[PATCH] Fix PR libstdc++/19510: Uninitialized variable in some iterators

[Chris Jefferson]

Gabriel Dos Reis wrote:

>Chris Jefferson <caj@cs.york.ac.uk> writes:
>
>| Volker Reichelt wrote:
>| 
>| >PR libstdc++/19510 is about a warning that is triggered from within the
>| >libstdc++ headers. When compiling the following code snippet with
>| >"-Wall -O3" using mainline
>| >
>| >===============================================
>| >#include<vector>
>| >#include<list>
>| >
>| >std::vector<std::list<int>::iterator> v(1);
>| >===============================================
>| >
>| >the following warning is issued:
>| >
>| >/long_path/stl_construct.h: In function 'void
>| >__static_initialization_and_destruction_0(int, int)':
>| >/long_path/stl_construct.h:81: warning: 'SR.133' is used uninitialized in this
>| >function
>| >
>| >
>| I apologise if this is obvious / stupid, but is this really a bug in
>| the class, or in the error message?
>| 
>| I get the same error arriving from:
>| 
>| #include<vector>
>| 
>| struct ptrwrapper {
>| int* a;
>| ptrwrapper() {}
>| };
>| 
>| std::vector<ptrwrapper> v(1);
>
>
>That is an error in the class ptrwrapper.  Failing to initialise
>ptrwrapper::a results in undefined behaviour when you use it.
>  
>
But where am I "using" a? How this is this significantly different from 
the code:

int i=10;
int *a=&ci;
int* b;
a=b;

(or some such code)
which I believe is perfectly valid? (according to 8.3.1/2)