czw., 11 sty 2024 o 16:42 Arthur O'Dwyer via Std-Proposals
<std-proposals_at_[hidden]> napisał(a):
>
> On Thu, Jan 11, 2024 at 10:24 AM Andrey Semashev via Std-Proposals <std-proposals_at_[hidden]> wrote:
>>
>> On 1/11/24 17:42, Frederick Virchanza Gotham via Std-Proposals wrote:
>> > Today I wrote the following code; look at how I use a stack variable
>> > "exception_was_thrown":
>> >
>> > bool exception_was_thrown = false;
>> >
>> > try
>> > {
>> > Entry_Point_Thread_Terminal_Proper(str_comport);
>> > rs232win.Close(); // This is harmless no-op if the port isn't open
>> > }
>> > catch(std::exception const &e)
>> > {
>> > exception_was_thrown = true;
>> > LogText( std::string( "Exception (" ) + e.what() + ")" );
>> > }
>> > catch(...)
>> > {
>> > exception_was_thrown = true;
>> > LogText("Unknown Exception");
>> > }
>> >
>> > if ( exception_was_thrown )
>> > {
>> > pdialog->CallAfter(&Dialog_Main::CallTerminateFullRun);
>> > }
>> >
>> > Upon the catching of an exception, I want some common code to be
>> > executed for all of the 'catch' clauses.
>>
>> Why not use a scope guard?
>
>
> Right. You can do this pretty naturally using the `Auto` macro, for example:
> https://godbolt.org/z/b5zvKPb61
> The only trick is that the way to express "Do `OnTheWayOut` at the end of every catch-block" is really to express "Do an early exit at the end of the try block, and then let all the catch blocks fall through into `OnTheWayOut`." That's not as structured as we'd really like, but it's okay.
>
> void test(int x) {
> printf("Testing with x=%d\n", x);
> try {
> Auto(
> if (std::uncaught_exceptions() >= 1)


Was this incorrect when `test` is called inside of another `catch`?
At least for normal function (not coroutines) you should compare
```
if (old_uncaught_exceptions < std::uncaught_exceptions()) { /* do something */ }
```


> puts(" CallTerminateFullRun");
> );
> puts(" In try body");
> throw_if(x);
> puts(" Still in try body");
> return;
> } catch (const std::exception& ex) {
> printf(" Caught std::exception with message %s\n", ex.what());
> } catch (...) {
> puts(" Caught unknown exception");
> }
> puts(" OnTheWayOut");
> }
>
> Another, more structured, way to merge the catch blocks is to use a Lippincott function:
> https://godbolt.org/z/dfo797fao
> Here I've written it using P2927 `std::try_cast` as proposed for C++26 (note that I think there's a good chance we'll rename it to `std::exception_cast`), but you could do it by manually `rethrow_exception`'ing and `catch`ing just as well.
> (This is exactly what Ville just said, as I was in the process of typing this up.)
>
> void handle(std::exception_ptr p) {
> if (auto *ex = std::try_cast<std::exception>(p)) {
> printf(" Caught std::exception with message %s\n", ex->what());
> } else {
> puts(" Caught unknown exception");
> }
> }
>
> void test(int x) {
> printf("Testing with x=%d\n", x);
> try {
> puts(" In try body");
> throw_if(x);
> puts(" Still in try body");
> return;
> } catch (...) {
> puts(" CallTerminateFullRun");
> handle(std::current_exception());
> puts(" OnTheWayOut");
> }
> }
> --
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