** use std::string in a driver. — Hans Passant, Mar 21 '13 at 18:20
As Hans noted, this plan is a non-starter. There is no MSVCR90.DLL in kernel mode. — Raymond Chen, Mar 21 '13 at 22:29
@Hans I am not planning to use std::string in KM rather i will use it in UM — Muhammad Irfan, Mar 22 '13 at 06:53

score 2 · Answer 1 · answered Mar 21 '13 at 22:25

I agree with Hans' comment. Making std:: classes work in Windows kernel mode is extremely difficult if not impossible. The default WinDDK environment is C rather than C++. Your best bet is to convert UNICODE_STRING to ANSI null-terminated string. (You can print it with DbgPrint("%s"...) etc). See example below.

UNICODE_STRING tmp;

// ...

ANSI_STRING dest;
ULONG unicodeBufferSize = tmp.Length;
// Length of unicode string in bytes must be enough to keep ANSI string
dest.Buffer = (PCHAR)ExAllocatePool(NonPagedPool, unicodeBufferSize+1);
// check for allocation failure... 
dest.Length = 0;
dest.MaximumLength = unicodeBufferSize+1;

RtlUnicodeStringToAnsiString(&dest, &tmp, FALSE);
// check for failure...
dest.Buffer[dest.Length] = 0; // now we get it in dest.Buffer

UNICODE_STRING to std String Conversion

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