https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106248
Bug ID: 106248
Summary: operator>>std::basic_istream at boundary condition
behave differently in different opt levels
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: Ting.Wang.SH at ibm dot com
Target Milestone: ---
SYMPTOM:
Saw operator>>std::basic_istream set ios_base::eofbit differently when buffer
size equals to stream content size under different optimization levels. This is
observed on gcc version 11.2.0 with libstdc++.so.6.0.30, and not observed on
gcc version 9.4.0 with libstdc++.so.6.0.28.
This might not be a bug, however the behavior change under different
optimization levels is a little bit annoying.
An example C++ program is
$ cat a.cc
#include <istream>
#include <sstream>
#include <iostream>
char a_[10];
int main(int argc, char *argv[])
{
std::basic_string<char, std::char_traits<char>, std::allocator<char> >
input((const char *)" abcdefghi");
std::basic_stringbuf<char, std::char_traits<char>, std::allocator<char> >
sbuf(input);
std::basic_istream<char, std::char_traits<char> > istr(&sbuf);
istr >> a_;
std::cout << "istr.rdstate: " << istr.rdstate() << std::endl;
return 0;
}
$ g++ -O0 -o a.O0 a.cc
$ ./a.O0
istr.rdstate: 2
$ g++ -O3 -o a.O3 a.cc
$ ./a.O3
istr.rdstate: 0
