Re: static array of pointers to dynamic arrays of ints problem...
On 4/22/18 2:00 AM, WhatMeForget wrote:
Surely a stupid mistake on my part, but why is the first array repeated?
In addition to what Neia said, you shouldn't use pointers to dynamic
arrays. Such things are really hard to allocate on the heap, since new
int[] just makes an array, not a pointer to an array. You're way more
likely to accidentally store pointers to stack variables (as demonstrated).
The only way 2 ways I know of to do it are to a) allocate a
multi-dimensional array, and take it's pointer (e.g. (new int[][1]).ptr)
or b) create a dummy struct with an array in it, and new that:
Struct Dummy { int[] array; }
auto p = new Dummy;
auto ptr =
Just use int[][2] a, you will be better off.
-Steve
Re: static array of pointers to dynamic arrays of ints problem...
On Sunday, 22 April 2018 at 06:00:15 UTC, WhatMeForget wrote:
foreach(i, elem; a)
{
int[] temp = new int[](5);
..
a[i] =
}
You're taking the address of a local variable and persisting it
beyond the variable's scope. This is not safe in general;
compilers regularly reuse spaces on the stack. DMD specifically
tends to do this reliably with foreach loop bodies.
You see the same thing in C:
#include
int main(int argc, char** argv)
{
int* p[2];
for (int i = 0; i < 2; i++)
{
int f = i;
p[i] =
}
printf("p[0] = %x, *p[0] = %d\n", p[0], *p[0]);
printf("p[1] = %x, *p[1] = %d\n", p[1], *p[1]);
return 0;
}
Which prints something like:
p[0] = d9b69428, *p[0] = 1
p[1] = d9b69428, *p[1] = 1
static array of pointers to dynamic arrays of ints problem...
Surely a stupid mistake on my part, but why is the first array
repeated?
import std.stdio;
void main()
{
int[]*[2] a; // a static arrray holding pointers to dynamic
arrays
static int unique = 0;
foreach(i, elem; a)
{
int[] temp = new int[](5);
foreach(ref element; temp)
{
element = unique;
unique++;
}
writeln("temp = ", temp);
a[i] =
}
foreach(i, elem; a)
{
writeln(a[i].length);
writeln("[", i, "][]", *a[i]);
}
}
temp = [0, 1, 2, 3, 4]
temp = [5, 6, 7, 8, 9]
5
[0][][5, 6, 7, 8, 9]
5
[1][][5, 6, 7, 8, 9]
