Re: BetterC Name Mangling Linker Errors

[MyNameHere via Digitalmars-d-learn]

Thank you, that seems to have been the source of the error.

Re: BetterC Name Mangling Linker Errors

[Dennis via Digitalmars-d-learn]

On Wednesday, 27 July 2022 at 12:26:59 UTC, MyNameHere wrote:

```d
void Main(void* Instance)
{
WNDCLASSEXA WindowClass;
```


This is equivalent to `WNDCLASSEXA WindowClass = 
WNDCLASSEXA.init;`


If the struct's fields all initialize to 0, the compiler would 
simply set the variable's bytes to 0, but the definition in 
druntime gives fields with non-zero default value:


```D
struct WNDCLASSEXA {
UINT  cbSize = WNDCLASSEXA.sizeof; // <-- non zero init
UINT  style;
WNDPROC   lpfnWndProc;
int   cbClsExtra;
int   cbWndExtra;
HINSTANCE hInstance;
HICON hIcon;
HCURSOR   hCursor;
HBRUSHhbrBackground;
LPCSTRlpszMenuName;
LPCSTRlpszClassName;
HICON hIconSm;
}
```

Because of this, the compiler defines an 'init symbol' in 
druntime that gets copied into your variable to initialize it. 
Because druntime isn't linked when using BetterC, the linker 
fails to find the init symbol.


I think removing the default initialization will fix it:
```D
WNDCLASSEXA WindowClass = void;
```

BetterC Name Mangling Linker Errors

[MyNameHere via Digitalmars-d-learn]

I have included the source to a simple 64-bit Windows program.
It compiles and runs fine with ```dmd -m64 
-L="/Subsystem:Windows" -L="/Entry:Main" Main.d```. But compiling 
with ```-betterC``` using the following throws up a linker error, 
```dmd -m64 -betterC -L="/Subsystem:Windows" -L="/Entry:Main" 
Main.d```:


```Main.obj : error LNK2019: unresolved external symbol 
_D4core3sys7windows7winuser11WNDCLASSEXA6__initZ referenced in 
function Main```


And I'm not sure why.

```d
import core.sys.windows.winuser;
import core.sys.windows.winbase;

pragma(lib, "User32.lib");
pragma(lib, "Kernel32.lib");

extern(Windows)
void Main(void* Instance)
{
WNDCLASSEXA WindowClass;
with (WindowClass)
{
cbSize= WindowClass.sizeof;
lpfnWndProc   = 
hInstance = Instance;
hCursor   = LoadCursor(null, IDC_ARROW);
lpszClassName = "Window";
}
RegisterClassExA();
void *WindowHandle = CreateWindowExA(0,
 "Window",
 "Window",
 WS_OVERLAPPEDWINDOW,
 CW_USEDEFAULT,
 CW_USEDEFAULT,
 CW_USEDEFAULT,
 CW_USEDEFAULT,
 null,
 null,
 Instance,
 null);
ShowWindow(WindowHandle, SW_MAXIMIZE);

MSG Message;
while (GetMessage(, null, 0, 0))
{
TranslateMessage();
DispatchMessage();
}
}

extern(Windows)
long WindowProc(void* WindowHandle, uint Message, ulong WParam, 
long LParam) nothrow @system

{
if (Message == WM_DESTROY) ExitProcess(0);

return DefWindowProcA(WindowHandle, Message, WParam, LParam);
}
```