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std::basic_ios::operator bool – cppreference.com

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`operator void*() const;`	(1)	(bis C + +11)

`explicit operator bool() const;`	(2)	(seit C++11)

1)

Gibt eine Null-Zeiger, wenn fail() kehrt true, sonst gibt einen Nicht-Null-Zeiger. Dieser Zeiger ist implizit konvertierbar bool und kann in Booleschen Kontext verwendet werden .

Original:

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.

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2)

true kehrt, wenn der Stream hat keine Fehler aufgetreten sind und ist bereit von I / O-Operationen. Insbesondere kehrt !fail() .

Original:

Returns true if the stream has no errors occurred and is ready of I/O operations. Specifically, returns !fail().

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Dieser Operator ermöglicht es, Ströme und Funktionen, die Verweise zurück auf Streams als Loop Bedingungen, was in der idiomatischen C + + verwenden Input-Schleifen, wie while(stream >> value) {...} oder while(getline(stream, string)){...}. Solche Schleifen führen der Schleife Körper nur, wenn die Eingabe-Operation gelungen .

Original:

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.

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Parameter

(None)

Original:

(none)

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Rückgabewert

true wenn der Stream hat keine Fehler aufgetreten sind, false sonst .

Original:

true if the stream has no errors occurred, false otherwise.

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Beispiel

#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

Siehe auch

`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