| Platform SDK: Win64 Programming Preview |
[This is preliminary documentation and subject to change.]
There are three classes of new data types: fixed-precision data types, pointer-precision types, and specific-precision pointers. These types were added to the Windows environment (specifically, to Basetsd.h) to allow developers to prepare for 64-bit Windows well before its introduction. These new types were derived from the basic C-language integer and long types, so they work in existing code. Therefore, use these data types in your code now, test your code as a Win32-based application, and recompile as a Win64-based application when 64-bit Windows is available.
In addition, adopting these new data types will make your code more robust. To use these data types, you must scan your code for potentially unsafe pointer usage, polymorphism, and data definitions. To be safe, use the new types. For example, when a variable is of type ULONG_PTR, it is clear that it will be used for casting pointers for arithmetic operations or polymorphism. It is not possible to indicate such usage directly by using the native Win32 data types. You can do this by using derived type naming or Hungarian notation, but both techniques are prone to errors.
Fixed-precision data types are the same length in both Win32 and Win64 programming. To help you remember this, their precision is part of the name of the data type. The following are the fixed-precision data types.
| Type | Definition |
|---|---|
| DWORD32 | 32-bit unsigned integer |
| DWORD64 | 64-bit unsigned integer |
| INT32 | 32-bit signed integer |
| INT64 | 64-bit signed integer |
| LONG32 | 32-bit signed integer |
| LONG64 | 64-bit signed integer |
| UINT32 | Unsigned INT32 |
| UINT64 | Unsigned INT64 |
| ULONG32 | Unsigned LONG32 |
| ULONG64 | Unsigned LONG64 |
As the pointer precision changes (that is, as it becomes 32 bits with Win32 code and 64 bits with Win64 code), these data types reflect the precision accordingly. Therefore, it is safe to cast a pointer to one of these types when performing pointer arithmetic; if the pointer precision is 64 bits, the type is 64 bits. The count types also reflect the maximum size to which a pointer can refer. The following are the pointer-precision and count types.
| Type | Definition |
|---|---|
| DWORD_PTR | Unsigned long type for pointer precision. |
| HALF_PTR | Half the size of a pointer. Use within a structure that contains a pointer and two small fields. |
| INT_PTR | Signed integral type for pointer precision. |
| LONG_PTR | Signed long type for pointer precision. |
| SIZE_T | The maximum number of bytes to which a pointer can refer. Use for a count that must span the full range of a pointer. |
| SSIZE_T | Signed SIZE_T. |
| UHALF_PTR | Unsigned HALF_PTR. |
| UINT_PTR | Unsigned INT_PTR. |
| ULONG_PTR | Unsigned LONG_PTR. |
There are also new pointer types that explicitly size the pointer. Be cautious when using pointers in 64-bit code: If you declare the pointer using a 32-bit type, the system creates the pointer by truncating a 64-bit pointer. (All pointers are 64 bits on a 64-bit platform.)
| Type | Definition |
|---|---|
| POINTER_32 | A 32-bit pointer. On a 32-bit system, this is a native pointer. On a 64-bit system, this is a truncated 64-bit pointer. |
| POINTER_64 | A 64-bit pointer. On a 64-bit system, this is a native pointer. On a 32-bit system, this is a sign-extended 32-bit pointer.
Note that it is not safe to assume the state of the high pointer bit. |