digitalmars.D.learn - What's best practice to use compound literals with structs and C-APIs?

=?iso-8859-1?Q?Robert_M._M=FCnch?= (12/12) May 01 2019 I use some C library that uses structs and many functions that use

Alex (11/20) May 01 2019 Look, even in C you have to workaround the case, where you want

=?iso-8859-1?Q?Robert_M._M=FCnch?= (17/40) May 01 2019 That would need me to change myfunc which is not possible because the D

Alex (11/32) May 01 2019 Found this bug:

=?iso-8859-1?Q?Robert_M._M=FCnch?= (16/35) May 02 2019 Thanks for the link, looks a bit related. I would need to see if I can

Alex (13/46) May 02 2019 For me, this works:

Jacob Carlborg (8/22) May 02 2019 struct A {...};

=?iso-8859-1?Q?Robert_M._M=FCnch?= <robert.muench saphirion.com> writes:

I use some C library that uses structs and many functions that use 
pointer to structs as arguments:

struct A {...};
myfunc(A *myA);

In C you can do this to get a lvalue:

myfunc(&(A){...});

In D this doesn't work and I get an "is not an lvalue and cannot be modified".

What's the correct D-ish way in such a case?

-- 
Robert M. M�nch
http://www.saphirion.com
smarter | better | faster

May 01 2019

Alex <sascha.orlov gmail.com> writes:

On Wednesday, 1 May 2019 at 12:47:22 UTC, Robert M. Münch wrote:
 I use some C library that uses structs and many functions that 
 use pointer to structs as arguments:

 struct A {...};
 myfunc(A *myA);

 In C you can do this to get a lvalue:

 myfunc(&(A){...});

 In D this doesn't work and I get an "is not an lvalue and 
 cannot be modified".

 What's the correct D-ish way in such a case?

Look, even in C you have to workaround the case, where you want 
to pass a value instead of a pointer. So, the proper question 
would be, how to redesign, so that &(A){...} is not needed.

However, to rebuild the same structure, auto ref parameters may 
be appropriate.
https://dlang.org/spec/template.html#auto-ref-parameters

or you new A(...) in place

or you use the byRef-pattern as shown in d-idioms
https://p0nce.github.io/d-idioms/#Rvalue-references:-Understanding-auto-ref-and-then-not-using-it

Not sure, which part is under your control...

May 01 2019

=?iso-8859-1?Q?Robert_M._M=FCnch?= <robert.muench saphirion.com> writes:

On 2019-05-01 14:23:37 +0000, Alex said:

 On Wednesday, 1 May 2019 at 12:47:22 UTC, Robert M. M�nch wrote:
 I use some C library that uses structs and many functions that use 
 pointer to structs as arguments:
 
 struct A {...};
 myfunc(A *myA);
 
 In C you can do this to get a lvalue:
 
 myfunc(&(A){...});
 
 In D this doesn't work and I get an "is not an lvalue and cannot be modified".
 
 What's the correct D-ish way in such a case?

 
 Look, even in C you have to workaround the case, where you want to pass 
 a value instead of a pointer.

That's not a workaround in C, it's the way to do it.

 However, to rebuild the same structure, auto ref parameters may be appropriate.
 https://dlang.org/spec/template.html#auto-ref-parameters

That would need me to change myfunc which is not possible because the D 
binding is all generated from C code.

 or you new A(...) in place

Doesn't work because this seems to kick in some D releated run-time 
stuff which lead to unresolved externals during linking:

error LNK2001: Nicht aufgel�stes externes Symbol "...__initZ".
error LNK2001: Nicht aufgel�stes externes Symbol 
"...__xtoHashFNbNeKxSQBtQBoQBfZm".
error LNK2001: Nicht aufgel�stes externes Symbol 
"...__xopEqualsFKxSQBsQBnQBeKxQmZb".

Not sure, why this happens.

 or you use the byRef-pattern as shown in d-idioms
 https://p0nce.github.io/d-idioms/#Rvalue-references:-Understanding-auto-ref-a
d-then-not-using-it 
 

This again would need my to change the C bindings, which are generated.

-- 
Robert M. M�nch
http://www.saphirion.com
smarter | better | faster

May 01 2019

Alex <sascha.orlov gmail.com> writes:

On Wednesday, 1 May 2019 at 14:59:48 UTC, Robert M. Münch wrote:
 On 2019-05-01 14:23:37 +0000, Alex said:

 However, to rebuild the same structure, auto ref parameters 
 may be appropriate.
 https://dlang.org/spec/template.html#auto-ref-parameters

 That would need me to change myfunc which is not possible 
 because the D binding is all generated from C code.

Ok, I see.

 or you new A(...) in place

 Doesn't work because this seems to kick in some D releated 
 run-time stuff which lead to unresolved externals during 
 linking:

 error LNK2001: Nicht aufgelöstes externes Symbol "...__initZ".
 error LNK2001: Nicht aufgelöstes externes Symbol 
 "...__xtoHashFNbNeKxSQBtQBoQBfZm".
 error LNK2001: Nicht aufgelöstes externes Symbol 
 "...__xopEqualsFKxSQBsQBnQBeKxQmZb".

 Not sure, why this happens.

Found this bug:
https://issues.dlang.org/show_bug.cgi?id=12374

It is closed now, because of inactivity, if you have a current 
case - a reopen is welcome.
However... Not sure, maybe someone else has more knowledge about 
this.

 or you use the byRef-pattern as shown in d-idioms
 https://p0nce.github.io/d-idioms/#Rvalue-references:-Understanding-auto-ref-and-then-not-using-it
 

 This again would need my to change the C bindings, which are 
 generated.

So, you generate D structs from C, right? If so, and if you need 
the byRef at any cost - you could tweak the generator, so byRef 
is generated for all structs.

May 01 2019

=?iso-8859-1?Q?Robert_M._M=FCnch?= <robert.muench saphirion.com> writes:

On 2019-05-01 19:13:54 +0000, Alex said:

 Doesn't work because this seems to kick in some D releated run-time 
 stuff which lead to unresolved externals during linking:
 
 error LNK2001: Nicht aufgel�stes externes Symbol "...__initZ".
 error LNK2001: Nicht aufgel�stes externes Symbol 
 "...__xtoHashFNbNeKxSQBtQBoQBfZm".
 error LNK2001: Nicht aufgel�stes externes Symbol 
 "...__xopEqualsFKxSQBsQBnQBeKxQmZb".
 
 Not sure, why this happens.

 
 Found this bug: https://issues.dlang.org/show_bug.cgi?id=12374
 
 It is closed now, because of inactivity, if you have a current case - a 
 reopen is welcome.
 However... Not sure, maybe someone else has more knowledge about this.

Thanks for the link, looks a bit related. I would need to see if I can 
create a small case which shows the problem...

 So, you generate D structs from C, right? If so, and if you need the 
 byRef at any cost - you could tweak the generator, so byRef is 
 generated for all structs.

Well, the generator is DStep... and I'm not sure if a general "byRef" 
approach would make sense. And listing affected structs manually will 
complicate the workflow again.

What I'm irriated about is, that this works:

A tmp = {x,y};
return myfunc(&tmp);

But this doesn't:

return myfunc(new A(x,y));

Or I haven't found a valid syntax to do it inline.

-- 
Robert M. M�nch
http://www.saphirion.com
smarter | better | faster

May 02 2019

Alex <sascha.orlov gmail.com> writes:

On Thursday, 2 May 2019 at 07:11:37 UTC, Robert M. Münch wrote:
 On 2019-05-01 19:13:54 +0000, Alex said:

 Doesn't work because this seems to kick in some D releated 
 run-time stuff which lead to unresolved externals during 
 linking:
 
 error LNK2001: Nicht aufgelöstes externes Symbol "...__initZ".
 error LNK2001: Nicht aufgelöstes externes Symbol 
 "...__xtoHashFNbNeKxSQBtQBoQBfZm".
 error LNK2001: Nicht aufgelöstes externes Symbol 
 "...__xopEqualsFKxSQBsQBnQBeKxQmZb".
 
 Not sure, why this happens.

 
 Found this bug: https://issues.dlang.org/show_bug.cgi?id=12374
 
 It is closed now, because of inactivity, if you have a current 
 case - a reopen is welcome.
 However... Not sure, maybe someone else has more knowledge 
 about this.

 Thanks for the link, looks a bit related. I would need to see 
 if I can create a small case which shows the problem...

 So, you generate D structs from C, right? If so, and if you 
 need the byRef at any cost - you could tweak the generator, so 
 byRef is generated for all structs.

 Well, the generator is DStep... and I'm not sure if a general 
 "byRef" approach would make sense. And listing affected structs 
 manually will complicate the workflow again.

yeah...

 What I'm irriated about is, that this works:

 A tmp = {x,y};
 return myfunc(&tmp);

 But this doesn't:

 return myfunc(new A(x,y));

 Or I haven't found a valid syntax to do it inline.

For me, this works:

´´´
void main()
{
     myfunc(new A(5));
}
struct A{
     int i;
}

void myfunc(A* myA){}
´´´

May 02 2019

Jacob Carlborg <doob me.com> writes:

On 2019-05-01 14:47, Robert M. Münch wrote:
 I use some C library that uses structs and many functions that use 
 pointer to structs as arguments:
 
 struct A {...};
 myfunc(A *myA);
 
 In C you can do this to get a lvalue:
 
 myfunc(&(A){...});
 
 In D this doesn't work and I get an "is not an lvalue and cannot be 
 modified".
 
 What's the correct D-ish way in such a case?

struct A {...};
myfunc(A *myA);

What about doing this:

auto a = A(/* set any values */);
myfunc(&a);

-- 
/Jacob Carlborg

May 02 2019

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digitalmars.D.learn - What's best practice to use compound literals with structs and C-APIs?