what's the scope of i ?

[Zeng Dinghao]

int main() {
for (int i=0; i<10; i++) {
cout << "dfdfd" << endl;
}
for (int i=0; i<10; i++) {
cout << "dfdfd" << endl;
}
}

when compiling it in Visual C++, i got an error.
but using g++, it is no problem.

Could anybody what's wrong?

[Alf P. Steinbach]

* Zeng Dinghao:

int main() {
for (int i=0; i<10; i++) {
cout << "dfdfd" << endl;
}
for (int i=0; i<10; i++) {
cout << "dfdfd" << endl;
}
}

when compiling it in Visual C++, i got an error.
but using g++, it is no problem.
That's because MSVC has (pre-standard) backwards compatibility
as default: you need to turn a bunch of compiler options to make
that compiler standard-conforming in various respects.

Could anybody what's wrong?

1) No '#include <iostream>'.
2) No 'using namespace std;'.
3) Stylewise, using 'i++' instead of '++i'.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Ioannis Vranos]

Zeng Dinghao wrote:

int main() {
for (int i=0; i<10; i++) {
cout << "dfdfd" << endl;
}
for (int i=0; i<10; i++) {
cout << "dfdfd" << endl;
}
}

when compiling it in Visual C++, i got an error.
but using g++, it is no problem.

Could anybody what's wrong?

Yes, the compiler is very old. Upgrade to VC++ 2003.

--
Ioannis Vranos

http://www23.brinkster.com/noicys

[Unforgiven]

"Ioannis Vranos" <iv*@guesswh.at.grad.com> wrote in message
news:1098002279.86140@athnrd02...

Zeng Dinghao wrote:

int main() {
for (int i=0; i<10; i++) {
cout << "dfdfd" << endl;
}
for (int i=0; i<10; i++) {
cout << "dfdfd" << endl;
}
}

when compiling it in Visual C++, i got an error.
but using g++, it is no problem.

Could anybody what's wrong?

Yes, the compiler is very old. Upgrade to VC++ 2003.

Which is available free (the compiler anyway, not the GUI), at
http://msdn.microsoft.com/visualc/vctoolkit2003/

Anyway, you'd still need to zet either /Za or /Zc:forScope to get
standards-compliant behaviour.

--
Unforgiven

[Ioannis Vranos]

Unforgiven wrote:

Which is available free (the compiler anyway, not the GUI), at
http://msdn.microsoft.com/visualc/vctoolkit2003/

Anyway, you'd still need to zet either /Za or /Zc:forScope to get
standards-compliant behaviour.

int main()
{
for(int i=0; i<10; ++i)
;

for(int i=0; i<10; ++i)
;
}
C:\c>cl temp.cpp
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 13.10.3077 for 80x86
Copyright (C) Microsoft Corporation 1984-2002. All rights reserved.

temp.cpp
Microsoft (R) Incremental Linker Version 7.10.3077
Copyright (C) Microsoft Corporation. All rights reserved.

/out:temp.exe
temp.obj

C:\c>

--
Ioannis Vranos

http://www23.brinkster.com/noicys

[Unforgiven]

"Ioannis Vranos" <iv*@guesswh.at.grad.com> wrote in message
news:1098008738.444962@athnrd02...

Unforgiven wrote:

Which is available free (the compiler anyway, not the GUI), at
http://msdn.microsoft.com/visualc/vctoolkit2003/

Anyway, you'd still need to zet either /Za or /Zc:forScope to get
standards-compliant behaviour.

int main()
{
for(int i=0; i<10; ++i)
;

i = 4; // Should cause error, i not in scope

for(int i=0; i<10; ++i)
;
}

G:\My Documents>cl test.cpp
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 13.10.3077 for 80x86
Copyright (C) Microsoft Corporation 1984-2002. All rights reserved.

test.cpp
Microsoft (R) Incremental Linker Version 7.10.3077
Copyright (C) Microsoft Corporation. All rights reserved.

/out:test.exe
test.obj

G:\My Documents>cl test.cpp /Zc:forScope
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 13.10.3077 for 80x86
Copyright (C) Microsoft Corporation 1984-2002. All rights reserved.

test.cpp
test.cpp(6) : error C2065: 'i' : undeclared identifier

G:\My Documents>cl test.cpp /Za
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 13.10.3077 for 80x86
Copyright (C) Microsoft Corporation 1984-2002. All rights reserved.

test.cpp
test.cpp(6) : error C2065: 'i' : undeclared identifier

--
Unforgiven

[Ioannis Vranos]

Unforgiven wrote:

"Ioannis Vranos" <iv*@guesswh.at.grad.com> wrote in message
news:1098008738.444962@athnrd02...

Unforgiven wrote:

Which is available free (the compiler anyway, not the GUI), at
http://msdn.microsoft.com/visualc/vctoolkit2003/

Anyway, you'd still need to zet either /Za or /Zc:forScope to get
standards-compliant behaviour.

int main()
{
for(int i=0; i<10; ++i)
;

i = 4; // Should cause error, i not in scope

for(int i=0; i<10; ++i)
;
}

G:\My Documents>cl test.cpp
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 13.10.3077 for 80x86
Copyright (C) Microsoft Corporation 1984-2002. All rights reserved.

test.cpp
Microsoft (R) Incremental Linker Version 7.10.3077
Copyright (C) Microsoft Corporation. All rights reserved.

/out:test.exe
test.obj

G:\My Documents>cl test.cpp /Zc:forScope
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 13.10.3077 for 80x86
Copyright (C) Microsoft Corporation 1984-2002. All rights reserved.

test.cpp
test.cpp(6) : error C2065: 'i' : undeclared identifier

G:\My Documents>cl test.cpp /Za
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 13.10.3077 for 80x86
Copyright (C) Microsoft Corporation 1984-2002. All rights reserved.

test.cpp
test.cpp(6) : error C2065: 'i' : undeclared identifier

Yes, the key is this:
/Ze enable extensions (default)

/Za disable extensions (implies /Op)


C:\c>cl /Za temp.cpp
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 13.10.3077 for 80x86
Copyright (C) Microsoft Corporation 1984-2002. All rights reserved.

temp.cpp
temp.cpp(6) : error C2065: 'i' : undeclared identifier

C:\c>
I guess in the default mode, the compiler auto-detects the old style
code and accepts it. For example the following does not produce any errors:

int main()
{
for(int i=0; i<10; ++i)
;

int i = 4;

for(int i=0; i<10; ++i)
;
}
However in the OP compiler it does, as even his simpler code with two
loops refused to compile.

--
Ioannis Vranos

http://www23.brinkster.com/noicys

[Unforgiven]

"Ioannis Vranos" <iv*@guesswh.at.grad.com> wrote in message
news:1098012253.879248@athnrd02...
<snip>

However in the OP compiler it does, as even his simpler code with two
loops refused to compile.

I know all that, but my point was that you need /Za or /Zc:forScope to get
standards-compliant behaviour in for-loop scope. Even if VC7.1 compiles the
OP's code without those options, it's still not standards-compliant
behaviour because 'i' is still visible outside of the loops.

The OP is obviously using VC6 or older, because those are the only versions
of VC that fail for his code. Nevertheless, even though VC7+ don't fail on
that code, their behaviour is still not fully standards-compliant *unless*
you specify one of those options. That is what I was trying to say. I wasn't
trying to refute the fact that VC7+ would fix the OPs situation.

VC8 is still the same btw. IMO it should be the reverse though,
standards-compliant behaviour by default and non-standards compliant
behaviour with an option. Maybe I'll file a suggestion on that.

--
Unforgiven

[Ioannis Vranos]

Unforgiven wrote:

I know all that, but my point was that you need /Za or /Zc:forScope to get
standards-compliant behaviour in for-loop scope. Even if VC7.1 compiles the
OP's code without those options, it's still not standards-compliant
behaviour because 'i' is still visible outside of the loops.

The OP is obviously using VC6 or older, because those are the only versions
of VC that fail for his code. Nevertheless, even though VC7+ don't fail on
that code, their behaviour is still not fully standards-compliant *unless*
you specify one of those options. That is what I was trying to say. I wasn't
trying to refute the fact that VC7+ would fix the OPs situation.

VC8 is still the same btw. IMO it should be the reverse though,
standards-compliant behaviour by default and non-standards compliant
behaviour with an option. Maybe I'll file a suggestion on that.

Well if you use /Za then you get strict standard compliant behaviour.
GCC also is about the same, the default enables various extensions and
-std=c++98 -pedantic-errors provides strict standard compliant behaviour.

Essentially all compiles enable extensions in their default mode so as
system-dependent code to be able to compile. Like __fastcall etc
keywords in Win32, etc.
The important thing with an ISO C++ compliant is to *compile* ISO C++
code in default mode, and VC++ 2003, GCC, BC++ etc do that.

--
Ioannis Vranos

http://www23.brinkster.com/noicys