llvm dev - Oct 2008 - [LLVMdev] MS C++ gives error C2371 on this code while (obviously) gcc compiles it fine

Taken from tools/llvmc2/CompilationGraph.cpp:
...
    for (typename C::const_iterator B = EdgesContainer.begin(),
           E = EdgesContainer.end(); B != E; ++B) {
      const Edge* E = B->getPtr();
...

MS C++ compiler (VS 2008) gives:
...
CompilationGraph.cpp
..\..\..\llvm\tools\llvmc2\CompilationGraph.cpp(58) : error C2371:
'E' : redefinition; different basic types
        ..\..\..\llvm\tools\llvmc2\CompilationGraph.cpp(57) : see
declaration of 'E'
...

While GCC compiles it fine. (I'm assuming it does, 'cause almost
everyone here uses gcc)

Changing the code to
...
    for (typename C::const_iterator B = EdgesContainer.begin(),
           End = EdgesContainer.end(); B != End; ++B) {
      const Edge* E = B->getPtr();
...
makes the code compilable by MS C++. But as a curiosity (and I really
don't know the answer because I can barely read C++): Which compiler
got it right?

gcc is correct. According to the ISO specification, the for-init-statement 
is supposed to inject any variable names into the same declarative scope as 
the condition of an equivalent restructuring of the loop in the form of a 
while statement, which in turn fronts the declaration to an extra scope that 
surrounds the /entire/ loop construct. VC++ seems to be scoping the 
variables as if they were /inside/ of the loop and not creating this extra 
scope. Frowny. -J

--------------------------------------------------
From: "Yanko" <yhdezalvarez at gmail.com>
Sent: Thursday, October 02, 2008 8:12 AM
To: <llvmdev at cs.uiuc.edu>
Subject: [LLVMdev] MS C++ gives error C2371 on this code while 
(obviously)gcc compiles it fine

...
> makes the code compilable by MS C++. But as a curiosity (and I really
> don't know the answer because I can barely read C++): Which compiler
> got it right?

On Thu, Oct 2, 2008 at 11:34 AM, Jay Freeman (saurik) <saurik at
saurik.com>wrote:
> gcc is correct. According to the ISO specification, the for-init-statement
> is supposed to inject any variable names into the same declarative scope as
> the condition of an equivalent restructuring of the loop in the form of a
> while statement, which in turn fronts the declaration to an extra scope
> that
> surrounds the /entire/ loop construct. VC++ seems to be scoping the
> variables as if they were /inside/ of the loop and not creating this extra
> scope. Frowny. -J
This can be changed in the project settings for a VC++ project.  I think it
was called something like "Enforce for loop conformance" or so...
This is something I always change though.
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Jay Freeman (saurik) wrote:
> gcc is correct. According to the ISO specification, the for-init-statement 
> is supposed to inject any variable names into the same declarative scope as
> the condition of an equivalent restructuring of the loop in the form of a 
> while statement, which in turn fronts the declaration to an extra scope
that
> surrounds the /entire/ loop construct. VC++ seems to be scoping the 
> variables as if they were /inside/ of the loop and not creating this extra 
> scope. Frowny. -J
>   
Actually, gcc is wrong and VC++ got it right.
 From the C++ standard, 6.4p3:
> A name introduced by a declaration in a condition (either introduced 
> by the type-specifier-seq or the declarator of the
> condition) is in scope from its point of declaration until the end of 
> the substatements controlled by the condition. If the
> name is re-declared in the outermost block of a substatement 
> controlled by the condition, the declaration that re-declares
> the name is ill-formed.
Which gives us:

while (int x=0) {
    int x=0;   // error: redeclaration, clashes with condition
}

Both gcc and VC++ emit a compilation error for the above.

Then the standard says this, 6.5.3p1:
> names declared in the for-init-statement are in the same 
> declarative-region as those declared in the condition
So names inside the 'for' loop clash with both the condition and the 
for-init-statement:

for (int x=0;;) {
    int x=0;   // error: redeclaration, clashes with for-init-statement
}

but gcc, incorrectly, does not emit a compilation error.

And while we are on the subject, gcc is also wrong on this one:

if (int x=0) {
    int x=0;   // error: redeclaration, but gcc does not emit any errors.
}


-Argiris
> --------------------------------------------------
> From: "Yanko" <yhdezalvarez at gmail.com>
> Sent: Thursday, October 02, 2008 8:12 AM
> To: <llvmdev at cs.uiuc.edu>
> Subject: [LLVMdev] MS C++ gives error C2371 on this code while 
> (obviously)gcc compiles it fine
>
> ...
>   
>> makes the code compilable by MS C++. But as a curiosity (and I really
>> don't know the answer because I can barely read C++): Which
compiler
>> got it right? 
>>     
>
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