Casting a constant zero to a pointer type yields a null pointer. The conversion is done at compile time, so the compiler knows that a null pointer is the requir

Casting a constant zero to a pointer type yields a null pointer. The conversion is done at compile time, so the compiler knows that a null pointer is the required result. There is no requirement for an integer-to-pointer conversion to retain the bit pattern of the integer value, any more than an integer-to-floating-point conversion is required to do so. In most modern implementations, conversions among integer and pointer types of the same size are trivial, simply reinterpreting the bits as a value of a different type. A conforming C or C++ compiler can use, for example, the bit pattern 0xFFFFFFFF to represent a null pointer. Converting a constant 0 to a pointer type would yield a pointer with the representation 0xFFFFFFFF. Converting a non-constant 0 to a pointer type does not necessarily yield a null pointer; the result is implementation-defined, and may be indeterminate garbage.