I have function that returns pointer to child object.
Function prototype:
ObjClass* ObjClass::getChildFromParent(ObjClass* parent = nullptr);
This function has default parameter as null pointer and I want to check this parameter anyway, because if pointer is null I will return nullptr but if it's not I will return pointer to child object, so:
ObjClass* ObjClass::getChildFromParent(ObjClass* parent)
{
return parent == 0 ? nullptr : parent->getChild();
}
But I think checking null pointer using zero is not correct. So, should I use keyword to determine null pointer?
According to the C++ 14 Standard (5.10 Equality operators)
2 If at least one of the operands is a pointer, pointer conversions (4.10) and qualification conversions (4.4) are performed on both operands to bring them to their composite pointer type (Clause 5). Comparing pointers is defined as follows: Two pointers compare equal if they are both null, both point to the same function, or both represent the same address (3.9.2), otherwise they compare unequal.
And (4.10 Pointer conversions)
1 A null pointer constant is an integer literal (2.13.2) with value zero or a prvalue of type std::nullptr_t. A null pointer constant can be converted to a pointer type; the result is the null pointer value of that type and is distinguishable from every other value of object pointer or function pointer type. Such a conversion is called a null pointer conversion...
Thus the expression in the return statement
return parent == 0 ? nullptr : parent->getChild();
is entirely correct because the null pointer constant 0 is converted to a null pointer value of the type of the pointer parent. But it will be more expressive to write
return parent == nullptr ? nullptr : parent->getChild();