Re: segment fault

Re: segment fault

[Jonathan Wakely]

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 test this code in the lower version(lower than 8.3.1-3) of gcc,all cause segment fault. The funny thing is that if you run this code higher than gcc version(8.3.1-4)(actually I only test code in the version 8.3.1-4),the result is fine(doesn’t 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 between 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) == 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.

回复: segment fault

[luo alvin]

Thank you very much ,you help me a lot!

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________________________________
发件人: Jonathan Wakely <jwakely.gcc@gmail.com>
发送时间: Tuesday, April 28, 2020 4:45:10 PM
收件人: luo alvin <alvinlmf@hotmail.com>
抄送: gcc-help <gcc-help@gcc.gnu.org>
主题: Re: segment fault

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 test this code in the lower version(lower than 8.3.1-3) of gcc,all cause segment fault. The funny thing is that if you run this code higher than gcc version(8.3.1-4)(actually I only test code in the version 8.3.1-4),the result is fine(doesn’t 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 between 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) == 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.