~~~char2.d
void main ()
{
   import std.stdio;
   import std.conv;
   char [2] win = [0, 'X'];
   auto ne = new Exception ("A " ~ win.to!string ~ " B");
   try throw ne;
   catch (Exception e)
      writeln ("exception caught: e.msg = <", e.msg, ">");
   throw ne;
}
~~~

Output:

exception caught: e.msg = <A X B>
object.Exception@char2.d(6): A              <--- truncated at \0
[...]

$ ./char2 | hexdump -c
0000000   e   x   c   e   p   t   i   o   n       c   a   u   g   h   t
0000010   :       e   .   m   s   g       =       <   A      \0   X
0000020   B   >  \n

$ ./char2 2>&1 1>/dev/null |hexdump -c
0000000   o   b   j   e   c   t   .   E   x   c   e   p   t   i   o   n
0000010   @   c   h   a   r   2   .   d   (   6   )   :       A      \n
0000020   -   -   -   -   -   -   -   -   -   -   -   -   -   -   -   -
[...]

Shall I file a bug?

On Sunday, 13 December 2020 at 11:51:19 UTC, kdevel wrote:
> ~~~char2.d
> void main ()
> {
>    import std.stdio;
>    import std.conv;
>    char [2] win = [0, 'X'];
>    auto ne = new Exception ("A " ~ win.to!string ~ " B");
>    try throw ne;
>    catch (Exception e)
>       writeln ("exception caught: e.msg = <", e.msg, ">");
>    throw ne;
> }
> ~~~
>
> [...]

Is it really a bug ? \0 truncates the string, as mentionned on this page :
https://en.wikipedia.org/wiki/Null-terminated_string

On Sunday, 13 December 2020 at 20:25:06 UTC, KapyoniK wrote:
> Is it really a bug ? \0 truncates the string, as mentionned on this page :
> https://en.wikipedia.org/wiki/Null-terminated_string

I thought the D runtime is written in D (with D strings)?!?

On 14/12/2020 9:56 AM, kdevel wrote:
> On Sunday, 13 December 2020 at 20:25:06 UTC, KapyoniK wrote:
>> Is it really a bug ? \0 truncates the string, as mentionned on this page :
>> https://en.wikipedia.org/wiki/Null-terminated_string
> 
> I thought the D runtime is written in D (with D strings)?!?

String literals are null terminated by the compiler. It is very useful for communicating with C.

On Sunday, 13 December 2020 at 20:58:42 UTC, rikki cattermole wrote:

[...]

> String literals are null terminated by the compiler. It is very useful for communicating with C.

Sure, but in the example given there is an embedded NUL which as part
of an exception msg. If caught everything works as expected, but if
the stack is unwound the information is lost due to truncation.

On Sunday, 13 December 2020 at 21:22:16 UTC, kdevel wrote:
> On Sunday, 13 December 2020 at 20:58:42 UTC, rikki cattermole wrote:
>
> [...]
>
>> String literals are null terminated by the compiler. It is very useful for communicating with C.
>
> Sure, but in the example given there is an embedded NUL which as part
> of an exception msg. If caught everything works as expected, but if
> the stack is unwound the information is lost due to truncation.

This is definitely a bug. The problem is that the D runtime uses `fprintf` to print the exception's error message, when it should be using `fwrite`:

https://github.com/dlang/druntime/blob/v2.094.2/src/rt/dmain2.d#L733

On Sunday, 13 December 2020 at 22:40:53 UTC, Paul Backus wrote:
> This is definitely a bug.

filed as Issue 21480