How to "compose" a number knowing its bits value in C/C++

Asked Feb 24 '19 at 09:43

Active Feb 24 '19 at 09:48

Viewed 64 times

I want to compose a 1-byte (unsigned char) number, knowing its bits value.

For example, 7th and 6th are always 0 and 1 respectively, values of 5th to 3rd are stored in three other variables, and 2nd to 0th bits shall take a value stored in one variable, e.g. decimal 5.

At first I fought I can create an array of 8 elements, to store each bit, then convert it to a decimal number using custom bin2dec, but the problem is 1) I don't want to use additional "self-written" functions, 2) I'm not sure, how to put value 5 there (it looks like I need to dec2bin at first).

I can solve this problem using SystemC, but I'm interested how to do it using C/C++ methods (without additional downloaded libs).

asked Feb 24 '19 at 09:43

ans

Look up bit shifting. – Fredrik Feb 24 '19 at 09:45
2

`number = (0 << 7) | (1 << 6) | (v5 << 5) | (v3 << 3) | v20;` – pmg Feb 24 '19 at 09:45
Why not use [`std::bitset`](https://en.cppreference.com/w/cpp/utility/bitset) – Mohit Feb 24 '19 at 09:47
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@Fredrik But they tagged it as a `c++`. – Mohit Feb 24 '19 at 09:51
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@Fredrik I don't see it. Where? – melpomene Feb 24 '19 at 09:52
It’s in the title.. – Fredrik Feb 24 '19 at 09:52
@Fredrik ... no? I mean, what do you mean? – melpomene Feb 24 '19 at 09:53
The title literally says ”in C/C++” – Fredrik Feb 24 '19 at 09:54
1

@Fredrik Yes, exactly. "C/C++" is not a thing, so we can argue what exactly it means, but I'm sure it does not mean "the intersection of C and C++". When someone puts "C/C++" on their resume, it probably does not mean "I know the parts that C and C++ have in common". – melpomene Feb 24 '19 at 09:57

How to "compose" a number knowing its bits value in C/C++

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