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

std::basic_ios<CharT,Traits>::operatorbool: std::basic_ios<CharT,Traits>::operatorbool

NAME

std::basic_ios<CharT,Traits>::operatorbool - std::basic_ios<CharT,Traits>::operatorbool

Synopsis

operator void*() const; (1) (until C++11)
explicit operator bool() const; (2) (since C++11)

Checks whether the stream has no errors.
1) Returns a null pointer if fail() returns true, otherwise returns a non-null pointer. This pointer is implicitly convertible to bool and may be used in boolean contexts.
2) Returns true if the stream has no errors and is ready for I/O operations. Specifically, returns !fail().
This operator makes it possible to use streams and functions that return references to streams as loop conditions, resulting in the idiomatic C++ input loops such as while(stream >> value) {...} or while(getline(stream, string)){...}. Such loops execute the loop's body only if the input operation succeeded.

Parameters

(none)

Return value

true if the stream has no errors, false otherwise.

Example

// Run this code

  #include <iostream>
  #include <sstream>

  int main()
  {
      std::istringstream s("1 2 3 error");
      int n;
      std::cout << std::boolalpha << "s is " << static_cast<bool>(s) << '\n';
      while (s >> n) {
          std::cout << n << '\n';
      }
      std::cout << "s is " << static_cast<bool>(s) << '\n';
  }

Output:

  s is true
  1
  2
  3
  s is false