Condition checking: if(x==0) vs. if(!x)

Question

What\'s the differences of if(x==0) vs. if(!x)? Or are they always equivalent? And for different C++ build-in types of x:

Answer 1

if(!x)

is "if x is not false", that means that in order to evaluate that, you might have to cast x to a bool.

>> This can be harmful and if you wish to avoid it you should use something like the Safe Bool Idiom

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if(x!=0)

means "if x is not 0", so that is evaluated comparing x to 0. That might also involve an implicit conversion.

>> Be careful when using pointers this way, C++11 introduces a nullptr to avoid the confusion of NULL==0 (semantically different): What exactly is nullptr?