std::basic_ios::operator bool
From cppreference.com
| operator void*() const;
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(1) | (until C++11) |
| explicit operator bool() const;
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(2) | (since C++11) |
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 context.
2) Returns true if the stream has no errors occurred and is ready of 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.
Contents |
[edit] Parameters
(none)
[edit] Return value
true if the stream has no errors occurred, false otherwise.
[edit] Example
#include <iostream> #include <sstream> int main() { std::istringstream s("1 2 3 error"); int n; std::cout << std::boolalpha << "(bool)s is " << (bool)s << '\n'; while(s >> n) std::cout << n << '\n'; std::cout << std::boolalpha << "(bool)s is " << (bool)s << '\n'; }
Output:
(bool)s is true 1 2 3 (bool)s is false
[edit] See also
| checks if no error has occurred i.e. I/O operations are available (public member function) |
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| checks if a non-recoverable error has occurred (public member function) |
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| checks if a recoverable error has occurred (public member function) |
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| checks if end-of-file has been reached (public member function) |
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| checks if an error has occurred (synonym of fail()) (public member function) |
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