C++: bitset doesn't work properly

Question

I need a std::bitset<64> for my project. But while printing the number something goes wrong:

unsigned long long var = 18446462598732906495ULL;
std::cout << std::bitset<64>(var) << std::endl;

it prints:

0000000000000000000000000000000000000000000000001111111111111111

I would expect it to print:

1111111111111111000000000000000000000000000000001111111111111111

What is going wrong?

I'm working with DevC++ in 64-bit machine.

It depends if the compiler supports 64-bit integer to construct bitset. — Neil Kirk, Mar 05 '15 at 17:45
It works with c++11 [here](https://ideone.com/Dforll), and fails with C++03 [here](https://ideone.com/cE4laH). — Jarod42, Mar 05 '15 at 17:47

score 3 · Answer 1 · answered Mar 05 '15 at 17:36

3

The bitset constructor you're using takes unsigned long not unsigned long long so presumably the compiler is throwing away the bits that don't fit in unsigned long. I think you're going to have to iterate over your input value and set the bits individually.

answered Mar 05 '15 at 17:36

Mark B

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@MarkB, in C++11 constructor has ULL as a parameter, but not in C++03 – Severin Pappadeux Mar 05 '15 at 17:51

score 3 · Answer 2 · answered Mar 05 '15 at 17:41

3

As far as I can see, in C++98 bitset has 3 constructors, one of them is unsigned long (which is 32bit on Windows 64).

But! In C++11 it was rectified and constructor now has unsigned long long as a parameter (which is 64bit on Windows 64).

So, change your settings to use C++11 standard

http://www.cplusplus.com/reference/bitset/bitset/bitset/

answered Mar 05 '15 at 17:41

Severin Pappadeux

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Of course `unsigned long long` wasn't even a standard type before C++11. – chris Mar 05 '15 at 17:52

C++: bitset doesn't work properly

2 Answers2