CODEWITHSUNDEEP
c++algorithminteger
Anubhav Sachan
Anubhav Sachan

Reputation: 31

calculate size of an integer/any data type without using `sizeof(*type)`?

Is there a method to calculate the size of a variable without using any predefined functions? I read somewhere that it can be done using bit manipulation, but I'm not sure.

This is an answer (finding the size of integer without using sizeof), but I want a better approach in C++ which shall be algorithmic (without using a predefined function.

Upvotes: 0

Views: 277

Answers (1)

eerorika
eerorika

Reputation: 238401

Is there a method to calculate the size of a variable without using any predefined functions?

Yes. You can use the sizeof operator. sizeof is not a function.

calculate size of an integer/any data type without using sizeof(*type)?

If you have an object of such type, then pointer arithmetic is one way. There is an example of this in the page linked in the question. But there is generally no need to use such hack.

Another - limited - trick is to use std::numeric_limits (although its implementation probably internally uses sizeof). This works only with integer types (assuming no padding bits; will work for unsigned integers, may in theory fail with signed ones):

using T = int; // example
static_assert(std::is_integral_v<T> &&
              std::has_unique_object_representations_v<T>);
auto size = ( std::numeric_limits<T>::digits
            + std::numeric_limits<T>::is_signed) / CHAR_BIT;

but I want a better approach

sizeof operator is the better approach, compared to the tricks mentioned above.

Upvotes: 1

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