null pointer in C++

Question

everyone, I have some question about C++, what do You actually prefer to use

int* var = 0;

if(!var)...//1)
or
if(var == 0)..//2)

what are the pros and cons? thanks in advance

Answer 1

I prefer if (!var), because then you cannot accidentally assign to var, and you do not have to pick between 0 and NULL.

Answer 2

I've always been taught to use if (!var), and it seems that all the idiomatic C(++) I've ever read follows this. This has a few nice semantics:

• There's no accidental assignment
• You're testing the existence of something (ie. if it's NULL). Hence, you can read the statement as "If var does not exist" or "If var is not set"
• Maps closely to what you'd idiomatically write if var was a boolean (bools aren't available in C, but people still mimic their use)
• Similar to the previous point, it maps closely to predicate function calls, ie. if (!isEmpty(nodeptr)) { .. }