ILP32 and LP64 data models and data type sizes

Table 1 compares data models and data type sizes of ILP32 and LP64 environments.

Table 1. Comparison of ILP32 and LP64 data models
ILP32 (32-bit environment)	LP64 (64-bit environment)
Data model ILP32 (32-bit pointer)	Data model LP64 (64-bit pointer)
`int`, `long`, `ptr`, and `off_t` are all 32 bits (4 bytes) in size.	`int` is 32 bits in size. `long`, `ptr`, and `off_t` are all 64 bits (8 bytes) in size.

The 32-bit data model for z/OS XL C/C++ compilers is ILP32 plus long long. This data model uses the 4/4/4 data type size model and includes a long long type. Table 2 compares the type sizes for the different models.

LP64 is the 64-bit data model chosen by the Aspen working group (formed by X/OPEN and a consortium of hardware vendors). LP64 is short for long-pointer 64. It is commonly referred to as the 4/8/8 data type size model and includes the integer/long/pointer type sizes, measured in bytes.

Table 2. ILP32 and LP64 type size comparisons for signed and unsigned data types
Data Type	32-bit sizes (in bytes)	64-bit sizes (in bytes)	Remarks
char	1	1
short	2	2
int	4	4
long	4	8
long long	8	8
float	4	4
double	8	8
long double	16	16
pointer	4	8
wchar_t	2	4	Other UNIX platforms usually have wchar_t 4 bytes for both 32-bit and 64-bit mode.
size_t	4	8	This is an unsigned type.
ptrdiff_t	4	8	This is a signed type.