ostream chaining, output order

Question

I have a function that takes an ostream reference as an argument, writes some data to the stream, and then returns a reference to that same stream, like so:

Answer 1

Hexadecimal Output

Before C++11, the class std::ostream has a conversion function to void*. Since your print function returns std::ostream&, when evaluating std::cout << print(...), the returned std::ostream lvalue will be implicitly converted to void* and then be outputted as a pointer value. This is why there is a hexadecimal output.

Since C++11, this conversion function is replaced by an explicit conversion function to bool, so trying to output an std::ostream object becomes ill-formed.

Evaluation Order

Before C++17, overloaded operator is considered a function call for analyzing evaluation order, and evaluation order of different arguments of a function call is unspecified. So it is not strange that the print function is evaluated firstly, which causes How are you? is outputted firstly.

Since C++17, the evaluation order of operands of operator << is strictly from left to right, and operands of overloaded operator share the same evaluation order as those of the bulit-in one (see more details here). So your program will always get the output (assume print returns something able to be outputted)

Hello, world! How are you?
something returned by print

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