Re: [Mingw-users] Sharing a Memory Space between two Processes

[AliReza K. M. <kho...@gm...>]

> Quoting AliReza Khoshgoftar Monfared <kho...@gm...>:
>
> >
> > Initially, I thought the solution of Shared Memory should work, as both
> > Visual Studio ,and MinGW understand CreateFileMapping(), and
> > OpenFileMapping()
> > But now I see that whatever I write to named  shared memory in visual
> > studio, I cannot read in MinGW.
> > I even tried to write a simple string like "Hello World" in Visual
> Studio,
> > and read it from the Shared Memory in MinGW, but the string isn't there
> > apparently.
>
> > So, my question:
> > *Is it possible to share a memory space between Visual Studio ,and
> > MinGW?*
>
> I don't know why you shouldn't be able to unless your perhaps you're
> using C++ semantics.  Can you give an example of what you have in
> MinGW vs what you have in VS?  This way we can see what may be wrong.
>
> --
> Earnie



Hi,

Thanks for the replies,
So, to clarify my intention, let's speak about the code,
For the time being, I am only trying to make sure I can share something
between a VC program, and a MinGW program.
Let's say, in the simplest scenario, in one , I write to a shared
memory(code is simplified with only the major function calls to avoid making
things complicated):

hMapFile = CreateFileMapping(INVALID_HANDLE_VALUE,
>         NULL,
>         PAGE_READWRITE,
>         0,
>         (DWORD)MapSize,
>         "Global\\MyFileMappingObject");
>
> hMapView = (LPSTR) MapViewOfFile(hMapFile,
>         FILE_MAP_ALL_ACCESS,
>         0,
>         0,
>         0);
>
> myString = (char *)malloc(sizeof(char)*256);
> strcpy(myString, "Hello World!!");
> CopyMemory( (PVOID)hMapView, (const VOID *)myString, (SIZE_T)WriteSize);

_getch();
> UnmapViewOfFile(hMapView);
> CloseHandle(hMapFile);
> free(myString);
>

In another, I read from the same shared memory:

hMapFile = OpenFileMapping(FILE_MAP_ALL_ACCESS,
>         FALSE,
>         "Global\\MyFileMappingObject");
> hMapView = (LPSTR) MapViewOfFile(hMapFile,
>         FILE_MAP_ALL_ACCESS, //FILE_MAP_WRITE | FILE_MAP_READ,
>         0,
>         0,
>         0);
> myString = (char *)malloc(sizeof(char)*256);
> CopyMemory( (PVOID)myString, (const VOID *)hMapView, (SIZE_T)ReadSize);
> UnmapViewOfFile(hMapView);
> CloseHandle(hMapFile);
> free(myString);


The codes do not seem to have an immediate bug, but here is the results I
get:

** If I run both codes under MSVC++, I see the exact string "Hello World" in
the second process.
**If I run both under MinGW, I see the exact string again, but the shared
memory is not cleaned for some reason (i.e. let's say after running the
codes for the first time, now I want to change the shared string to "Hi
World", I will see "Hi Worldld!!" in the second process)it only happens in
MinGW, but not in MSVC++
**If I run the first code under MSVC++, and the second under MinGW, I cannot
share anything at all (i.e both codes are compiled perfectly, but when I run
the MinGW process, I see nothing [MSVC++ process of course should be kept
open,and is.])

So, what I am asking is to know if the third test is feasible at all?
And if yes, what's wrong with my program (why the same thing works when I
run both codes in MSVC++, but doesn't when I run one in MinGW?)

Thanks
Alireza