module user;

export { int myAddSeven(int a, int b); }

void main()
{
    int total = myAddSeven(2, 3);
}


>dmd -m64 -c user.d


module mydll;

export extern(D) {
    int myAddSeven(int a, int b) { return a+b+7; }  /* <-- function body */
}

>dmd -c -shared -m64  mydll.d

>link mydll.obj /DLL /NOENTRY
Microsoft (R) Incremental Linker Version 14.27.29111.0
Copyright (C) Microsoft Corporation.  All rights reserved.

   Creating library mydll.lib and object mydll.exp



>link user.obj /implib:mydll.lib
Microsoft (R) Incremental Linker Version 14.27.29111.0
Copyright (C) Microsoft Corporation.  All rights reserved.

LINK : fatal error LNK1104: cannot open file 'phobos64.lib'

or when I give the linker phobos64.lib

>link user.obj /implib:mydll.lib /LIBPATH:C:\D\dmd2\windows\lib64
Microsoft (R) Incremental Linker Version 14.27.29111.0
Copyright (C) Microsoft Corporation.  All rights reserved.

user.obj : error LNK2019: unresolved external symbol __imp__D4user10myAddSevenFiiZi referenced in function _Dmain
phobos64.lib(stacktrace_1be8_3e5.obj) : error LNK2019: unresolved external symbol snprintf referenced in function _D4core3sys7windows10stacktrace10StackTrace13resolveNoSyncFAxmZAAa
phobos64.lib(demangle_c96_79b.obj) : error LNK2001: unresolved external symbol snprintf
phobos64.lib(parseoptions_e2c_21b.obj) : error LNK2001: unresolved external symbol snprintf
phobos64.lib(parseoptions_e2c_21b.obj) : error LNK2019: unresolved external symbol sscanf referenced in function _D4core8internal12parseoptions5parseFNbNiAxaKANgaKfQkZb
user.exe : fatal error LNK1120: 3 unresolved externals

On Tuesday, 29 September 2020 at 21:22:21 UTC, WhatMeWorry wrote:
> module user;
>
> export { int myAddSeven(int a, int b); }
>
> [...]

it is better to use this template https://github.com/dlang/dmd/tree/master/samples/mydll

You don't have a DllMain.

On Wednesday, 30 September 2020 at 11:45:53 UTC, Ferhat Kurtulmuş wrote:
> On Tuesday, 29 September 2020 at 21:22:21 UTC, WhatMeWorry wrote:
>> module user;
>>
>> export { int myAddSeven(int a, int b); }
>>
>> [...]
>
> it is better to use this template https://github.com/dlang/dmd/tree/master/samples/mydll
>
> You don't have a DllMain.

yeah that's the problem, check [0] OP. The author makes commercial dll on windows so he knows what he speaks about

[0] https://forum.dlang.org/post/mscgsclxwtjcferfxoet@forum.dlang.org

On Tuesday, 29 September 2020 at 21:22:21 UTC, WhatMeWorry wrote:
> module user;
>
> export { int myAddSeven(int a, int b); }
>
> [...]

As example, DLL: https://github.com/vitalfadeev/dlang-dll

On Thursday, 1 October 2020 at 09:22:29 UTC, user1234 wrote:
> On Wednesday, 30 September 2020 at 11:45:53 UTC, Ferhat Kurtulmuş wrote:
>> On Tuesday, 29 September 2020 at 21:22:21 UTC, WhatMeWorry wrote:
>>> module user;
>>>
>>> export { int myAddSeven(int a, int b); }
>>>
>>> [...]
>>
>> it is better to use this template https://github.com/dlang/dmd/tree/master/samples/mydll
>>
>> You don't have a DllMain.
>
> yeah that's the problem, check [0] OP. The author makes commercial dll on windows so he knows what he speaks about
>
> [0] https://forum.dlang.org/post/mscgsclxwtjcferfxoet@forum.dlang.org

Yes, but shouldn't the /NOENTRY option take care of that. Say, I just want to make a DLL of simple functions.

On Thursday, 1 October 2020 at 20:03:19 UTC, WhatMeWorry wrote:
> Yes, but shouldn't the /NOENTRY option take care of that. Say, I just want to make a DLL of simple functions.

Your little example has 2 problems, the first being an incompatible extern(D) ex/import (mydll.myAddSeven vs. user.myAddSeven) and the second being an incomplete/wrong linker cmdline. When changing the myAddSeven declarations to extern(C++) (another option being a mydll.di header for the import), it works with

> dmd -m64 -shared -L/NOENTRY mydll.d
> dmd -m64 user.d mydll.lib

For more details, see also https://wiki.dlang.org/Win32_DLLs_in_D.

On Thursday, 1 October 2020 at 20:28:58 UTC, kinke wrote:
> On Thursday, 1 October 2020 at 20:03:19 UTC, WhatMeWorry wrote:
>> Yes, but shouldn't the /NOENTRY option take care of that. Say, I just want to make a DLL of simple functions.
>
> Your little example has 2 problems, the first being an incompatible extern(D) ex/import (mydll.myAddSeven vs. user.myAddSeven) and the second being an incomplete/wrong linker cmdline. When changing the myAddSeven declarations to extern(C++) (another option being a mydll.di header for the import), it works with
>
>> dmd -m64 -shared -L/NOENTRY mydll.d
>> dmd -m64 user.d mydll.lib
>
> For more details, see also https://wiki.dlang.org/Win32_DLLs_in_D.


Thanks all. I've gotten it to work with:

>dmd -m64 -ofmydll.dll  mydll.d  -L/NOENTRY -L/DLL

>dmd -m64 user.d mydll.lib

>user.exe
total = 12


But then I got cocky and decided to just added a writeln() in the mydll.d file and I've been fighting this link error ever since:

C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.27.29110\bin\Hostx64\x64\link.exe /NOLOGO "mydll.obj" /OUT:"mydll.dll"  /DEFAULTLIB:phobos64 /NOENTRY /DLL /OPT:NOICF  /LIBPATH:"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.27.29110\lib\x64" legacy_stdio_definitions.lib /LIBPATH:"C:\Program Files (x86)\Windows Kits\10\Lib\10.0.18362.0\ucrt\x64" /LIBPATH:"C:\Program Files (x86)\Windows Kits\10\lib\10.0.18362.0\um\x64"
   Creating library mydll.lib and object mydll.exp
mydll.obj : error LNK2019: unresolved external symbol fwrite referenced in function _D3std5stdio__T13trustedFwriteTaZQsFNbNiNePOS4core4stdcQBx6_iobufxAaZm
phobos64.lib(object_72_81a.obj) : error LNK2001: unresolved external symbol memcpy
phobos64.lib(exception_cf4_fff.obj) : error LNK2001: unresolved external symbol memcpy
phobos64.lib(bits_23fa_21c.obj) : error LNK2001: unresolved external symbol memcpy
phobos64.lib(gc_2413_a4e.obj) : error LNK2001: unresolved external symbol memcpy
phobos64.lib(gc_2415_a03.obj) : error LNK2001: unresolved external symbol memcpy
phobos64.lib(gc_2478_432.obj) : error LNK2001: unresolved external symbol memcpy
  o  o  o

On Thursday, 1 October 2020 at 21:35:42 UTC, WhatMeWorry wrote:
> On Thursday, 1 October 2020 at 20:28:58 UTC, kinke wrote:
>> [...]
>
>
> Thanks all. I've gotten it to work with:
>
>>[...]
>
>>[...]
>
>>[...]
> total = 12
>
> [...]

1) try running your commands in Visual Studio Native x64 CMD.
2) try link with msvcrt.lib

On Thursday, 1 October 2020 at 21:56:46 UTC, Ferhat Kurtulmuş wrote:
> On Thursday, 1 October 2020 at 21:35:42 UTC, WhatMeWorry wrote:
>> On Thursday, 1 October 2020 at 20:28:58 UTC, kinke wrote:
>>> [...]
>>
>>
>> Thanks all. I've gotten it to work with:
>>
>>>[...]
>>
>>>[...]
>>
>>>[...]
>> total = 12
>>
>> [...]
>
> 1) try running your commands in Visual Studio Native x64 CMD.

Yes, I've been doing that.

> 2) try link with msvcrt.lib

The only msvcrt.lib I can find on my Windows 10 machine is:

"C:\Windows Kits\10\Lib\10.0.19041.0\um\x64\ntstc_msvcrt.lib"

Also on Microsoft's docs
https://docs.microsoft.com/en-us/cpp/c-runtime-library/crt-library-features?view=vs-2019 it talks about a ucrt.lib?

On Friday, 2 October 2020 at 07:34:03 UTC, WhatMeWorry wrote:
> On Thursday, 1 October 2020 at 21:56:46 UTC, Ferhat Kurtulmuş wrote:
>> On Thursday, 1 October 2020 at 21:35:42 UTC, WhatMeWorry wrote:
>>> On Thursday, 1 October 2020 at 20:28:58 UTC, kinke wrote:
>>>> [...]
>>>
>>>
>>> Thanks all. I've gotten it to work with:
>>>
>>>>[...]
>>>
>>>>[...]
>>>
>>>>[...]
>>> total = 12
>>>
>>> [...]
>>
>> 1) try running your commands in Visual Studio Native x64 CMD.
>
> Yes, I've been doing that.
>
>> 2) try link with msvcrt.lib
>
> The only msvcrt.lib I can find on my Windows 10 machine is:
>
> "C:\Windows Kits\10\Lib\10.0.19041.0\um\x64\ntstc_msvcrt.lib"
>
> Also on Microsoft's docs
> https://docs.microsoft.com/en-us/cpp/c-runtime-library/crt-library-features?view=vs-2019 it talks about a ucrt.lib?

Here are the steps I used with success:

in a VCx64 cmd ->
set PATH=%PATH%;D:\dlang\dmd.2.094.0.windows\dmd2\windows\bin64
------------------------
module user;


import std.stdio;

import mydll; // Yes, I imported the dll here

//export { int myAddSeven(int a, int b); }

void main()
{
    int total = mydll.myAddSeven(2, 3);
    writeln(total);
}
-------------------------
module mydll;

export extern(D) {
    int myAddSeven(int a, int b) { return a+b+7; }  /* <-- function body */
}

---------------------------

dmd -m64 -ofmydll.dll  mydll.d  -L/NOENTRY -L/DLL
dmd -m64 user.d mydll.lib