DosAllocMem

DosAllocMem is used to allocate a private memory object, within the boundaries of the virtual-address space.

Syntax

DosAllocMem( pBaseAddress, ulObjectSize, ulAllocationFlags )

Parameters

PPVOID pBaseAddress (output): This is a pointer to the variable which will recieve the base address of the allocated private memory object.
ULONG ulObjectSize (input): The size in bytes of the memory block you want to allocate. This will, by the system, be rounded up to the next page-size boundary.
ULONG ulAllocationFlags (input): Flags used to describe allocation attributes, as well as access protection of the private memory block.

Allocation attributes

PAG_COMMIT (0x00000010) makes all private memory blocks initially committed.

OBJ_TILE (0x00000040) forces the memory block to be allocated in the first 512MB of virtual-address space. Mapping the memory block is done with the 16-bit selectors. The following table shows how a 32-bit memory block is mapped using 16-bit selectors.

32bit Offset	16bit alias selectors
BaseAddress+000KB	Sel
BaseAddress+064KB	Sel + HugeInc
BaseAddress+128KB	Sel + HugeInc * 2
...	...

HugeInc is the same huge increment that is used by DosAllocHuge.

Access protection

PAG_EXECUTE (0x00000004) tells the system that 'execute access' to the commited pages is desired in the memory block.

PAG_READ (0x00000001) tells the system that 'read access' is desired.

PAG_WRITE (0x00000002) tells the system that 'write access' is desired.

PAG_GUARD (0x00000008) tells the system that an access to the committed pages should cause a guard page exception to be raised.

At least one of PAG_EXECUTE, PAG_WRITE or PAG_READ must be set.

Returns

APIRET rc

The following values can be returned:

0	NO_ERROR
8	ERROR_NOT_ENOUGH_MEMORY
87	ERROR_INVALID_PARAMETER
95	ERROR_INTERRUPT

Sample Code

 
#define INCL_DOSMEMMGR
#include <os2.h>
#include <bsememf.h> /* This will get the memory managment flags */

PVOID BaseAddress;      /* Pointer to the allocated memory block  */
ULONG ObjectSize;       /* The requested size of the memory block */
ULONG AllocationFlags;  /* Flags                                  */
APIRET rc;              /* Will recieve the return code           */

   ObjectSize = 9000;   /* Asking for 9000 bytes, this will */
                        /* rounded up to 12KB.              */

   AllocationFlags = PAG_WRITE | PAG_EXECUTE;
            /* Allows read/write to the memory block, but */
            /* the block isn't committed within memory    */
            /* yet.                                       */

   rc = DosAllocMem(&BaseAddress, ObjectSize, AllocationFlags);

   if ( rc != 0)
   {
     /* We have an error we must take care of. */
   }