Yes. It is implementation-defined.
According to C++03 5.8/3 which defines right-shifting:
The value of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has
an unsigned type or if E1 has a signed type and a nonnegative value,
the value of the result is the integral part of the quotient of E1
divided by the quantity 2 raised to the power E2. If E1 has a signed
type and a negative value, the resulting value is
implementation-defined.
For more information, see this link.
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solved Is right shifting undefined behavior for negative number in cpp and in java?