Is it safe to check if a pointer is null, then dereference it in the same if statement?

Question

Is the following code safe if a null pointer is passed in?

if(ptr && *ptr == value)
{
   //do something
}

Does the order of the checks

Answer 1

In addition to all the others answers about ptr && *ptr == value being valid, but not the other way round, the notion of valid pointer may have different meaning.

The ptr could be an uninitialized variable, or could be obtained (e.g. by a cast from some random intptr_t integer) in such a way that it does not point anywhere (e.g. a dangling pointer) but is not null.

In that case, neither order of testing works.

Some pointers can be invalid and be non-null (then testing ptr && *ptr == value is undefined behavior). There is no portable way to test them. (but you could use operating-system or processor specific tricks).