Thread: Is the book <<Thinking in C++>> Wrong?

  1. #1
    Registered User
    Join Date
    Apr 2007

    Is the book <<Thinking in C++>> Wrong?

    An example in the book Thinking in C++:

    class X{};
    X f() {
    	return X();
    void g1(X&){}
    void g2(const X&){}
    int main(){
    	return 0;
    According to the book the compiler should report error because f() returns a temporary object which is defined by the compiler as "const".
    However I compile this code using VS 2005 it works. Is the book wrong?


  2. #2
    Officially An Architect brewbuck's Avatar
    Join Date
    Mar 2007
    Portland, OR
    The book is not wrong. The compiler is wrong.

  3. #3
    C++ Witch laserlight's Avatar
    Join Date
    Oct 2003
    That is probably due to a too low warning level. I upped my warning level to /W4 and was informed:
    warning C4239: nonstandard extension used : 'argument' : conversion from 'X' to 'X &'
            A non-const reference may only be bound to an lvalue
    So what you see is nonstandard, and Thinking in C++ is correct.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  4. #4
    The larch
    Join Date
    May 2006
    VC++ seems to be kind of lax with constness of temporaries. In the current project I had some function prototypes like
    void foo(SomeObject&);
    And I called them like this:
    foo(SomeObject(x, y, x));
    MingW however requires SomeObject to be const in the function prototype for this to work.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

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