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std::basic_ios::operator bool

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

#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

`ios_base::iostate` flags			`basic_ios` accessors
eofbit	failbit	badbit	`good()`	`fail()`	`bad()`	`eof()`	`operator bool`	`operator!`
false	false	false	true	false	false	false	true	false
false	false	true	false	true	true	false	false	true
false	true	false	false	true	false	false	false	true
false	true	true	false	true	true	false	false	true
true	false	false	false	false	false	true	true	false
true	false	true	false	true	true	true	false	true
true	true	false	false	true	false	true	false	true
true	true	true	false	true	true	true	false	true

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std::basic_ios::operator bool

Parameters

Return value

Example

See also