Unexpected zero return code from `throw std::runtime_error`

[Csaba Raduly]

On Sat, 2 Jul 2022 at 15:22, Adam Dinwoodie  wrote:
>
> I'm currently experimenting with compiling rdfind for Cygwin, and one of
> the testcases is failing because std::runtime_error is expected to
> result in the compiled program exiting with a non-zero return code,
> but on Cygwin, it just seems to cause the program to terminate with a
> zero return code.
>
> I've attached a simple test case.  Compare the output on Cygwin...
>
>     $ ./test.sh
>     + cat
>     + g++ test.cc
>     + [[ -x a.exe ]]
>     + ./a.exe
>     + rc=0
>     + ((  rc == 0  ))
>     + echo 'Unexpected zero return code from execution'
>     Unexpected zero return code from execution
>     + exit 1
>
> ...with the output from one of my Debian boxes...
>
>     $ ./test.sh
>     + cat
>     + g++ test.cc
>     + [[ -x a.exe ]]
>     + [[ -x a.out ]]
>     + ./a.out
>     terminate called after throwing an instance of 'std::runtime_error'
>       what():  Test error
>     ./test.sh: line 21: 566327 Aborted                 ./a.out
>     + rc=134
>     + ((  rc == 0  ))
>     + echo 'Expected non-zero return code received: 134'
>     Expected non-zero return code received: 134
>     + exit 0
>
> I'm not massively familiar with C++, so I could well be missing
> something obvious, but this seems like an unexpected difference between
> Cygwin and other *nix platforms.  Is this a Cygwin bug, or am I doing
> something wrong?


Works just fine for me, unless I misunderstood something.

$ /cygdrive/c/Users/Csaba/Downloads/test.sh
+ cat
+ g++ test.cc
+ [[ -x a.exe ]]
+ ./a.exe
terminate called after throwing an instance of 'std::runtime_error'
  what():  Test error
/cygdrive/c/Users/Csaba/Downloads/test.sh: line 21:   641 Aborted
           (core dumped) ./a.exe
+ rc=134
+ ((  rc == 0  ))
+ echo 'Expected non-zero return code received: 134'
Expected non-zero return code received: 134
+ exit 0

The if goes in the "else" case because rc is not 0, as it should be.
(shoudn't the condition be $rc == 0 ?)
After

$ diff -u /cygdrive/c/Users/Csaba/Downloads/test.sh test.sh
--- /cygdrive/c/Users/Csaba/Downloads/test.sh   2022-07-02
22:09:21.506377100 +0200
+++ test.sh     2022-07-02 22:15:08.670809700 +0200
@@ -20,7 +20,8 @@
        exit 2
 fi

-if (( rc == 0 )); then
+if [[ $rc == 0 ]]
+then
        echo 'Unexpected zero return code from execution'
        exit 1
 else

I get

$ ./test.sh
+ cat
+ g++ test.cc
+ [[ -x a.exe ]]
+ ./a.exe
terminate called after throwing an instance of 'std::runtime_error'
  what():  Test error
./test.sh: line 21:   660 Aborted                 (core dumped) ./a.exe
+ rc=134
+ [[ 134 == 0 ]]
+ echo 'Expected non-zero return code received: 134'
Expected non-zero return code received: 134
+ exit 0


Csaba
-- 
You can get very substantial performance improvements
by not doing the right thing. - Scott Meyers, An Effective C++11/14 Sampler
So if you're looking for a completely portable, 100% standards-conformant way
to get the wrong information: this is what you want. - Scott Meyers (C++TDaWYK)