C++ Bitfields const expressions

Asked Feb 28 '18 at 00:09

Active Feb 28 '18 at 00:09

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I recently was code generating some bitfields and I was using const expressions to fill out the bitfield. (C++ 03)

I'm wondering a few things. 1. Is this a good idea. 2. Is this guranteed by GCC. 3. Is this going to work (it compiles, waiting to test).

const uint16_t bitSize = 5;
struct MyStruct
{
    uint32_t myfield : bitSize;
};

asked Feb 28 '18 at 00:09

Michael Stephens

1. matter of taste, 2. yes if is included 3. yes – Öö Tiib Feb 28 '18 at 00:36
@ÖöTiib: Why are you answering in the comments section? – Lightness Races in Orbit Feb 28 '18 at 00:46
2

_"waiting to test"_ Please wait to ask, until you have tested it. – Lightness Races in Orbit Feb 28 '18 at 00:46
Unrelated to your question - Why do you specifically want `bitSize` to be 16 bits? Any old integer type can hold values up to 32. – Bo Persson Feb 28 '18 at 01:05
making an assumption as to what you want, but if you do want a packed bitfield with gcc then at the end of your struct you should [`}__attribute__((packed));`](https://stackoverflow.com/questions/25822679/packed-bit-fields-in-c-structures-gcc) – Justin Randall Feb 28 '18 at 01:47
@LightnessRacesinOrbit since ok,yes,yes is not too useful answer but I had no time to elaborate. – Öö Tiib Feb 28 '18 at 13:35
@ÖöTiib Not a good reason – Lightness Races in Orbit Feb 28 '18 at 14:50

0 Answers0