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Questions tagged [bit-fields]

A bit field is used to compactly store multiple logical values as a short series of bits where each of the single bits can be addressed separately.

A bit field is used to represent and store a set of known width and logically grouped set of values. These fields can then be addressed individually in the code. A common use of such a construct is flags.

In language such as C and C++, bit fields can also be used to abstract and interop with specific hardware.

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Is it safe to use -1 to set all bits to true?

I've seen this pattern used a lot in C & C++. unsigned int flags = -1; // all bits are true Is this a good portable way to accomplish this? Or is using 0xffffffff or ~0 better?
hyperlogic
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Why is assigning a value to a bit field not giving the same value back?

I saw the below code in this Quora post: #include struct mystruct { int enabled:1; }; int main() { struct mystruct s; s.enabled = 1; if(s.enabled == 1) printf("Is enabled\n"); // --> we think this to be printed else …
iammilind
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Bit fields in C#

I have a structure which I need to populate and write to disk (several actually). An example is: byte-6 bit0 - original_or_copy bit1 - copyright bit2 - data_alignment_indicator bit3 - PES_priority bit4-bit5 - PES_scrambling control. …
Rob
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Why bit endianness is an issue in bitfields?

Any portable code that uses bitfields seems to distinguish between little- and big-endian platforms. See the declaration of struct iphdr in linux kernel for an example of such code. I fail to understand why bit endianness is an issue at all. As far…
Leonid99
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Storing 8 logical true/false values inside 1 byte?

I'm working on a microcontroller with only 2KB of SRAM and desperately need to conserve some memory. Trying to work out how I can put 8 0/1 values into a single byte using a bitfield but can't quite work it out. struct Bits { int8_t b0:1, b1:1,…
Jazcash
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What does 'unsigned temp:3' in a struct or union mean?

Possible Duplicate: What does this C++ code mean? I'm trying to map a C structure to Java using JNA. I came across something that I've never seen. The struct definition is as follows: struct op { unsigned op_type:9; //---> what does this…
Munir Ahmed
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What does a colon in a struct declaration mean, such as :1, :7, :16, or :32?

What does the following C++ code mean? unsigned char a : 1; unsigned char b : 7; I guess it creates two char a and b, and both of them should be one byte long, but I have no idea what the ": 1" and ": 7" part does.
derrdji
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When is it worthwhile to use bit fields?

Is it worthwhile using C's bit-field implementation? If so, when is it ever used? I was looking through some emulator code and it looks like the registers for the chips are not being implemented using bit fields. Is this something that is avoided…
Russel
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Does Python have a bitfield type?

I need a compact representation of an array of booleans, does Python have a builtin bitfield type or will I need to find an alternate solution?
Gordon Wrigley
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In C, what does a colon mean inside a declaration?

Possible Duplicate: What does ‘unsigned temp:3’ means I'm learning some kernel code, and came along the following line (in linux 2.4, sched.h, struct mm_struct): unsigned dumpable:1; What does this mean?
Tzafrir
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How is the size of a struct with Bit Fields determined/measured?

#include typedef struct size { unsigned int a:1; unsigned int b:31; unsigned int c:1; } mystruct; int main() { mystruct a; printf("%d", sizeof(a)); return 0; } With int b:31, the output…
Jagan
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C++ bitfield packing with bools

I've just done a test with bitfields, and the results are surprising me. class test1 { public: bool test_a:1; bool test_b:1; bool test_c:1; bool test_d:1; bool test_e:1; bool test_f:1; bool test_g:1; bool…
Roddy
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Declaring and using a bit field enum in Swift

How should bit fields be declared and used in Swift? Declaring an enum like this does work, but trying to OR 2 values together fails to compile: enum MyEnum: Int { case One = 0x01 case Two = 0x02 case Four = 0x04 case…
Pascal Bourque
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C++11 standard conformant bitmasks using enum class

Can you implement standard conformant (as described in 17.5.2.1.3 of the n3242 draft) type safe bitmasks using enum class? The way I read it, a type T is a bitmask if it supports the |,&,^,~,|=,&= and ^= operators and further you can do if(l&r)…
B.S.
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Practical Use of Zero-Length Bitfields

I am not totally sure about C, but C++ allows unnamed bit-fields of 0 length. For example: struct X { int : 0; }; Question one: What practical uses of this can you think of? Question two: What real-world practical uses (if any) are you aware…
Armen Tsirunyan
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