CODEWITHSUNDEEP
c++c++11language-lawyer
RiaD
RiaD

Reputation: 47619

Is it possible to know how many bits in integer type?

I want to use some integer type as a bit mask. I want to know for which n it's guaranteed that any number from 0 to 2^n-1 is avaliablle in this type. (Actually I'm going to use uintmax_t)

I know it's usually 8 * sizeof(uintmax_t) (or probably CHAR_BIT * sizeof(uintmax_t)), but I guess it isn't guaranteed.

So I want, to find this n other way.

How do I achieve this?

Upvotes: 1

Views: 675

Answers (3)

PaperBirdMaster
PaperBirdMaster

Reputation: 13320

Use the cstdint include.

It provides cross-platform fixed-size typedefs for integer types and macro constants for its limits.

#include <cstdint>
std::int8_t Signed = 0;    // granted to 8bit size.
std::uint8_t Unsigned = 0; // granted to 8bit size.
Signed = INT8_MAX;        // store the max value for a signed 8bit value.
Unsigned = UINT8_MAX;      // store the max value for an unsigned 8bit value.

Hope it helps.

Upvotes: 2

Aki Suihkonen
Aki Suihkonen

Reputation: 20027

The answer would be 1+log2((UINTMAX_MAX>>1)+1)

It can also be derived by counting bits with repeated shifting.

Upvotes: 1

juanchopanza
juanchopanza

Reputation: 227370

There is nothing wrong with using the sizeof operator in combination with CHAR_BIT

const std::size_t nBits = CHAR_BIT * sizeof(some_integer_type);

This would also work for other built-int types, as well as user defined types.

Upvotes: 4

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