All I did was try to access a file with a self-made library. It didn't work. I tried again directly from the main file. This is the code:

File file = File("E:\\Users\\User\\Desktop\\dutils\\test.spr","r"); //This file exists on my system, so it should work...
file.close();

Output(Given to me by a message box that display's Throwable.msg in it's body):
Access Violation

Is this a bug, or me being stupid? If it's the latter, than tell me what went wrong. I am using DMD 2.097.2

On Wednesday, 18 August 2021 at 17:42:53 UTC, Ruby The Roobster wrote:

It's a bug in your code. "Access Violation" means your program tried to access out-of-bounds memory.

On Wednesday, 18 August 2021 at 17:54:47 UTC, Paul Backus wrote:

When I removed those two lines of code, the program ran perfectly without displaying any error or throwing any exception...

On Wednesday, 18 August 2021 at 17:54:47 UTC, Paul Backus wrote:

In addition, I figured out that if I moved the code outside of WndProc() everything worked fine, so I think it's a Win32 issue.

On Wednesday, 18 August 2021 at 17:42:53 UTC, Ruby The Roobster wrote:

File file = File("E:\\Users\\User\\Desktop\\dutils\\test.spr","r"); //This file exists on my system, so it should work...
file.close();

This is an error message you'll get from Windows if the file is locked (open by another application).

On Thursday, 19 August 2021 at 03:25:31 UTC, Jesse Phillips wrote:
tell me what went wrong. I am using DMD 2.097.2

case WM_CREATE: //Executed on creation of the window...
   try   {
      import core.stdc.stdio;
      FILE* file;
      file = fopen("file","r"); //NOTE: Replace 'file' with any file on the system...
      fclose(file);
   }
   catch(Throwable e)   {
      MessageBoxA(null,cast(const(char)*)e.msg,"ERROR",MB_OK | MB_ICONERROR);
   }

This works, no Message Box should be displayed(Note: use 2.097.2, this is the version I am using, and I don't know about if this same bug happens on earlier versions).

Now do this:

case WM_CREATE:
   try   {
      import std.stdio;
      File file = File("file","r");  //NOTE: Again, replace 'file' with any file on the system...
      file.close();
   }
   catch(Throwable e)   {
      MessageBoxA(null, cast(const(char)*)e.msg, "ERROR", MB_OK | MB_ICONERROR);
}

For me, this code generates the Message Box. Does this happen for you?

On Friday, 20 August 2021 at 04:27:34 UTC, Jesse Phillips wrote:

no errors
https://run.dlang.io/is/4tlm3p

void main() {
    try {
       import std.stdio: File;
       File file = File(__FILE__,"r");
       file.close();
   }
   catch(Throwable e) {
       import std.stdio: writefln;
       writefln("err=%s", e.msg);
   }
}

On Wednesday, 18 August 2021 at 17:56:53 UTC, Ruby The Roobster wrote:

The errors aren't always nicely located and can be elsewhere. Try to write a minimal runnable example. Also that cast won't work, you don't really know what you're doing there, use toStringz instead.

On Friday, 20 August 2021 at 05:22:20 UTC, nov wrote:

void main() {
    try {
       import std.stdio: File;
       File file = File(__FILE__,"r");
       file.close();
   }
   catch(Throwable e) {
       import std.stdio: writefln;
       writefln("err=%s", e.msg);
   }
}

This is not a console App. It's a Win32 one. Also, it turns out to be a bug. If I compile my application(with a couple of 'imports' removed under dmd 2.060), it works just fine, with no Access Violation Error. Try the following on dmd 2.060:

import core.runtime;

pragma(lib, "gdi32.lib");

import core.sys.windows.windows;
import std.stdio;

extern(Windows)
int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int iCmdShow)
{
    int result;

    try
    {
        Runtime.initialize();
        result = myWinMain(hInstance, hPrevInstance, lpCmdLine, iCmdShow);
        Runtime.terminate();
    }
    catch(Throwable o)
    {
        MessageBoxA(null, o.msg, "Error", MB_OK | MB_ICONERROR);
        result = 1;
    }

    return result;
}

int myWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int iCmdShow)
{
    HWND hwnd;
    MSG  msg;
    WNDCLASSA wndclass;

    wndclass.style         = CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc   = &WndProc;
    wndclass.cbClsExtra    = 0;
    wndclass.cbWndExtra    = 0;
    wndclass.hInstance     = hInstance;
    wndclass.hIcon         = LoadIconA(NULL, IDI_APPLICATION);
    wndclass.hCursor       = LoadCursorA(NULL, IDC_ARROW);
    wndclass.hbrBackground = cast(HBRUSH)GetStockObject(WHITE_BRUSH);
    wndclass.lpszMenuName  = NULL;
    wndclass.lpszClassName = appName.toUTF16z;

    if(!RegisterClassA(&wndclass))
    {

        return 0;
    }

    hwnd = CreateWindowA( "Test",
                         "Test",
                         WS_OVERLAPPEDWINDOW,
                         CW_USEDEFAULT,
                         CW_USEDEFAULT,
                         CW_USEDEFAULT,
                         CW_USEDEFAULT,
                         NULL,
                         NULL,
                         hInstance,
                         NULL);

    ShowWindow(hwnd, iCmdShow);
    UpdateWindow(hwnd);

    while (GetMessageA(&msg, NULL, 0, 0))
    {
        TranslateMessageA(&msg);
        DispatchMessage(&msg);
    }

    return msg.wParam;
}

extern(Windows)
LRESULT WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) nothrow
{
    switch (message)
    {
        case WM_CREATE:
            try
            {
               File file = File("test","r");
               file.close();
            }
            catch(Throwable e)
            {
               MessageBoxA(null, "Error", cast(char)[])e.msg,MB_OK | ICON_ERROR);
               PostQuitMessage(1);
            }
            return 0;
        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;

        default:
    }

    return DefWindowProcA(hwnd, message, wParam, lParam);
}

Sorry if I misnamed(forgot an 'A' at the end of the function name) something in above code.

Now, edit above code(provided that it has been fixed if necessary) by adding:

import core.sys.windows.wingdi;

And remove:

import core.sys.windows.windows;

And compile it with dmd 2.080.0 or later.

See the results(what matters is if you get the "Access Violation" error or not, everything else is irrelevant).