c++ - VirtualAlloc failing -

i trying use virtualalloc reserve , commit block of memory , again extend block. unfortunately, returning null error error_invalid_address despite virtualquery saying address range requested free. here's code:

void* allocation = virtualalloc(null, 4096, mem_reserve | mem_commit, page_readwrite); void* desirednextallocation = (char*)allocation + 4096; memory_basic_information info; size_t memory_info = virtualquery(desirednextallocation, &info, sizeof(info)); void* extended = virtualalloc(desirednextallocation, 4096, mem_reserve | mem_commit, page_readwrite); 

the first allocation returns 0x00000000000d0000. call virtualquery results in following data in 'info':

    baseaddress 0x00000000000d1000  void *     allocationbase  0x0000000000000000  void *     allocationprotect   0x00000000  unsigned long     regionsize  0x00000000000ff000  unsigned __int64     state   0x00010000  unsigned long     protect 0x00000001  unsigned long     type    0x00000000  unsigned long 

i interpret mean there 0xff available pages beginning @ 0xd1000 in mem_free state. why attempt commit page @ 0xd1000 fail?

i'm running windows 7 , 64 bit build.

i have read several stackoverflow posts virtualalloc seem imply code should work understanding of documentation.

from documentation virtualalloc:

if memory being reserved, specified address rounded down nearest multiple of allocation granularity.

in case, address 0xd1000 rounded down address 0xd0000, reserved , hence invalid.