There are some important caveats, though, around trap or non-value representations. Basically, the value held by the storage for a variable may not correspond to a valid value of the variable's type.

For example, a bool variable usually takes a full byte but only has 2 valid representations in many ABIs (0 for false, 1 for true). That leaves 254 trap representations with 8-bit bytes, and trying to read any of these is undefined behavior.

Furthermore, a variable may be stored in a register (unless you take its address with &), and registers can store values wider than the variable type--e.g., even though int has no trap representations in memory of the same size, nowadays it's usually smaller than a register--or be in a state that makes them unreadable. Trying to read such a value is also undefined behavior.

So, reading memory in general is defined behavior (just with an indeterminate value) but it has to actually be memory and you have to be reading it into a type that can accept arbitrary bit patterns.