Is it not true that in either way the thread will get penalize for that check? In case if the check is done by container an undefined behavior could be avoided. 

On Mon, Oct 11, 2021, 1:18 PM Bo Persson via Std-Discussion <std-discussion@lists.isocpp.org> wrote:
On 2021-10-11 at 08:53, Anubhav Guleria via Std-Discussion wrote:
> Thanks for clarifying.
>
> Any specific reason why container's pop_back method can't check for
> current size and if it is 0 then make the pop operation a no-op?

That would be a cost that everyone would have to pay, even when you are
certain that the stack is never empty.

It is also extremely easy for user code to add the check, if and when
necessary:

if (!s.empty())
    s.pop();





>
> Thanks,
> Anubhav
>
> On Mon, Oct 11, 2021 at 6:17 AM Keenan Horrigan via Std-Discussion
> <std-discussion@lists.isocpp.org> wrote:
>>
>> This is expected as std::stack::pop calls the underlying container's pop_back method, and performing pop_back on an empty vector is undefined behavior.
>>
>> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
>>
>> On Sunday, October 10th, 2021 at 7:37 PM, Anubhav Guleria via Std-Discussion <std-discussion@lists.isocpp.org> wrote:
>>
>>> Hi,
>>>
>>> The following piece of code is giving Segmentation Fault.
>>>
>>> Probably the size is getting overflowed and the condition is not
>>>
>>> handled in implementation.
>>>
>>> Is this a known issue?
>>>
>>> #include<iostream>
>>>
>>> #include<stack>
>>>
>>> #include<vector>
>>>
>>> using namespace std;
>>>
>>> int main(){
>>>
>>> stack<int, vector<int>> s;
>>>
>>> s.pop();
>>>
>>> cout<<s.size()<<endl;
>>>
>>> if(!s.empty()){
>>>
>>> cout<<s.top()<<endl;
>>>
>>> }
>>>
>>> return 0;
>>>
>>> }
>>>
>>> I compiled with: g++ -std=c++17 test.cpp
>>>
>>> Output I got:
>>>
>>> 18446744073709551615
>>>
>>> Segmentation fault (core dumped)
>>>
>>> Output with -fsanitize=address flag
>>>
>>> g++ -std=c++17 -fsanitize=address test.cpp
>>>
>>> anubhav@turing:~/Documents/Programming$ ./a.out
>>>
>>> 18446744073709551615
>>>
>>> AddressSanitizer:DEADLYSIGNAL
>>> ===============================================================================================================================================================================================================================================================================================================================================================================================
>>>
>>> ==6143==ERROR: AddressSanitizer: SEGV on unknown address
>>>
>>> 0x000000000000 (pc 0x559da7fa34e2 bp 0x7ffdefc01bf0 sp 0x7ffdefc01b40
>>>
>>> T0)
>>>
>>> ==6143==The signal is caused by a READ memory access.
>>>
>>> ==6143==Hint: address points to the zero page.
>>>
>>> #0 0x559da7fa34e1 in main (/home/anubhav/Documents/Programming/a.out+0x14e1)
>>>
>>> #1 0x7ff37989b0b2 in __libc_start_main
>>>
>>> (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
>>>
>>> #2 0x559da7fa330d in _start
>>>
>>> (/home/anubhav/Documents/Programming/a.out+0x130d)
>>>
>>> AddressSanitizer can not provide additional info.
>>>
>>> SUMMARY: AddressSanitizer: SEGV
>>>
>>> (/home/anubhav/Documents/Programming/a.out+0x14e1) in main
>>>
>>> ==6143==ABORTING
>>>
>>> g++ Version:
>>>
>>> g++ (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
>>>
>>> Copyright (C) 2019 Free Software Foundation, Inc.
>>>
>>> This is free software; see the source for copying conditions. There is NO
>>>
>>> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>>>
>>> Operating System:
>>>
>>> lsb_release -a
>>>
>>> No LSB modules are available.
>>>
>>> Distributor ID: Ubuntu
>>>
>>> Description: Ubuntu 20.04.3 LTS
>>>
>>> Release: 20.04
>>>
>>> Codename: focal
>>>
>>> Kernel: Linux 5.11.0-37-generic
>>>
>>> Thanks,
>>>
>>> Anubhav
>>> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------


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