std::basic_ios<CharT,Traits>::operator! (3) - Linux Manuals

std::basic_ios<CharT,Traits>::operator!: std::basic_ios<CharT,Traits>::operator!

NAME

std::basic_ios<CharT,Traits>::operator! - std::basic_ios<CharT,Traits>::operator!

Synopsis

bool operator!() const;

Returns true if an error has occurred on the associated stream. Specifically, returns true if badbit or failbit is set in rdstate().

Parameters

(none)

Return value

true if an error has occurred, false otherwise.

Example

// Run this code

  #include <iostream>
  #include <fstream>
  #include <cstdlib>
  int main()
  {
      std::ifstream file("test.txt");
      if(!file) // operator! is used here
      {
          std::cout << "File opening failed\n";
          return EXIT_FAILURE;
      }

      // typical C++ I/O loop uses the return value of the I/O function
      // as the loop controlling condition, operator bool() is used here
      for(int n; file >> n; ) {
         std::cout << n << ' ';
      }
      std::cout << '\n';

      if (file.bad())
          std::cout << "I/O error while reading\n";
      else if (file.eof())
          std::cout << "End of file reached successfully\n";
      else if (file.fail())
          std::cout << "Non-integer data encountered\n";
  }