int x[N]

[Gunnar G]

Hi.
Is the following code alright?

#include <iostream>
using namespace std;

int main(){
int N;
cin>>N;
int x[N];
cout<<x;
}

A friend told me this not alrigh, stack v.s. heap allocation, yada yada. We
are still arguing about this, so I turn to you, whom has more knowledge
about this. Is alright to do or not?
With GCC it is alright, not with visual studio.
What is your opinion on this?

[Alf P. Steinbach]

* Gunnar G:

Is the following code alright?

#include <iostream>
using namespace std;

int main(){
int N;
Don't use all-uppercase names except for macros, where you should use them.

cin>>N;
int x[N];
Supported in C99, not in C++: tell g++ to be conforming and it'll report an
error.

cout<<x;
Outputs the address of x.
}

--
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?

[Sumit Rajan]

"Gunnar G" <de****@comhem. se> wrote in message
news:E9******** *************@n ewsc.telia.net. ..

Hi.
Is the following code alright?

#include <iostream>
using namespace std;

int main(){
int N;
cin>>N;
Strictly speaking, this should not compile: int x[N];

Are you sure this(below) is what you want to do? cout<<x;

Regards,
Sumit.
--
Sumit Rajan <su****@msdc.hc ltech.com>

[Victor Bazarov]

Gunnar G wrote:

Is the following code alright?
Not in Standard C++.
#include <iostream>
using namespace std;

int main(){
int N;
cin>>N;
int x[N];
cout<<x;
}

A friend told me this not alrigh, stack v.s. heap allocation, yada yada. We
are still arguing about this, so I turn to you, whom has more knowledge
about this. Is alright to do or not?
With GCC it is alright, not with visual studio.
G++ (not GCC) has it as a language extension. VC++ doesn't.
What is your opinion on this?

My opinion is simple: do it if you don't care to be portable. If you know
that it's an extension and not a Standard C++ feature, and can understand
it when it stops compiling under another compiler, what's the big deal?

V

[Branimir Maksimovic]

"Gunnar G" <de****@comhem. se> wrote in message
news:E9******** *************@n ewsc.telia.net. ..

Hi.
Is the following code alright?
No.

#include <iostream>
using namespace std;

int main(){
int N;
cin>>N;
int x[N];
array size have to be constant expression, but
vector<int> x(N);
works ok
cout<<x;
}

A friend told me this not alrigh, stack v.s. heap allocation, yada yada.
We
are still arguing about this, so I turn to you, whom has more knowledge
about this. Is alright to do or not?
It's not alright, use vector.
With GCC it is alright, not with visual studio.
What is your opinion on this?

GCC imported everything that C99 has (and some more), into C++ . :)
Try compiling with -ansi for portable programs

Greetings, Bane.

[Gunnar G]

> Not in Standard C++.
Then I'll stay away from it for the sake of portability.
Thank you for your answers.

[Greg Comeau]

In article <E9************ *********@newsc .telia.net>,
Gunnar G <de****@comhem. se> wrote:

Is the following code alright?

#include <iostream>
using namespace std;

int main(){
int N;
cin>>N;
int x[N];
cout<<x;
}

A friend told me this not alrigh, stack v.s. heap allocation, yada yada. We
are still arguing about this, so I turn to you, whom has more knowledge
about this. Is alright to do or not?
With GCC it is alright, not with visual studio.
What is your opinion on this?

I don't have an opinion, but I know that Standard C++ doesn't
yet allow it. Intead you'll need maybe to use new int[M]
or vector<int>, with other appropriate changes as necessary.
If you compiler g++ with -Wall -ansi -pedantic you should get
more noise out of it.
--
Greg Comeau / Celebrating 20 years of Comeauity!
Comeau C/C++ ONLINE ==> http://www.comeaucomputing.com/tryitout
World Class Compilers: Breathtaking C++, Amazing C99, Fabulous C90.
Comeau C/C++ with Dinkumware's Libraries... Have you tried it?

[E. Robert Tisdale]

Gunnar G wrote:

Is the following code alright?

#include <iostream>
using namespace std;

int main(){
int N;
cin>>N;
int x[N];
cout<<x;
}

A friend told me this not alright, stack v.s. heap allocation, yada yada.
We are still arguing about this
so I turn to you, who have more knowledge about this.
Is it alright to do or not?
With GCC it is alright, not with visual studio.
What is your opinion on this? cat main.cc #include <iostream>

int main(int argc, char* argv[]) {
size_t n;
std::cin >> n;
int x[n];

for (size_t j = 0; j < n; ++j)
x[j] = j;
for (size_t j = 0; j < n; ++j)
std::cout << x[j] << std::endl;
return 0;
}
g++ -Wall -ansi -pedantic -o main main.cc main.cc: In function `int main(int, char**)':
main.cc:6: error: ISO C++ forbids variable-size array `x' ./main ./main: Command not found. g++ -Wall -o main main.cc
./main

3
0
1
2

The new C++ standard
will almost certainly adopt C99 variable-size arrays.
The GNU C++ compiler anticipates the new standard
and implements variable-sized arrays as an extension.
So they are certainly "alright"
and you certainly *should* use them
if you can be sure that every target platform will support them.