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Shift Operators: >> and <<

Updated: May 2011

expression << expression
expression >> expression

The bitwise shift operators are as follows:

  • Right shift (>>)

  • Left shift (<<)

Both operands of the shift operators must be of integral types. Integral promotions are performed according to the rules described in Integral Promotions. The type of the result is the same as the type of the promoted left operand. The value of a right-shift expression x >> y is x / 2y, and the value of a left-shift expression x << y is x * 2y.

The result is undefined if the right operand of a shift expression is negative or if the right operand is greater than or equal to the number of bits in the (promoted) left operand.

The left-shift operator causes the bit pattern in the first operand to be shifted to the left by the number of bits specified by the second operand. Bits vacated by the shift operation are zero-filled. This is a logical shift instead of a shift-and-rotate operation.

The right-shift operator causes the bit pattern in the first operand to be shifted to the right by the number of bits specified by the second operand. Bits vacated by the shift operation are zero-filled for unsigned quantities. For signed quantities, the sign bit is propagated into the vacated bit positions. The shift is a logical shift if the left operand is an unsigned quantity; otherwise, it is an arithmetic shift.

Microsoft Specific

The result of a right shift of a signed negative quantity is implementation-dependent. Although Microsoft C++ propagates the most-significant bit to fill vacated bit positions, there is no guarantee that other implementations will also do so.

// expre_Shift_Operators.cpp
// compile with: /EHsc
// Demonstrate shift operators
#include <iostream>
using namespace std;

int main() {
   cout   << "5 times 2 is " << (5 << 1) << endl
         << "20 divided by 4 is " << (20 >> 2) << endl;
}

Output

5 times 2 is 10
20 divided by 4 is 5

Date

History

Reason

May 2011

Showed the example output.

Information enhancement.

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