Why C++ and Python bitwise shift operator result are diffrernt?

Question

why the result of C++ and python bitwise shift operator are diffrernt?
python

>>> 1<<20
1048576

C++

cout <<1<<20;
120

cout << (1<<20);. You're not bit shifting, you're just sending '1' and '20' to cout. You're mixing the output operator and the bit shift operator. — Max
– Max, Commented Aug 14, 2020 at 15:44
In C++ you'd want this: cout << (1<<20);. C++ is a context sensitive language. The same symbols mean different things in different contexts (and can even be overloaded to gain entirely new, user-defined, meaning) — Jesper Juhl
– Jesper Juhl, Commented Aug 14, 2020 at 15:45

lubgr · Accepted Answer · 2020-08-14 15:45:00Z

5

The result differes because of the operator associativity in C++.

std::cout << 1 << 20;

is the same as

(std::cout << 1) << 20;

because operator << is left-associative. What you intend to do is

std::cout << (1 << 20);

answered Aug 14, 2020 at 15:45

lubgr

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Comments

Arun Kaliraja Baskaran · Accepted Answer · 2020-08-14 15:45:42Z

1

cout overloads the '<<' operator to print the values. So when you are doing

cout <<1<<20;

It actually prints 1 and 20 and doesnt do any shifting

int shifted = 1 << 20;
cout << shifted;

This should return the same output as python's

simpler way is to do

cout << (1 <<20);

answered Aug 14, 2020 at 15:45

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