c++ - fstream operator >> ()sometime crash

Question

I met a crash when I try to read content from a plain file.

#5 0x0d0bef60 in std::__throw_ios_failure(char const*) () from /usr/lib/libstdc++.so.6
#6 0x0d0c2d38 in std::basic_filebuf<char, std::char_traits<char> >::underflow() () from /usr/lib/libstdc++.so.6
#7 0x0d075454 in std::istream::sentry::sentry(std::istream&, bool) () from /usr/lib/libstdc++.so.6
#8 0x0d077510 in std::basic_istream<char, std::char_traits<char> >& std::operator>><char, std::char_traits<char> >(std::basic_istream<char, std::char_traits<char> >&, char&) () from /usr/lib/libstdc++.so.6
#9 0x0fc638dc in GetOpenMode () at /home/nvbldr/workspace/working_dir/BaseServices/Utils/src/Misc_func.cpp:38

The code is below:

#define OPEN_ENABLED_FILE"/var/open_mode"

char isOpenMode = default_mode;
fstream openModeFile;
char buff[2];
memset(buff, 0, 2);
openModeFile.open(OPEN_ENABLED_FILE, ios::in);
if (!openModeFile)
{
    isOpenMode = non_open_mode;
}
else
{
    openModeFile>> buff[0]; // Seems this line crashed. 
    isOpenMode = buff[0] == '1' ? open_mode : non_open_mode; 
    openModeFile.close();
}

I cannot see why, this not always happen. We are doing some stress test for 20 hours, only happned in one stress test. Can anyone help give some advice, thanks.

question from:https://stackoverflow.com/questions/65912205/fstream-operator-sometime-crash

Answer 1

The code below should work. The only change was the removal of the index operator.

char default_mode = 'w';
char isOpenMode = default_mode;
std::fstream openModeFile;
char buff[20];
memset(buff, 0, 20);
openModeFile.open("./txt.txt", std::ios::in);
if (!openModeFile)
{
  return 0;
}
else
{
    openModeFile>> buff; // Seems this line crashed. 
    isOpenMode = buff[0] // Not sure what you intended so I left it out
    openModeFile.close();
}
    std::cout << buff;
}