Re: array of zero elements
- From: Abhishek Padmanabh <abhishek.padmanabh@xxxxxxxxx>
- Date: Sun, 17 Feb 2008 04:07:11 -0800 (PST)
On Feb 17, 3:26 pm, George <Geo...@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Hello everyone,
Sometimes, we allocate array of zero elements. I am wondering for what
regualr purpose will we do that?
It is valid so that you can have code like this:
void f(size_t n)
{
int * ptr = new int[n];
//...
delete[] ptr;
}
instead of:
void f(size_t n)
{
if (n>0)
{
int * ptr = new int[n];
//...
delete[] ptr;
}
}
No other use though, because since it has zero elements, you cannot do
anything with it.
That would not mean that there is no use of zero sized (or better say
'unsized') arrays. VC++ has an extension which makes use of zero sized
arrays as the last member of structures. For example, see this:
#include<cstdlib>
#include<iostream>
struct test
{
int cb;
int buf[];
};
int main()
{
test* bb;
int length = 10;
bb = (test*) malloc(sizeof(test)+sizeof(int)*length);
bb->cb = length;
//fill buf with length int items or can copy from another array for
length elements
bb->buf[i]=10; //i should be less than length
//OR--------
test aa = {10, {1,10,22,32}};
std::cout << aa.buf[2];
}
Since the zero size member is in there, there are few restrictions as
well. You cannot create an array of the test struct. You can mimic
that though like this:
//create an array of length 10 of test pointers
test * ptr[10];
//set each of the pointers to individual elements created as above
Generally, you would be better off keeping a pointer member but it is
worth noting the presence of such an extension. See for details :
http://msdn2.microsoft.com/en-us/library/ms858712.aspx
.
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