why VirtualQuery return 0 sometimes?

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Hi,
sometimes when using the VirtualQuery function the return value is 0, it depends on the

VB

dwLength

paramter.

1. i used VirtualAlloc function to alloc 1 mbyte of memory

MIDL

pMem = VirtualAlloc(NULL, nAllocatedSize, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);

nAllocatedSize size is 1024*1024 (1MB)

2. i just what to view the status of the memory by

MEMORY_BASIC_INFORMATION meminfo;
DWORD size = VirtualQuery(pMem2,&meminfo,m_param1);

when i call that function with m_param1>8192 the return value is 0
and m_param1<8192 the value is 48, i did'nt used any of the memory i think it should return 1048576 becuase the attributes of all pages should be the some? no?

Thanks

Posted 18-Aug-10 21:09pm

pascal.schwartz

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Eugen Podsypalnikov 19-Aug-10 5:58am

The returned value =sizeof(MEMORY_BASIC_INFORMATION)
or 0 (may be due to Windows >= 6.0 security checks) :)
Have you an XP platform to test it also there ?

2 solutions

Solution 1

The VirtualQuery function doesn't return the size of the memory you are querying. It returns the size of the buffer it has populated (meminfo in your case).

A return code of 0 indicates an error, and you'll need to call GetLastError() to find out more information.

Posted 19-Aug-10 23:29pm

Electron Shepherd

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Tsuda Kageyu · Accepted Answer · 2010-08-20T00:03:00

Solution 2

Maybe you're misunderstanding the role of dwLength.
dwLength is the size of the buffer for MEMORY_BASIC_INFORMATION.
So you shouldn't let it greater than sizeof(MEMORY_BASIC_INFORMATION).

You'd better do like this.

C++

MEMORY_BASIC_INFORMATION meminfo;
SIZE_T size = VirtualQuery(pMem2, &meminfo, sizeof(MEMORY_BASIC_INFORMATION));

Posted 20-Aug-10 0:03am

Tsuda Kageyu

Comments

pascal.schwartz 22-Aug-10 2:35am

Thank , you are right i was confused about the dwLength.
now it works