No, you can’t. Bit field can only be used with integral type variables. C11-§6.7.2.1/5 A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed int, unsigned int, or some other implementation-defined type. Alternatively you can do this struct st { unsigned int i: 4; } arr_st[5]; but its size … Read more
If you want all bits in the test mask to match: if((value & mask) == mask) {…} If you want any single bit in the test mask to match: if((value & mask) != 0) {…} The difference is most apparent when you are testing a value for multiple things. To test for exclusion: if ((value … Read more
It’s a bitfield. It’s only valid in a struct definition, and it means that the system will only use 8 bits for your integer.
It’s allowed in all C++ compilers, that supports standard. C++03 standard 9.6/3 A bit-field shall have integral or enumeration type (3.9.1). It is implementation-defined whether a plain (neither explicitly signed nor unsigned) char, short, int or long bit-field is signed or unsigned. C++03 standard 9.6/4 If the value of an enu- merator is stored into … Read more
You cannot determine the size of bit-fields in C. You can, however, find out the size in bits of other types by using the value of CHAR_BIT, found in <limits.h>. The size in bits is simply CHAR_BIT * sizeof(type). Do not assume that a C byte is an octet, it is at least 8 bit. … Read more
You use a zero-length bitfield as a hacky way to get your compiler to lay out a structure to match some external requirement, be it another compiler’s or architecture’s notion of the layout (cross-platform data structures, such as in a binary file format) or a bit-level standard’s requirements (network packets or instruction opcodes). A real-world … Read more
For dense packing that doesn’t incur a large overhead of reading, I’d recommend a struct with bitfields. In your example where you have four values ranging from 0 to 3, you’d define the struct as follows: struct Foo { unsigned char a:2; unsigned char b:2; unsigned char c:2; unsigned char d:2; } This has a … Read more
I think you can… You’ll have to add operators for bitmasky things. I didn’t do it here but you could easily overload any relational operator. /** * */ // NOTE: I changed to a more descriptive and consistent name // This needs to be a real bitmask type. enum class file_permissions : int { no_perms … Read more
You can build a struct that conforms to the RawOptionSet protocol, and you’ll be able to use it like the built-in enum type but with bitmask functionality as well. The answer here shows how: Swift NS_OPTIONS-style bitmask enumerations.
By the C standard, the compiler is free to store the bit field pretty much in any random way it wants. You can never make any assumptions of where the bits are allocated. Here are just a few bit-field related things that are not specified by the C standard: Unspecified behavior The alignment of the … Read more