Understanding the Bit Size of 'long' on 64-bit Windows
Question:
Conlicting information suggests that 'long' may not be 64 bits on 64-bit Windows machines. Is this true, and what should programmers use instead?
Answer:
The answer lies in examining different integer size arrangements on 64-bit platforms:
ILP64 (Int, Long, Pointers Are 64-bit)
- All integer data types and pointers are 64 bits.
LP64 (Long, Pointers Are 64-bit)
- Long and pointer types are 64 bits.
- Int and other integer types remain 32 bits.
LLP64 (Long Long, Pointers Are 64-bit)
- This is the scheme used by Microsoft in 64-bit Windows.
- Long long and pointer types are 64 bits.
- Int and long remain 32 bits.
Implications for Windows:
On 64-bit Windows, 'long' is indeed 32 bits, unlike on other 64-bit platforms. Microsoft adopted the LLP64 scheme to ensure compatibility with existing 32-bit applications.
Recommendations:
To ensure platform-neutral code, use integer types from the
- int32_t for 32-bit integers
- int64_t for 64-bit integers
- uintptr_t for pointers
Be cautious when using system types (e.g., 'long') as they may vary across platforms. Only use intptr_t as the result of subtracting two uintptr_t values.
Conclusion:
The bit size of 'long' on 64-bit Windows is 32 bits, deviating from the LP64 scheme used by many other 64-bit systems. To avoid platform-specific complications, programmers should adopt platform-neutral integer types and carefully handle system types.
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