How to get error message when ifstream open fails

by

Every system call that fails update the errno value.

Thus, you can have more information about what happens when a ifstream open fails by using something like :

cerr << "Error: " << strerror(errno);

However, since every system call updates the global errno value, you may have issues in a multithreaded application, if another system call triggers an error between the execution of the f.open and use of errno.

On system with POSIX standard:

errno is thread-local; setting it in one thread does not affect its
value in any other thread.

Edit (thanks to Arne Mertz and other people in the comments):

e.what() seemed at first to be a more C++-idiomatically correct way of implementing this, however the string returned by this function is implementation-dependant and (at least in G++’s libstdc++) this string has no useful information about the reason behind the error…

More Related Contents:

  1. std::ofstream, check if file exists before writing
  2. Does my overload of operator
  3. Converting std::__cxx11::string to std::string
  4. Fastest way to check if a file exists using standard C++/C++11,14,17/C?
  5. Flattening iterator
  6. Why is the destructor of a future returned from `std::async` blocking?
  7. Append an int to a std::string [duplicate]
  8. C++ custom stream manipulator that changes next item on stream
  9. When using C headers in C++, should we use functions from std:: or the global namespace?
  10. declaring a priority_queue in c++ with a custom comparator
  11. What can and can’t I specialize in the std namespace?
  12. How to convert std::chrono::time_point to calendar datetime string with fractional seconds?
  13. How to read file content into istringstream?
  14. Is the C++ std::set thread-safe?
  15. Conversion function for error checking considered good?
  16. Can std::begin work with array parameters and if so, how?
  17. std::bind overload resolution
  18. Loop until integer input is in required range fails to work with non-digit character inputs
  19. std::ostringstream printing the address of the c-string instead of its content
  20. What is the difference between exit() and abort()?
  21. C++ Add months to chrono::system_clock::time_point
  22. Passing rvalues through std::bind
  23. Replace a line in text file
  24. error C2065: ‘cout’ : undeclared identifier
  25. Why does the C++ standard algorithm “count” return a difference_type instead of size_t?
  26. std::remove_const with const references
  27. Syntax for using std::greater when calling std::sort in C++
  28. C++ std::tuple order of destruction
  29. I want to kill a std::thread using its thread object? [duplicate]
  30. Getting an array of bytes out of Windows::Storage::Streams::IBuffer

Leave a Comment