Global Pointers

[fonz2591@gmail.com]

Hello..

Im trying to make a way to have a dynamic array....
I was doing a test with global pointers and the heap. Would someone
tell me thy this doesn't compile:

#include <iostream>
using namespace std;

void Test();

int * ptr;
ptr = new int [3];
main(){
int * ptr;
ptr = new int [3];
ptr[2] = 1;
Test();
cout << ptr[3] << endl;
return 0;
}

void Test(){
delete[] ptr;
int * ptr;
ptr = new int [4];
ptr[3] = 10;
}

I get the error:
Test.cpp:7: error: expected constructor, destructor, or type conversion
before '=' token


Thanks alot

[vietor.liu]

Re: Global Pointers

int * ptr;
ptr = new int [3];
this is a execute code,and the c++ compiler can't create initialize code for
this status

<fonz2591@gmail .com> ????
news:1132637450 .540630.277140@ f14g2000cwb.goo glegroups.com.. .[color=blue]
> Hello..
>
> Im trying to make a way to have a dynamic array....
> I was doing a test with global pointers and the heap. Would someone
> tell me thy this doesn't compile:
>
> #include <iostream>
> using namespace std;
>
> void Test();
>
> int * ptr;
> ptr = new int [3];
> main(){
> int * ptr;
> ptr = new int [3];
> ptr[2] = 1;
> Test();
> cout << ptr[3] << endl;
> return 0;
> }
>
> void Test(){
> delete[] ptr;
> int * ptr;
> ptr = new int [4];
> ptr[3] = 10;
> }
>
> I get the error:
> Test.cpp:7: error: expected constructor, destructor, or type conversion
> before '=' token
>
>
> Thanks alot
>[/color]

[fonz2591@gmail.com]

Re: Global Pointers

What can i do to fix it?
Are global pointers that use the heap possible?

Thanks

[Gianni Mariani]

Re: Global Pointers

fonz2591@gmail. com wrote:[color=blue]
> Hello..
>
> Im trying to make a way to have a dynamic array....
> I was doing a test with global pointers and the heap. Would someone
> tell me thy this doesn't compile:
>
> #include <iostream>
> using namespace std;
>
> void Test();
>
> int * ptr;
> ptr = new int [3];[/color]
// replace the two lines above with.
int * ptr( new int [3] );

// However, even better ,,,
#include <vector>
std::vector<int > ptr(3);
[color=blue]
> main(){
> int * ptr;
> ptr = new int [3];[/color]
^^^ what's this ? You're leaking the initialization time new int[3]
[color=blue]
> ptr[2] = 1;
> Test();
> cout << ptr[3] << endl;
> return 0;
> }
>
> void Test(){
> delete[] ptr;
> int * ptr;
> ptr = new int [4];
> ptr[3] = 10;
> }[/color]

// if you're using vector
void Test()
{
ptr.clear();
ptr.resize(4);
}
[color=blue]
>
> I get the error:
> Test.cpp:7: error: expected constructor, destructor, or type conversion
> before '=' token
>
>
> Thanks alot
>[/color]

[fonz2591@gmail.com]

Re: Global Pointers

Wow..
That worked...
Thanks alot!
Sry about that extra thing...
I was doing some tests, and forgot to delete them...
Thanks!

[John Harrison]

Re: Global Pointers

fonz2591@gmail. com wrote:[color=blue]
> Hello..
>
> Im trying to make a way to have a dynamic array....[/color]

You shouldn't use pointers and you shouldn't use globals.

One day you'll see the merit of this. On that day you'll be a better
programmer.

john

[Gianni Mariani]

Re: Global Pointers

John Harrison wrote:[color=blue]
> fonz2591@gmail. com wrote:
>[color=green]
>> Hello..
>>
>> Im trying to make a way to have a dynamic array....[/color]
>
>
> You shouldn't use pointers and you shouldn't use globals.[/color]

Ever ?
[color=blue]
>
> One day you'll see the merit of this. On that day you'll be a better
> programmer.
>
> john[/color]

[BobR]

Re: Global Pointers


Gianni Mariani wrote in message ...[color=blue]
>fonz2591@gmail .com wrote:[color=green]
>> Hello..
>> Im trying to make a way to have a dynamic array....
>> I was doing a test with global pointers and the heap. Would someone
>> tell me thy this doesn't compile:
>>
>> #include <iostream>
>> using namespace std;
>> void Test();
>>
>> int * ptr;
>> ptr = new int [3];[/color]
>// replace the two lines above with.
>int * ptr( new int [3] );
>
>// However, even better ,,,
>#include <vector>
>std::vector<in t> ptr(3);
>[/color]
// >> main(){
int main(){ // as already stated in other post(s).
[color=blue][color=green]
>> int * ptr;
>> ptr = new int [3];[/color]
>^^^ what's this ? You're leaking the initialization time new int[3]
>[color=green]
>> ptr[2] = 1;
>> Test();
>> cout << ptr[3] << endl;
>> return 0;
>> }
>>[/color][/color]

Add to Gianni's post:
[color=blue][color=green]
>> void Test(){
>> delete[] ptr;[/color][/color]
This deletes the array pointed to by the global 'ptr'. The global pointer is
still there, and can now be re-assigned to (it wasn't 'const').
[color=blue][color=green]
>> int * ptr;[/color][/color]
This is another 'error'(see next comment), you are (re)declaring a pointer
with the same name as the global one.
[color=blue][color=green]
>> ptr = new int [4];[/color][/color]
This assigns to the local you just declared, where you need '::ptr' here to
get to the global. When you leave this function, you have no pointer to the
memory you just allocated - a memory leak. Another vote *for* 'vector'.
[color=blue][color=green]
>> ptr[3] = 10;[/color][/color]

delete[] ptr; // for the local pointer.
return;[color=blue][color=green]
>> }[/color]
>
>// if you're using vector
>void Test(){
> ptr.clear();
> ptr.resize(4);
>}[/color]

Hope I got that right, corrections are welcome.
--
Bob R
POVrookie

[BobR]

Re: Global Pointers


John Harrison wrote in message ...[color=blue]
>fonz2591@gmail .com wrote:[color=green]
>> Hello..
>> Im trying to make a way to have a dynamic array....[/color]
>
>You shouldn't use pointers and you shouldn't use globals.
>
>One day you'll see the merit of this. On that day you'll be a better
>programmer.
>john[/color]

So, you are saying we should:

int main(){
#include <iostream>

class MyThing{ /* guts go here*/ };
MyThing TheThing;

return 0;
}

Is that going to work in all cases? (Any cases?)
<G>
--
Bob R
POVrookie

[Michiel.Salters@tomtom.com]

Re: Global Pointers


Gianni Mariani wrote:[color=blue]
> John Harrison wrote:[color=green]
> > fonz2591@gmail. com wrote:
> >[color=darkred]
> >> Hello..
> >>
> >> Im trying to make a way to have a dynamic array....[/color]
> >
> >
> > You shouldn't use pointers and you shouldn't use globals.[/color]
>
> Ever ?[/color]

In the context of the question: yes.
If you need a dynamic array, use an STL collection. If you need global
access via a single instance, don't create a global object but use a
singleton
or dedicated access functions. (i.e. MyClass GetFoo(int)/void
SetFoo(int,MyCl ass))

HTH,
Michiel Salters