Is `long` Really 64-Bits on 64-Bit Windows?

Bit Size of Long on 64-Bit Windows: A Closer Look

The question of the size of long on 64-bit Windows has sparked some confusion. While documentation suggests that long is indeed 64-bits in this environment, the reality is more nuanced.

In the realm of Unix systems, there are various arrangements for integer and pointer sizes on 64-bit platforms, mainly ILP64 and LP64. However, Microsoft's approach differs with LLP64.

ILP64 vs. LP64

Type	ILP64	LP64	LLP64
char	8	8	8
short	16	16	16
int	64	32	32
long	64	64	32
long long	64	64	64
pointer	64	64	64

All modern 64-bit Unix systems use LP64, where long is 64-bits. MacOS X and Linux fall under this category.

LLP64 and 64-Bit Windows

Microsoft's LLP64 scheme prioritizes recompiling 32-bit software without modifications. Consequently, on 64-bit Windows systems:

• long and int remain 32-bit in size
• New data types are introduced for 64-bit integers

Platform-Neutral Code

To achieve platform-neutral code, it is recommended to use types from the C99 header, which provides:

• int8_t to int64_t for signed integers
• uintptr_t for unsigned integers to store pointers
• intmax_t for the largest integer size on the platform

By using these types in your code, you can write applications that are independent of the specific integer sizes on different platforms.

Conclusion

While long is typically 64-bits onUnix systems, on 64-bit Windows, it remains 32-bits due to Microsoft's LLP64 approach. By understanding the different integer size conventions and using platform-neutral types, developers can create code that is compatible across a wide range of systems.

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