Bitwise operators include the complement operator ~, bitwise shift operators >> and <<, bitwise AND operator &, bitwise exclusive OR operator ^, bitwise inclusive OR operator | and compound assignment operators >>=, <<=, &=, ^= and |=. Bitwise operators should be used only with unsigned integer operands, as the results of bitwise operations on signed integers are implementation-defined (Annex G.3.5 [ISO/IEC 9899:1990]).
The C90 StandardC11 standard, section 6.35, paragraph 4 [ISO/IEC 9899:19902011], states:
Some operators (the unary operator ~ , and the binary operators <<, >>, &, ^, and |, collectively described as bitwise operators) shall have operands that have integral type. These operators return values that depend on the internal representations of integers, and thus have implementation-defined aspects for signed types.
FurtherFurthermore, the bitwise shift operator << for signed type is not defined in C90 subclause 6.3.7 [ISO/IEC 9899:1990].operators << and >> are undefined under many circumstances, and are implementation-defined for signed integers for more circumstances; see rule INT34-C. Do not shift an expression by a negative number of bits or by greater than or equal to the number of bits that exist in the operand for more information.
Implementation details
The Microsoft C compiler documentation says that:
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On-line GCC documentation about the implementation of some bitwise operations on signed integers says:
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