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#186 in FFI

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abibool - C ABI compatible boolean types

GitHub crates.io docs.rs License Build Status

For most sane rust APIs, you should prefer bool in your interfaces and simply convert between types. However, bool isn't legal for all bit patterns, making it unusable for most FFI without conversions. For simple FFI, this isn't a problem, but C APIs writing arrays of BOOL or BOOLEAN, or structures containing these types, become problematic and require allocations and copies to avoid undefined behavior. Alternatively, you could just use integer types, that can obfuscate intent and result in bugs if multiple truthy-but-different value are directly compared when you expect boolean logic.

Type Map

Note that this is incredibly system specific. E.g. BOOL for windows is 4 bytes, but for OS X it's 1 byte... probably.
When using abibool to write FFI crates, you may wish to cc a bunch of static_asserts in a build script to validate the size of your underlying C types.

C / C++ type abibool type notes
bool (C++) varies Often 1 byte, but sometimes 4 or worse
_Bool (C99 / stdbool.h) varies Often 1 byte, but sometimes 4 or worse
BOOLEAN (Win32) b8 / bool8
BOOL (Win32) b32 / bool32
BOOL (OS X / objc.h) b8 / bool8 ? Typically signed char, but sometimes bool or unsigned char
jboolean (Java / JNI) b8 / bool8



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