C ++运算符意外错误

Question

I' m trying to define an operator for a class like this:

file.h

bool operator<<(XMLPair *p2);

file.cpp

bool XMLPair::operator<<(XMLPair *p2)
{
....
}

When I try to use it in the main program like this

XMLPair *p1, *p2 ;
...
p1<<p2

it says

error: invalid operands of types ‘XMLPair*’ and ‘XMLPair*’ to binary ‘operator<<’

Any idea?

Answer 1

p1 is a pointer; the left hand argument of a member operator has to be an object. So you need:

(*p1) << p2;

Although it would be more idiomatic for the right-hand argument to be a reference, and only to use pointers when you really need to:

// Remove `const` as necessary, if the operator needs to modify either operand
bool operator<<(XMLPair const & p2) const;

XMLPair p1, p2;
p1 << p2;

Answer 2

左侧必须是一个对象，而不是指针，请尝试：

(*p1) << p2;

Answer 3

You declared pointer to p1, and you call the operator on pointer. Try to invoke operator on (*p1), instead of p1.