DosAllocMem
From EDM2
DosAllocMem is used to allocate a private memory object, within the boundaries of the virtual-address space.
Contents
Syntax
DosAllocMem( pBaseAddress, ulObjectSize, ulAllocationFlags )
Parameters
- PPVOID pBaseAddress (output)
- This is a pointer to the variable which will receive 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 committed 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 receive 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. */ }