C++变量在32位系统和64位系统的区别

Let's describe here only types which can be of interest for developers when porting applications. These types are shown in Table 3. Most recompilation errors will relate to using these very types.

Type	Type's size on x32 / x64 platform	Note
int	32 / 32	Basic type. On 64-bit systems remains 32-bit.
long	32 / 32	Basic type. On 64-bit Windows systems remains 32-bit. Keep in mind that in 64-bit Linux systems this type was extended to 64-bit. Don't forget about it if you develop code which should be compiled for Windows and Linux systems.
size_t	32 / 64	Basic unsigned type. The type's size is chosen in such a way that you could write the maximum size of a theoretically possible array into it. You can safely put a pointer into size_t type (except for pointers to class functions, but this is a special case).
ptrdiff_t	32 / 64	Similar to size_t type but this is a signed type. The result of the expression where one pointer is subtracted from the other (ptr1-ptr2) will have ptrdiff_t type.
Pointer	32 / 64	The size of the pointer directly depends on the platform's size. Be careful while converting pointers to other types.
__int64	64 / 64	Signed 64-bit type.
DWORD	32 / 32	32-bit unsigned type. In WinDef.h is defined as:typedef unsigned long DWORD;
DWORDLONG	64 / 64	64-bit unsigned type. In WinNT.h is defined as:typedef ULONGLONG DWORDLONG;
DWORD_PTR	32 / 64	Unsigned type in which a pointer can be placed. In BaseTsd.h is defined as:typedef ULONG_PTR DWORD_PTR;
DWORD32	32 / 32	32-bit unsigned type. In BaseTsd.h is defined as:typedef unsigned int DWORD32;
DWORD64	64 / 64	64-bit unsigned type. In BaseTsd.h is defined as:typedef unsigned __int64 DWORD64;
HALF_PTR	16 / 32	A half of a pointer. In Basetsd.h is defined as:#ifdef _WIN64 typedef int HALF_PTR;#else typedef short HALF_PTR;#endif
INT_PTR	32 / 64	Signed type in which a pointer can be placed. In BaseTsd.h is defined as:#if defined(_WIN64) typedef __int64 INT_PTR; #else typedef int INT_PTR;#endif
LONG	32 / 32	Signed type which remained 32-bit. That's why in many cases LONG_PTR now should be used. In WinNT.h is defined as:typedef long LONG;
LONG_PTR	32 / 64	Signed type in which a pointer can be placed. In BaseTsd.h is defined as:#if defined(_WIN64) typedef __int64 LONG_PTR; #else typedef long LONG_PTR;#endif
LPARAM	32 / 64	Parameter for sending messages. In WinNT.h is defined as:typedef LONG_PTR LPARAM;
SIZE_T	32 / 64	Analog of size_t type. In BaseTsd.h is defined as:typedef ULONG_PTR SIZE_T;
SSIZE_T	32 / 64	Analog of ptrdiff_t type. In BaseTsd.h is defined as:typedef LONG_PTR SSIZE_T;
ULONG_PTR	32 / 64	Unsigned type in which a pointer can be placed. In BaseTsd.h is defined as:#if defined(_WIN64) typedef unsigned __int64 ULONG_PTR;#else typedef unsigned long ULONG_PTR;#endif
WORD	16 / 16	Unsigned 16-bit type. In WinDef.h is defined as:typedef unsigned short WORD;
WPARAM	32 / 64	Parameter for sending messages. In WinDef.h is defined as:typedef UINT_PTR WPARAM;

Table 3. Types to be noted while porting 32-bit programs on 64-bit Windows systems.