Memory Leak using PBYTE

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I am facing a memory Leak issue :

This is my code snippet

C++

STRUCTPOINTER mystruct = NULL;
PBYTE myByte = NULL ;

mystruct = FillMyStruct();

myByte = &myStruct->BUFFER[0];

if (mystruct)
{
     VirtualFree(mystruct , 0, MEM_RELEASE);
}

Should i clear myByte Memory., how and where i should do it., i am getting memory leak in the above piece of code.

C++

// STRUCTPOINTER DEFENTION
typedef struct {

    LARGE_INTEGER myint1;
    LARGE_INTEGER myint2;
    BYTE  Buffer[1];

} MYSTRUCT, *STRUCTPOINTER ;

Posted 5-Jul-13 0:29am

gssajith87

Updated 5-Jul-13 1:12am

Jochen Arndt

v2

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nv3 · Answer 1 · 2013-07-05T02:20:00

Solution 3

You must absolutely NOT free the buffer! It is a part of MyStruct and hence is freed when MyStruct is freed.

Why do you allocate and free that structure with VirtualAlloc / VirtualFree? You probably want to use new / delete instead. And that seems to me the major problem of your code.

Posted 5-Jul-13 2:20am

nv3

Comments

pasztorpisti 6-Jul-13 16:36pm

+5, the problem is probably the use of VirtualFree(). Since he found out that there is a leak (probably because Visual Studio reported it) it is possible that the struct has been allocated by malloc/new in some way.

nv3 7-Jul-13 4:20am

Thanks! And yes, that's what I think as well. From a comment to Solution 2 I could see that he allocates the struct with VirtualAlloc. Probably copied that from some misleading example code.

CPallini · Answer 2 · 2013-07-05T00:55:00

Solution 1

At first glance you should not. However it really depends on the implementation of FillMyStruct.

Posted 5-Jul-13 0:55am

CPallini

Comments

gssajith87 5-Jul-13 7:09am

My Structure is
typedef struct {
LARGE_INTEGER StartingLcn;
LARGE_INTEGER BitmapSize;
BYTE Buffer[1];
} VOLUME_BITMAP_BUFFER, *PVOLUME_BITMAP_BUFFER;

and FillMyStruct is an IOCTL call, that fills the structure.

CPallini 5-Jul-13 7:52am

I already know the struct definition (you proved it in the OP). However I still ignore the actual FillMyStruct implementation. 'is an IOCTL call, that fills the structure' is not enough info.

wjcsharp · Answer 3 · 2013-07-05T01:11:00

Solution 2

I think, this will be decide by the implementation of FillMyStruct.
And how do you allocate the MYSTRUCT.Buffer.

Posted 5-Jul-13 1:11am

wjcsharp

Comments

gssajith87 5-Jul-13 7:19am

allocation of MyStruct.buffer is done by IOCTL CALL., FSCTL_GET_VOLUME_BITMAP

gssajith87 5-Jul-13 7:24am

This is how i do allocate memory:

mystruct = (PVOLUME_BITMAP_BUFFER) VirtualAlloc(NULL,
dwBitmapBytes + 5120, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);

This is how i fill the structure :

res = DeviceIoControl(hVolumeHandle, FSCTL_GET_VOLUME_BITMAP,
&iLCN, sizeof(iLCN), mystruct , dwinSize,
&dwOutSize, NULL);