Data type differences between 64-bit and 32-bit programming (C + +)

C + + simply defines the relationships between these basic data types, and does not define the word length that strictly defines them. On different platforms, depending on the compiler's implementation, their word lengths are shown in the following table:

Data type	LP64	ILP64	LLP64	ILP32	LP32
Char	8	8	8	8	8
Short	16	16	16	16	16
_int32	N/A	32	N/A	N/A	N/A
Int	32	64	32	32	16
Long	64	64	32	32	32
Long Long	N/A	N/A	64	N/A	N/A
Pointer	64	64	64	32	32

In this table, LP64,ILP64,LLP64 is a word length model on a 64-bit platform, and ILP32 and LP32 are word-length models on 32-bit platforms.

LP64 means long and pointer are 64 bits, ILP64 refers to Int,long,pointer is 64 bits, LLP refers to long long and pointer is 32-bit. ILP32 refers to Int,long and pointer are 32-bit, LP32 refers to long and pointer is 32 bits.

32-bit Windows is using the ILP32 data model, and 64-bit Windows is using the LLP64 data model.

So, the biggest difference between 32-bit programming on Windows and 64-bit programming (that is, the difference between IP32 and LLP64) is that the length of the pointer is different?? Changed from 32 bits to 64 bits.

Win32 API In many cases, you need to convert integers to pointers or vice versa. There is no problem with 32-bit hardware, where the size of the pointer is the same as the integer size, but it is completely different on 64-bit hardware.

For this reason, m$ has a so-called "polymorphic type":

For specific precision, you can use a fixed-precision data type. Regardless of the processor's word size, they are the same size. Most of these types include precision in their names, as can be seen in the following table:

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

Also, use the pointer precision data type when you want the precision of the data type to vary with the size of the processor word. These types are also known as polymorphic data types. These types usually end with a _ptr suffix, as shown in the following table:

Table 2. Data type for pointer precision
Type	Defined
Dword_ptr	unsigned long type for pointer precision
Half_ptr	Half the size of the pointer. Used to contain a pointer and two small fields in the structure
Int_ptr	Signed integral type for pointer precision
Long_ptr	Signed long type of pointer precision
size_t	The maximum number of bytes that the pointer can reference. Used to count the entire range that must span the pointer
ssize_t	Signed size_t
Uhalf_ptr	unsigned half_ptr
Uint_ptr	Unsigned INT_PTR
Ulong_ptr	unsigned long_ptr
LPARAM	Synonyms with long_ptr, (defined in WTypes.h)
WPARAM	Synonyms with uint_ptr, (defined in WTypes.h)

All Win32 APIs that pass parameters or contextual information through integer parameters are changed to use these new types.

In addition, fixed-length pointers were also presented: Pointer_32 and pointer_64:

#define POINTER_32 __ptr32

#define POINTER_64 __ptr64

PS:M$DN is defined in the Basetsd.h, but is actually defined in WinNT.h.

http://blog.csdn.net/harbinzju/article/details/5785024

Data type differences between 64-bit and 32-bit programming (C + +)