C source ex01.c:

#include <stdio.h>
int main()
{
   printf("hello world\n");
   return 0;
}

'dmc ex01.c' produces message:

link ex01,,,user32+kernel32/noi;

but does generate .obj, .map and .exe files,
and the exe executes properly.

However, trying to use ImportC via 'dmd ex01.c' produces messages:

failed launching cl.exe /P /Zc:preprocessor /PD /nologo ex01.c /FIC:\D\dmd2\windows\bin64\..\..\src\druntime\import\importc.h /Fiex01.i
Error: C preprocess command cl.exe failed for file ex01.c, exit status 1

This behaviour was repeated after a complete fresh re-installation of dmd & dmc from the website.

On Wednesday, 19 April 2023 at 10:21:22 UTC, DLearner wrote:

#include <stdio.h>
int main()
{
   printf("hello world\n");
   return 0;
}

link ex01,,,user32+kernel32/noi;

failed launching cl.exe /P /Zc:preprocessor /PD /nologo ex01.c /FIC:\D\dmd2\windows\bin64\..\..\src\druntime\import\importc.h /Fiex01.i
Error: C preprocess command cl.exe failed for file ex01.c, exit status 1

Did you use the switch -m32omf?

https://dlang.org/spec/importc.html#auto-cpp

On Wednesday, 19 April 2023 at 11:50:28 UTC, bachmeier wrote:
[...]

No so following the references I tried every preprocessor option I could find:

C:\Users\SoftDev\Documents\BDM\D\ImportC>dmd ex01.c -m32omf
failed launching sppn.exe ex01.c -HIC:\D\dmd2\windows\bin64\..\..\src\druntime\import\importc.h -ED -oex01.i

Error: C preprocess command sppn.exe failed for file ex01.c, exit status 1


C:\Users\SoftDev\Documents\BDM\D\ImportC>dmd ex01.c -c -m32omf
failed launching sppn.exe ex01.c -HIC:\D\dmd2\windows\bin64\..\..\src\druntime\import\importc.h -ED -oex01.i

Error: C preprocess command sppn.exe failed for file ex01.c, exit status 1


C:\Users\SoftDev\Documents\BDM\D\ImportC>dmd ex01.c -c -m32mscoff
failed launching cl.exe /P /Zc:preprocessor /PD /nologo ex01.c /FIC:\D\dmd2\windows\bin64\..\..\src\druntime\import\importc.h /Fiex01.i
Error: C preprocess command cl.exe failed for file ex01.c, exit status 1


C:\Users\SoftDev\Documents\BDM\D\ImportC>dmd ex01.c -c -m64
failed launching cl.exe /P /Zc:preprocessor /PD /nologo ex01.c /FIC:\D\dmd2\windows\bin64\..\..\src\druntime\import\importc.h /Fiex01.i
Error: C preprocess command cl.exe failed for file ex01.c, exit status 1

Unfortunately all options failed.

On Wednesday, 19 April 2023 at 14:42:44 UTC, bachmeier wrote:
[...]

Well it took a little while, but I can confirm that if you have a D function like:

extern(C) void DCallee() {
   import core.stdc.stdio : printf;

   printf("Entered DCallee.\n");


   printf("Exiting DCallee.\n");
}

called from a C function like:

//  C Master calling D (under -betterC restrictions).

#include <stdio.h>

extern void DCallee();

int main()
{
   printf("MastC Entered.\n");

   DCallee();

   printf("MastC Exiting.\n");
   return 0;
}

Where the compilation is run from the batch file:

Rem Compile, link and run batch file.
IF EXIST .\DCallee.exe del .\DCallee.exe
IF EXIST .\DCallee.map del .\DCallee.map
IF EXIST .\DCallee.obj del .\DCallee.obj

IF EXIST .\MastC.exe del .\MastC.exe
IF EXIST .\MastC.map del .\MastC.map
IF EXIST .\MastC.obj del .\MastC.obj

dmd -m32omf -betterC -c DCallee.d

dmc MastC.c DCallee.obj
MastC.exe
Rem Exited compile, link and run batch file.

Then everything runs properly.

As an aside, it was a surprise to me to discover that the order of the file names in the
dmc line was significant, bearing in mind MastC.c contains a 'main' function, and DCallee.d does not.

As a further aside, I do recall the installer loading Visual Studio, but it didn't seem to help.