digitalmars.D.learn - Where can find fix length array memory layout document
- lili (5/5) Jun 18 2019 Hi guys:
- Daniel Kozak (8/13) Jun 18 2019 import std.stdio;
- Daniel Kozak (5/10) Jun 18 2019 When you do [1] without staticArray it will be automaticaly change to ar...
- Dennis (17/22) Jun 18 2019 I'm assuming you mean writeln([1].sizeof).
- lili (6/28) Jun 18 2019 Thanks a lot, where is a core.stdcpp.array , How to user it?
- XavierAP (33/38) Jun 20 2019 You are quite confused...
Hi guys:
Is the Dlang fix-length array alloc on stack? when a test
writeln([1]).sizeof //16
writeln([2]).sizeof //16
Why, What is the fix-length array memory layout.
Jun 18 2019
Daniel Kozak <kozzi11 gmail.com>
import std.stdio;
import std.array : staticArray;
void main() {
writeln([1].staticArray.sizeof); //4
writeln([2,5].staticArray.sizeof); //8
}
On Tue, Jun 18, 2019 at 2:30 PM lili via Digitalmars-d-learn <
digitalmars-d-learn puremagic.com> wrote:
Hi guys:
Is the Dlang fix-length array alloc on stack? when a test
writeln([1]).sizeof //16
writeln([2]).sizeof //16
Why, What is the fix-length array memory layout.
Jun 18 2019
On Tue, Jun 18, 2019 at 2:30 PM lili via Digitalmars-d-learn <
digitalmars-d-learn puremagic.com> wrote:
Hi guys:
Is the Dlang fix-length array alloc on stack? when a test
writeln([1]).sizeof //16
writeln([2]).sizeof //16
Why, What is the fix-length array memory layout.
When you do [1] without staticArray it will be automaticaly change to array
slice which consist of pointer to data (8bytes on 64bit) and length of
array again 8byte on 64bit
Jun 18 2019
On Tuesday, 18 June 2019 at 12:26:14 UTC, lili wrote:
Hi guys:
Is the Dlang fix-length array alloc on stack? when a test
writeln([1]).sizeof //16
writeln([2]).sizeof //16
Why, What is the fix-length array memory layout.
I'm assuming you mean writeln([1].sizeof).
An array literal is a slice of a dynamic array (which is length +
pointer, so 2*size_t size).
A fixed size array has to be declared as a local / member
variable, and then the content is on the stack:
```
int[10] a;
writeln(a.sizeof); // 40
writeln(a[].sizeof); // 16 on 64-bit or 8 on 32-bit
```
To get a static array literal, you can use the library function
staticArray:
```
import std.array;
writeln([1, 2, 3].staticArray.sizeof); // 12
```
Jun 18 2019
On Tuesday, 18 June 2019 at 12:39:45 UTC, Dennis wrote:On Tuesday, 18 June 2019 at 12:26:14 UTC, lili wrote:Thanks a lot, where is a core.stdcpp.array , How to user it? I test but get a error ``` auto aa = array!(int, 4); //error ```Hi guys: Is the Dlang fix-length array alloc on stack? when a test writeln([1]).sizeof //16 writeln([2]).sizeof //16 Why, What is the fix-length array memory layout.I'm assuming you mean writeln([1].sizeof). An array literal is a slice of a dynamic array (which is length + pointer, so 2*size_t size). A fixed size array has to be declared as a local / member variable, and then the content is on the stack: ``` int[10] a; writeln(a.sizeof); // 40 writeln(a[].sizeof); // 16 on 64-bit or 8 on 32-bit ``` To get a static array literal, you can use the library function staticArray: ``` import std.array; writeln([1, 2, 3].staticArray.sizeof); // 12 ```
Jun 18 2019
On Tuesday, 18 June 2019 at 13:05:03 UTC, lili wrote:On Tuesday, 18 June 2019 at 12:39:45 UTC, Dennis wrote:Please don't shorten your code or errors to the point where there's hardly any information left: it's hard to help you if we can't know what you did and what went wrong.On Tuesday, 18 June 2019 at 12:26:14 UTC, lili wrote:Thanks a lot, where is a core.stdcpp.array , How to user it? I test but get a error ``` auto aa = array!(int, 4); //error ```[...]I'm assuming you mean writeln([1].sizeof). An array literal is a slice of a dynamic array (which is length + pointer, so 2*size_t size). A fixed size array has to be declared as a local / member variable, and then the content is on the stack: ``` int[10] a; writeln(a.sizeof); // 40 writeln(a[].sizeof); // 16 on 64-bit or 8 on 32-bit ``` To get a static array literal, you can use the library function staticArray: ``` import std.array; writeln([1, 2, 3].staticArray.sizeof); // 12 ```
Jun 18 2019
On Tuesday, 18 June 2019 at 17:25:42 UTC, Cym13 wrote:On Tuesday, 18 June 2019 at 13:05:03 UTC, lili wrote:Forgot to say that it's probably because you don't actually build an array here, try adding parentheses: ``` auto aa = array!(int, 4)(); ```On Tuesday, 18 June 2019 at 12:39:45 UTC, Dennis wrote:Please don't shorten your code or errors to the point where there's hardly any information left: it's hard to help you if we can't know what you did and what went wrong.[...]Thanks a lot, where is a core.stdcpp.array , How to user it? I test but get a error ``` auto aa = array!(int, 4); //error ```
Jun 18 2019
On Tuesday, 18 June 2019 at 17:29:49 UTC, Cym13 wrote:On Tuesday, 18 June 2019 at 17:25:42 UTC, Cym13 wrote:array!(int,4)(); compile occurs a error say: no overload matches for arrayOn Tuesday, 18 June 2019 at 13:05:03 UTC, lili wrote:Forgot to say that it's probably because you don't actually build an array here, try adding parentheses: ``` auto aa = array!(int, 4)(); ```On Tuesday, 18 June 2019 at 12:39:45 UTC, Dennis wrote:Please don't shorten your code or errors to the point where there's hardly any information left: it's hard to help you if we can't know what you did and what went wrong.[...]Thanks a lot, where is a core.stdcpp.array , How to user it? I test but get a error ``` auto aa = array!(int, 4); //error ```
Jun 18 2019
On Wednesday, 19 June 2019 at 05:27:12 UTC, lili wrote:On Tuesday, 18 June 2019 at 17:29:49 UTC, Cym13 wrote:Did you import it properly? ``` void main() { import core.stdcpp.array; auto a = array!(int, 4)(); } ``` compiles and runs without issue for me. You'll have to show your code if you want people to help you there.On Tuesday, 18 June 2019 at 17:25:42 UTC, Cym13 wrote:array!(int,4)(); compile occurs a error say: no overload matches for arrayOn Tuesday, 18 June 2019 at 13:05:03 UTC, lili wrote:Forgot to say that it's probably because you don't actually build an array here, try adding parentheses: ``` auto aa = array!(int, 4)(); ```On Tuesday, 18 June 2019 at 12:39:45 UTC, Dennis wrote:Please don't shorten your code or errors to the point where there's hardly any information left: it's hard to help you if we can't know what you did and what went wrong.[...]Thanks a lot, where is a core.stdcpp.array , How to user it? I test but get a error ``` auto aa = array!(int, 4); //error ```
Jun 19 2019
On Wednesday, 19 June 2019 at 12:53:05 UTC, Cym13 wrote:
Did you import it properly?
```
void main() {
import core.stdcpp.array;
auto a = array!(int, 4)();
}
```
compiles and runs without issue for me. You'll have to show
your code if you want people to help you there.
Ok, where has some mistake in my code. thanks.
Jun 19 2019
On Tuesday, 18 June 2019 at 12:26:14 UTC, lili wrote:
Hi guys:
Is the Dlang fix-length array alloc on stack? when a test
writeln([1]).sizeof //16
writeln([2]).sizeof //16
Why, What is the fix-length array memory layout.
You are quite confused...
[...] is an array literal, not a static array. Those aren't the
same thing.
When you pass a array literal anywhere in your code, it will in
principle be referred as a slice variable. This will not
reallocate the contents. However the slice reference is another
variable that takes up two words of space (see code below).
This slice type is the same variable type that stores dynamic
arrays -- be they allocated or null.
Array literals are not necessarily allocated. The compiler is
free to embed them into the program machine code itself.
If you want a static array, you can just declare it directly e.g.
int[n] arr. Of course you can also generate is out of an array
literal with the staticArray std library function.
PS the layout of D arrays is of course linear and contiguous.
Both static or dynamic, just like C/C++ static arrays or
std::vectors respectively.
Hopefully this code makes things clear:
/*********/
enum lenInts = int.sizeof;
static assert(lenInts == 4);
int[1] arrStatic;
static assert(lenInts == arrStatic.sizeof);
auto slice = arrStatic[];
alias sliceType = typeof(slice);
static assert(is(sliceType == int[]));
enum lenPointers = size_t.sizeof; // fyi (unsinged) pointers
static assert(ptrdiff_t.sizeof == lenPointers); // fyi signed
pointer diff
static assert(sliceType.sizeof == 2 * lenPointers);
// because a D array reference remembers a pointer (like C) plus
the length (stored in a word-length integer)
Jun 20 2019