• Xiaochao Yan (30/31) Jun 07 Hi, I am new to D and is experimenting with game development
• Steven Schveighoffer (4/37) Jun 07 Put `printMessage` outside the main function. Inside the main
• Basile B. (19/25) Jun 08 on a recent compiler this should work:

Xiaochao Yan <leon_whbc yahoo.com> writes:

Hi, I am new to D and is experimenting with game development 
using D and C.

I had some problem when trying to recreate the
https://dlang.org/spec/importc.html

Environment:
Windows 11
gcc.exe (i686-posix-dwarf-rev0, Built by MinGW-W64 project) 8.1.0

Error Message:
```
lld-link: error: undefined symbol: _D4test4mainFZ12printMessageUZv
 referenced by test.obj:(_Dmain)



```

```
// .c file
#include <stdio.h>

void printMessage() {
     printf("Hello from C!\n");
}
```

```
// .d file
import std.stdio;
import std.conv;
import test;

void main() {

     writeln("Hello, World!");
     extern (C) void printMessage();
     printMessage();
}
```
Thanks in advance!

Steven Schveighoffer <schveiguy gmail.com> writes:

On Saturday, 8 June 2024 at 02:22:00 UTC, Xiaochao Yan wrote:
 Hi, I am new to D and is experimenting with game development 
 using D and C.

 I had some problem when trying to recreate the
 https://dlang.org/spec/importc.html

 Environment:
 Windows 11
 gcc.exe (i686-posix-dwarf-rev0, Built by MinGW-W64 project) 
 8.1.0

 Error Message:
 ```
 lld-link: error: undefined symbol: 
 _D4test4mainFZ12printMessageUZv
 referenced by test.obj:(_Dmain)



 ```

 ```
 // .c file
 #include <stdio.h>

 void printMessage() {
     printf("Hello from C!\n");
 }
 ```

 ```
 // .d file
 import std.stdio;
 import std.conv;
 import test;

 void main() {

     writeln("Hello, World!");
     extern (C) void printMessage();
     printMessage();
 }
 ```
 Thanks in advance!

Put `printMessage` outside the main function. Inside the main 
function, it has C linkage, but not C name mangling.

-Steve

Basile B. <b2.temp gmx.com> writes:

On Saturday, 8 June 2024 at 02:22:00 UTC, Xiaochao Yan wrote:
 Hi, I am new to D and is experimenting with game development 
 using D and C.

 I had some problem when trying to recreate the
 https://dlang.org/spec/importc.html

 [...]

 Thanks in advance!

on a recent compiler this should work:

```d
// .d file
import std.stdio;
import std.conv;
import test;

void main() {
     writeln("Hello, World!");

     pragma(mangle, "printMessage");
     extern (C) void printMessage();

     printMessage();
}
```

This was fixed by the dear GH Ghost in 
https://github.com/dlang/dmd/pull/15582.
A short technical explanation: mangling and call conventions are 
not 100% related.
You need to stuff the mangle for that to work.