Re: Use C struct declaration without knowing definition
On Thursday, 25 July 2019 at 01:08:48 UTC, Ali Çehreli wrote:
And that type is traded as pointer to some_type on the C API,
right? Usually there is a factory method that returns a pointer
to a dynamically allocated object.
Correct, there is a function prototype that returns a dynamically
allocated instance of the struct.
Indeed. The only option is to use some_type* on the D API as
well:
extern(C) {
struct S;
S* C_API_allocate();
void C_API(const(S) *);
}
// D API
void foo(S* s) {
C_API(s);
}
void main() {
auto s = C_API_allocate();
foo(s);
}
This makes sense. I can only deal with pointers to dynamically
allocated instances of the struct since there is no way to know
the size of the struct at compile time. Now that I think about
it, this would be the case whether or not I was using D at all.
Thanks for your help!
Re: Use C struct declaration without knowing definition
On 07/24/2019 05:35 PM, Ben Ogles wrote:
> Is there a way to use a C header that contains a struct declaration but
> no definition?
>
> For example, the C header may contain:
>
> typedef struct some_type_s some_type;
>
> Which is only fully defined in the implementing C file:
>
> struct some_type_s { ... };
And that type is traded as pointer to some_type on the C API, right?
Usually there is a factory method that returns a pointer to a
dynamically allocated object.
> I am trying to wrap the header in D:
>
> extern(C)
> {
>struct some_type_s;
>alias some_type = some_type_s;
> }
>
> And then use it in another D file:
>
> some_type s;
>
> But dmd does not know the size of the struct so it can't compile. Is
> there a work around to this other than moving the struct definition into
> the C header file?
Indeed. The only option is to use some_type* on the D API as well:
extern(C) {
struct S;
S* C_API_allocate();
void C_API(const(S) *);
}
// D API
void foo(S* s) {
C_API(s);
}
void main() {
auto s = C_API_allocate();
foo(s);
}
Note: That program fails to link because C API functions are missing
definitions.
You can wrap the pointer i a D struct and dispatch member function calls
to the C API.
Ali
Use C struct declaration without knowing definition
Is there a way to use a C header that contains a struct
declaration but no definition?
For example, the C header may contain:
typedef struct some_type_s some_type;
Which is only fully defined in the implementing C file:
struct some_type_s { ... };
I am trying to wrap the header in D:
extern(C)
{
struct some_type_s;
alias some_type = some_type_s;
}
And then use it in another D file:
some_type s;
But dmd does not know the size of the struct so it can't compile.
Is there a work around to this other than moving the struct
definition into the C header file?
Re: Return the complete number
On Wednesday, 24 July 2019 at 16:16:15 UTC, Greatsam4sure wrote:
On Wednesday, 24 July 2019 at 15:57:06 UTC, a11e99z wrote:
On Wednesday, 24 July 2019 at 15:56:13 UTC, a11e99z wrote:
On Wednesday, 24 July 2019 at 15:45:08 UTC, Greatsam4sure
wrote:
int main(){
double mum = 0;
Write("enter a number: ")
readf(" %s\n",);
Writeln(num);
}
How do I return the complete number the user enter since I
don't since the user can enter numbers of various length
with dmd approximating it.
I will appreciate any help
readf!" %s\n"( num );
or
num.readf!" %s\n";
or
num = readln.strip.to!double;
writeln(num)
The result is always to six significant figure. I want the
whole number to be diaplay
So, there are several possible issues here. First, floating-point
numbers have limited precision - a double can not correctly
represent all integers above 2^52, for instance. That's 4.5
quadrillion though, so rarely an issue. In your case, as others
have commented, writefln with a correctly chosen format string[1]
will do the trick.
However, what is the correctly chosen format string? This is a
very hard question to answer, as it depends on what number was
typed, and what you mean by 'the complete number the user enter'.
While drug's suggestion of "%.16f" will return an accurate
representation of the floating-point number, it will include a
lot of trailing zeroes that were presumably not present in the
input string. It will also expose floating-point's limitations
when presented with huge numbers, like 1e23 will print
1603000.. The best option might
be "%.16g", which will choose the shortest of the scientific
notation and the regular notation, as well as strip trailing
zeroes. Depending on the criteria though, this might still not be
the optimal solution.
--
Simen
1: https://dlang.org/phobos/std_format.html#format-string
Re: How to contact people on the forum
On Wednesday, 24 July 2019 at 16:37:33 UTC, Greatsam4sure wrote: On Wednesday, 24 July 2019 at 15:56:43 UTC, drug wrote: 24.07.2019 18:51, Greatsam4sure пишет: Good day everyone. I am thinking, if there is a way to contact any person on dlang forums through mail or any other means. How do I get their email from their forum post? I use thunderbird to read the forum and every post contains email of its author, so I would use it to communicate. I don't use thunderbird any other options Email addresses are shown on the mailing list archive (and that's why I use a fake email address): http://lists.puremagic.com/pipermail/digitalmars-d/
Re: How to contact people on the forum
On Wednesday, 24 July 2019 at 16:37:33 UTC, Greatsam4sure wrote: On Wednesday, 24 July 2019 at 15:56:43 UTC, drug wrote: 24.07.2019 18:51, Greatsam4sure пишет: Good day everyone. I am thinking, if there is a way to contact any person on dlang forums through mail or any other means. How do I get their email from their forum post? I use thunderbird to read the forum and every post contains email of its author, so I would use it to communicate. I don't use thunderbird any other options On the web forum there”s a link labeled “Source” on every post. Click it to see the raw message, including the header which contains the email address. Just be aware that not everyone uses a valid email address.
Re: How to contact people on the forum
On Wednesday, 24 July 2019 at 15:56:43 UTC, drug wrote: 24.07.2019 18:51, Greatsam4sure пишет: Good day everyone. I am thinking, if there is a way to contact any person on dlang forums through mail or any other means. How do I get their email from their forum post? I use thunderbird to read the forum and every post contains email of its author, so I would use it to communicate. I don't use thunderbird any other options
Re: dip1000, perhaps annotate with return, and vibe-d
On Wednesday, 24 July 2019 at 12:54:51 UTC, aliak wrote:
Trying to get dip1000 flag in use. I have this error:
Error: returning Optional(null, false).this(value) escapes a
reference to parameter value, perhaps annotate with return
in this function:
public auto some(T)(auto ref T value) {
return Optional!T(value); // <-- error on this line
}
And it's instantiated from here:
static Optional!T fromRepresentation(Json value) {
if (value == Json.undefined) {
return no!T;
}
return some(deserializeJson!T(value)); // <-- instantiated
from here
}
I put the qualifier "return" on the parameter to some, but did
nothing. And I put it on Optional.this() as well, but I'm not
sure where I'm supposed to put it.
It should go on the constructor's parameter; i.e.,
this(auto return ref T value) { /* ... */ }
Under the hood, a constructor actually returns the constructed
value by reference, so the actual signature of the above
constructor seen by the lifetime checker is:
ref Optional!T __ctor(auto return ref T value)
You can see this for yourself with something like `pragma(msg,
typeof(Optional!T.__ctor))`.
Re: Return the complete number
On Wednesday, 24 July 2019 at 16:16:15 UTC, Greatsam4sure wrote: On Wednesday, 24 July 2019 at 15:57:06 UTC, a11e99z wrote: On Wednesday, 24 July 2019 at 15:56:13 UTC, a11e99z wrote: On Wednesday, 24 July 2019 at 15:45:08 UTC, Greatsam4sure The result is always to six significant figure. I want the whole number to be display see another answers at thread https://forum.dlang.org/post/qh9v10$19v1$1...@digitalmars.com https://forum.dlang.org/post/afzqnnorzwosimfqn...@forum.dlang.org
Re: Return the complete number
On Wednesday, 24 July 2019 at 15:57:06 UTC, a11e99z wrote:
On Wednesday, 24 July 2019 at 15:56:13 UTC, a11e99z wrote:
On Wednesday, 24 July 2019 at 15:45:08 UTC, Greatsam4sure
wrote:
int main(){
double mum = 0;
Write("enter a number: ")
readf(" %s\n",);
Writeln(num);
}
How do I return the complete number the user enter since I
don't since the user can enter numbers of various length with
dmd approximating it.
I will appreciate any help
readf!" %s\n"( num );
or
num.readf!" %s\n";
or
num = readln.strip.to!double;
writeln(num)
The result is always to six significant figure. I want the whole
number to be diaplay
oops! i misunderstood
Re: Return the complete number
On Wednesday, 24 July 2019 at 15:45:08 UTC, Greatsam4sure wrote:
int main(){
double mum = 0;
Write("enter a number: ")
readf(" %s\n",);
Writeln(num);
}
How do I return the complete number the user enter since I
don't since the user can enter numbers of various length with
dmd approximating it.
I will appreciate any help
as drug said: writefln with formatting
in case no need prints just string representation use
s/format https://dlang.org/phobos/std_format.html#format
auto str = num.format!"%.16s"; // using UFCS
or
auto str = "%.16s".format( num); // UFCS too for 2nd version of
format
or
string str = format( "%.16s", num);
simple help can be asked on IRC channel too
irc://irc.freenode.net/d
(HexChat, mIRC clients and others)
Re: Return the complete number
On Wednesday, 24 July 2019 at 15:56:13 UTC, a11e99z wrote:
On Wednesday, 24 July 2019 at 15:45:08 UTC, Greatsam4sure wrote:
int main(){
double mum = 0;
Write("enter a number: ")
readf(" %s\n",);
Writeln(num);
}
How do I return the complete number the user enter since I
don't since the user can enter numbers of various length with
dmd approximating it.
I will appreciate any help
readf!" %s\n"( num );
or
num.readf!" %s\n";
or
num = readln.strip.to!double;
oops! i misunderstood
Re: Return the complete number
On Wednesday, 24 July 2019 at 15:45:08 UTC, Greatsam4sure wrote:
int main(){
double mum = 0;
Write("enter a number: ")
readf(" %s\n",);
Writeln(num);
}
How do I return the complete number the user enter since I
don't since the user can enter numbers of various length with
dmd approximating it.
I will appreciate any help
readf!" %s\n"( num );
or
num.readf!" %s\n";
or
num = readln.strip.to!double;
Re: How to contact people on the forum
24.07.2019 18:51, Greatsam4sure пишет: Good day everyone. I am thinking, if there is a way to contact any person on dlang forums through mail or any other means. How do I get their email from their forum post? I use thunderbird to read the forum and every post contains email of its author, so I would use it to communicate.
Re: Return the complete number
24.07.2019 18:45, Greatsam4sure пишет:
int main(){
double mum = 0;
Write("enter a number: ")
readf(" %s\n",);
Writeln(num);
}
How do I return the complete number the user enter since I don't since
the user can enter numbers of various length with dmd approximating it.
I will appreciate any help
does it help?
writefln("%.8f", num); // for float
writefln("%.16f", num); // for double
How to contact people on the forum
Good day everyone. I am thinking, if there is a way to contact any person on dlang forums through mail or any other means. How do I get their email from their forum post?
Return the complete number
int main(){
double mum = 0;
Write("enter a number: ")
readf(" %s\n",);
Writeln(num);
}
How do I return the complete number the user enter since I don't
since the user can enter numbers of various length with dmd
approximating it.
I will appreciate any help
dip1000, perhaps annotate with return, and vibe-d
Trying to get dip1000 flag in use. I have this error:
Error: returning Optional(null, false).this(value) escapes a
reference to parameter value, perhaps annotate with return
in this function:
public auto some(T)(auto ref T value) {
return Optional!T(value); // <-- error on this line
}
And it's instantiated from here:
static Optional!T fromRepresentation(Json value) {
if (value == Json.undefined) {
return no!T;
}
return some(deserializeJson!T(value)); // <-- instantiated from
here
}
I put the qualifier "return" on the parameter to some, but did
nothing. And I put it on Optional.this() as well, but I'm not
sure where I'm supposed to put it.
The constructor for Optional takes an auto ref T ... I'm not sure
that makes sense. Does it make sense to take a constructor
parameter that is copied in to the struct by auto ref if you're
not calling .move on it explicitly?
And as for vibe-d, I get this when compiling with dip1000:
Also, vibe-d gives me this:
../../../.dub/packages/vibe-core-1.6.2/vibe-core/source/vibe/internal/traits.d(391,2): Error: static assert: "FileStream does not implement method "read" of type @safe ulong(scope ubyte[] dst, IOMode mode)"
Has anyone seen that or used vibed with dip1000?
