No Match For Operator+ ???????

This is a discussion on No Match For Operator+ ??????? within the C++ Programming forums, part of the General Programming Boards category; It still allows for implicit conversion such as const char* to std::string....

  1. #16
    C++まいる!Cをこわせ! Elysia's Avatar
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    It still allows for implicit conversion such as const char* to std::string.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  2. #17
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by Elysia View Post
    It still allows for implicit conversion such as const char* to std::string.
    I'm not sure what you mean. The reference has nothing to do with that. This works fine:

    Code:
    void do_something(std::string x)
    {
    }
    
    int main()
    {
        do_something("foo");
    }

  3. #18
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    >> It still allows for implicit conversion such as const char* to std::string.
    Perhaps you're thinking of how only some compilers allow conversion to non-const references (because you're binding a temporary to the non-const reference)?

  4. #19
    C++まいる!Cをこわせ! Elysia's Avatar
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    Yes, you're right. Only a non-const reference prohibits that kind of behaviour. Isn't it coming with C++0x, though?
    I always tend to pass via const reference unless it's a built-in type to ensure implicit construction and avoiding expensive copying.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  5. #20
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by Elysia View Post
    Yes, you're right. Only a non-const reference prohibits that kind of behaviour. Isn't it coming with C++0x, though?
    I'm not sure. The idea of a non-const reference binding to a temporary is inherently horrifying to me.

  6. #21
    C++まいる!Cをこわせ! Elysia's Avatar
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    Because of potential problems of modifying a temp object?
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  7. #22
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by Elysia View Post
    Because of potential problems of modifying a temp object?
    There's no conceptual problem with modifying a temporary, it's just pointless because... it's temporary.

    EDIT: Allowing a non-const reference to bind could also get in the way of a whole slew of possible optimizations.

    EDIT EDIT: Look up the "forwarding problem"
    Last edited by brewbuck; 05-14-2008 at 10:35 AM.

  8. #23
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    Note that at least one major compiler (I think gcc) allows this already.

  9. #24
    C++まいる!Cをこわせ! Elysia's Avatar
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    I know VS supports binding non-const default arguments to a reference.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  10. #25
    Cat without Hat CornedBee's Avatar
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    What's coming in C++0x is rvalue references, a new type of reference (the current one will be renamed lvalue reference) that can bind to temporaries, and that actually needs special measures to bind to non-temporaries.

    Because of this, you can then rely on the idea that nobody cares what happens to the referenced object. You can steal its state. That's the main idea behind move semantics. (A sane version of what auto_ptr's special copy constructor does.)
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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