new int?

[thomas]

#include<iostre am>
using namespace std;

int main(){
int *x = new int[10];
cout<<sizeof(x)/sizeof(int)<<en dl;
for(int i=0;i<20;i++) cout<<x[i]<<" ";
cout<<endl;
}

********output: ******
1
3670712 3670712 0 0 0 0 0 0 0 0 393219 524787 4301368 1 0 0 196610
524748 369016
8 3690232

while I expected:
10
??? error?

[Martin York]

Re: new int?

On Apr 9, 5:23 am, thomas <FreshTho...@gm ail.comwrote:

#include<iostre am>
using namespace std;
>
int main(){
int *x = new int[10];
cout<<sizeof(x)/sizeof(int)<<en dl;
for(int i=0;i<20;i++) cout<<x[i]<<" ";
cout<<endl;
>
}
>
********output: ******
1
3670712 3670712 0 0 0 0 0 0 0 0 393219 524787 4301368 1 0 0 196610
524748 369016
8 3690232
>
while I expected:
10
??? error?

sizeof(x) returns the sizeof(int*):
the number of bytes used by a pointer to int.
sizeof(int)
the number of bytes used by a int.

It looks like the size of the pointer is the same size of an int on
your system. What you wanted was the size of what x pointed at.
Unfortunately thats not possible via a pointer. What you may have
wanted to do was:

int main()
{
int x[10];
cout<<sizeof(x)/sizeof(int)<<en dl;
}

[Martin York]

Re: new int?

On Apr 9, 5:23 am, thomas <FreshTho...@gm ail.comwrote:

#include<iostre am>
using namespace std;
>
int main(){
int *x = new int[10];
cout<<sizeof(x)/sizeof(int)<<en dl;
for(int i=0;i<20;i++) cout<<x[i]<<" ";
cout<<endl;
>
}
>
********output: ******
1
3670712 3670712 0 0 0 0 0 0 0 0 393219 524787 4301368 1 0 0 196610
524748 369016
8 3690232
>
while I expected:
10
??? error?

Also note:
1) <emory allocated by new int[10] is un-initialized. ie it contains
random data. Hence the list of random numbers that you printed out.
2) Accessing beyond the end of the array is undefined behavior so
even though it managed to print out random numbers it is just as
likely to crash the program.
3) You should de-allocate the memory with delete [] x;

[Juha Nieminen]

Re: new int?

Martin York wrote:

3) You should de-allocate the memory with delete [] x;

Even better, you should avoid the 'new' altogether (if possible) and
use "std::vector<in tx(10);" instead.

[Jim Langston]

Re: new int?

"thomas" <FreshThomas@gm ail.comwrote in message
news:a97a6727-d185-4d5a-a9c9-5d2ca9719c4b@w4 g2000prd.google groups.com...

#include<iostre am>
using namespace std;
>
int main(){
int *x = new int[10];
cout<<sizeof(x)/sizeof(int)<<en dl;

What is x? x is an int*. What is the size of a pointer? On your system it
appears to be the size of an int (guessing 4). So this is outputting
cout << 4 / 4 << endl;

There is no way to know how much data a pointer is pointing to. You have to
store that value somewhere or get the information some other way.

for(int i=0;i<20;i++) cout<<x[i]<<" ";
cout<<endl;
}
>
********output: ******
1
3670712 3670712 0 0 0 0 0 0 0 0 393219 524787 4301368 1 0 0 196610
524748 369016
8 3690232
>
while I expected:
10
??? error?

--
Jim Langston
tazmaster@rocke tmail.com