[Bug c++/56032] New: Uniform initialization of references

[xazax.hun at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56032



 Bug #: 56032

   Summary: Uniform initialization of references

Classification: Unclassified

   Product: gcc

   Version: 4.7.1

Status: UNCONFIRMED

  Severity: major

  Priority: P3

 Component: c++

AssignedTo: unassig...@gcc.gnu.org

ReportedBy: xazax@gmail.com





Consider the following code:



//  CODE --



#include 

#include 





class S {

public:

S(const std::vector& v_) : v{v_} {}

void undefined() {

std::cout << v.front() << std::endl;

}

private:

const std::vector& v;

};



int main(){

std::vector foo {'f', 'a', 'i', 'l'};

std::cout << foo.front() << std::endl;

S s{foo};

s.undefined();



return 0;

}



//  END CODE --



Compiled with: g++ -std=c++11 main.cpp



s.undefined(); prints invalid characters or crashes the executable.



I think the result of the problem is that, the: v{v_}

initialization creates a new temporary from the vector that is destroyed after

the execution leaves the scope of the constructor. ( This would only be the

intended behaviour in case v would be initialized from initializer list, but

{v_} is clearly not an initializer list here.)



If I replace the uniform initialization with regular one: v(v_)

the snippet above works as intended.



The very same snippet does not compile with gcc 4.5.2. Slightly related report

on that issue: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50025.



I guess the origin of this problem is the incomplete fix of the error above.

[Bug c++/56032] Uniform initialization of references

[xazax.hun at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56032

--- Comment #1 from Gábor Horváth  2013-01-18 
15:01:45 UTC ---
(In reply to comment #0)
> Consider the following code:
> 
> //  CODE --
> 
> #include 
> #include 
> 
> 
> class S {
> public:
> S(const std::vector& v_) : v{v_} {}
> void undefined() {
> std::cout << v.front() << std::endl;
> }
> private:
> const std::vector& v;
> };
> 
> int main(){
> std::vector foo {'f', 'a', 'i', 'l'};
> std::cout << foo.front() << std::endl;
> S s{foo};
> s.undefined();
> 
> return 0;
> }
> 
> //  END CODE --
> 
> Compiled with: g++ -std=c++11 main.cpp
> 
> s.undefined(); prints invalid characters or crashes the executable.
> 
> I think the result of the problem is that, the: v{v_}
> initialization creates a new temporary from the vector that is destroyed after
> the execution leaves the scope of the constructor. ( This would only be the
> intended behaviour in case v would be initialized from initializer list, but
> {v_} is clearly not an initializer list here.)
> 
> If I replace the uniform initialization with regular one: v(v_)
> the snippet above works as intended.
> 
> The very same snippet does not compile with gcc 4.5.2. Slightly related report
> on that issue: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50025.
> 
> I guess the origin of this problem is the incomplete fix of the error above.

- I think the result of the problem is that, the: v{v_}
+ I think the source of the problem is that, the: v{v_}

[Bug c++/56032] Uniform initialization of references

[xazax.hun at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56032

--- Comment #3 from Gábor Horváth  2013-01-18 
15:39:08 UTC ---
(In reply to comment #2)
> (In reply to comment #0)
> > I guess the origin of this problem is the incomplete fix of the error above.
> 
> There is no fix, PR 50025 is still open and this is just a dup of it.

I added a new report because 50025 is about a compilation error, and with gcc
4.7 the code compiles, but fails to work as expected, but probably there issues
are closely related.

>
> N.B. the C++11 standard actually required this behaviour, but that's a defect
> that's been fixed in the latest draft.
> 

Could you point me to which part of the draft required this behaviour?

Thanks for your response,
Gábor