operator void*() const; | (1) | (until C++11) |
explicit operator bool() const; | (2) | (since C++11) |
Checks whether the stream has no errors.
fail()
returns true
, otherwise returns a non-null pointer. This pointer is implicitly convertible to bool
and may be used in boolean contexts.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.
(none).
true
if the stream has no errors, false
otherwise.
#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
The following table shows the value of basic_ios
accessors (good()
, fail()
, etc.) for all possible combinations of ios_base::iostate
flags:
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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