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From: Jonathan Wakely <jwakely.gcc@gmail.com>
Date: Tue, 28 Apr 2020 09:45:10 +0100
Message-ID: <CAH6eHdQSd1v8o4hSazRCjKmSZH9wJACH6dfadNJ7+8NPVQnLgw@mail.gmail.com>
Subject: Re: segment fault
To: luo alvin <alvinlmf@hotmail.com>
Cc: gcc-help <gcc-help@gcc.gnu.org>
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On Tue, 28 Apr 2020 at 07:07, luo alvin <alvinlmf@hotmail.com> wrote:
>
> Thank you very much for replying me. I also think it not bug,because I te=
st this code in the lower version(lower than 8.3.1-3) of gcc,all cause segm=
ent fault. The funny thing is that if you run this code higher than gcc ver=
sion(8.3.1-4)(actually I only test code in the version 8.3.1-4),the result =
is fine(doesn=E2=80=99t lead to segment fault).

Your program has undefined behaviour. That means anything can happen.

>furthermore, I found that the value of sizeof(std::string) is different be=
tween gcc versions. Value in version 8.3.1-3 is 8 ,and 32 in version 8.3.1-=
4.

That is not caused by the GCC version, it's caused by a different
default for the _GLIBCXX_USE_CXX11_ABI macro. When the default is 0
sizeof(std::string) =3D=3D sizeof(char*) but when the default is 1
sizeof(string) is larger.

See https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html
for more information about the macro.