How to create dynamically sized objects
Nicholas Wilson via Digitalmars-d-learn
digitalmars-d-learn at puremagic.com
Thu Sep 29 19:28:02 PDT 2016
On Thursday, 29 September 2016 at 07:10:44 UTC, Straivers wrote:
> Hi,
>
> Say I wanted to create an object that has a string member, and
> I want the string to be allocated with the object contiguously
> instead of as a pointer to another location (as a constructor
> would do). For example:
>
> class C {
> this(int i, string s) {
> this.i = i;
> this.s = s.toUTF16z();
> }
>
> int i;
> wstring s;
> }
>
> I want to allocate memory such that it looks like this:
>
> [32-bit int][s.length * wchar.sizeof bytes]
>
> I've considered using a separate function to create the class,
> but I don't know how setting the length of the string would
> behave. The only solution I can think of would be to have a
> constructor like this:
>
> this(int i, string s, void[] mem) {
> emplace!int(mem.ptr, i);
>
> auto t = cast(dchar[]) mem[int.sizeof .. $];
> this.s.fill(s.byDChar())
> }
>
> Is there a better way to do this?
struct Foo
{
uint length;
wchar[0] str; //this is the equivalent of wchar_t[] in C. i.e
variable length.
}
auto newFoo(wstring s)
{
auto fooMem = new ubyte[ unit.sizeof +
wchar.sizeof*s.length];// you may need trailing '\0' if you are
trying to interoperate with C.
auto ret = cast(Foo*) fooMem;
ret.length = s.length;
memcpy(&ret.str,s.ptr, wchar.sizeof*s.length);
return ret;
}
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