Logical operators – cppreference.com

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Returns the result of a boolean operation.

Operator name	Syntax	Overloadable	Prototype examples (for `class T`)
Operator name	Syntax	Overloadable	Inside class definition	Outside class definition
negation	`not a` `!a`	Yes	`bool T::operator!() const;`	`bool operator!(const T &a);`
AND	`a and b` `a && b`	Yes	`bool T::operator&&(const T2 &b) const;`	`bool operator&&(const T &a, const T2 &b);`
inclusive OR	`a or b` `a \|\| b`	Yes	`bool T::operator\|\|(const T2 &b) const;`	`bool operator\|\|(const T &a, const T2 &b);`
'Notes' Original: Notes The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. The keyword-like forms (`and`,`or`,`not`) and the symbol-like forms (`&&`,`\|\|`,`!`) can be used interchangeably (See alternative Darstellungen) Alle eingebauten Operatoren Rückkehr `bool`, und die meisten benutzerdefinierten Überlastungen auch `bool` so dass die benutzerdefinierten Operatoren in der gleichen Weise wie die built-ins verwendet werden zurückkehren. Jedoch in einer benutzerdefinierten Operator Überlast kann jeder Typ als Rückkehr-Typ (einschließlich `void`) verwendet werden . Original: All built-in operators return `bool`, and most user-defined overloads also return `bool` so that the user-defined operators can be used in the same manner as the built-ins. However, in a user-defined operator overload, any type can be used as return type (including `void`). The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. Builtin operators `&&` and `\|\|` perform short-circuit evaluation (do not evaluate the second operand if the result is known after evaluating the first), but overloaded operators behave like regular function calls and always evaluate both operands

Erklärung

The logical operators apply logic functions (NOT, AND, and inclusive OR) to boolean arguments (or types contextually-convertible to bool), with a boolean result. Unlike the bitwise logic operators, these operators (in their built-in form) do not evaluate the second operand if the result is known after evaluating the first.

Builtin operators

The following built-in function signatures participate in overload resolution:


`bool operator!(bool)`

`bool operator&&(bool, bool)`

`bool operator\|\|(bool, bool)`

If the operand is not bool, it is converted to bool using contextual conversion to bool: it is only well-formed if the declaration bool t(arg) is well-formed, for some invented temporary t.

For the built-in logical NOT operator, the result is true if the operand is false. Otherwise, the result is false.

For the built-in logical AND operator, the result is true if both operands are true. Otherwise, the result is false. If the first operand is false, the second operand is not evaluated.

For the built-in logical OR operator, the result is true if either the first or the second operand (or both) is true. If the firstoperand is true, the second operand is not evaluated.

Results

`a`	`true`	`false`
`!a`	`false`	`true`

`and`		`a`
`and`		`true`	`false`
`b`	`true`	`true`	`false`
`b`	`false`	`false`	`false`

`or`		`a`
`or`		`true`	`false`
`b`	`true`	`true`	`true`
`b`	`false`	`true`	`false`

Beispiel

#include <iostream>
#include <string>
int main()
{
    int n = 2;
    int* p = &n;
    // pointers are convertible to bool
    if(    p && *p == 2   // "*p" is safe to use after "p &&"
       || !p &&  n != 2 ) // || has lower precedence than &&
        std::cout << "true\n";

    // streams are also convertible to bool
    std::cout << "Enter 'quit' to quit.\n";
    for(std::string line;    std::cout << "> "
                          && std::getline(std::cin, line)
                          && line != "quit"; )
        ;
}

Output:

true
Enter 'quit' to quit.
> test
> quit

Standard-Bibliothek

Because the short-circuiting properties of operator&& and operator|| do not apply to overloads, and because types with boolean semantics are uncommon, only two standard library classes overload these operators:


operator!	gilt eine unäre arithmetische Operator für jedes Element des valarray Original: applies a unary arithmetic operator to each element of the valarray The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (öffentliche Elementfunktion of `std::valarray`)

operator&& operator\|\|	gilt Binäroperatoren auf jedes Element von zwei valarrays oder ein valarray und einem Wert Original: applies binary operators to each element of two valarrays, or a valarray and a value The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (Funktions-Template)

operator!	prüft, ob ein Fehler aufgetreten ist (Synonym `fail()` ) Original: checks if an error has occurred (synonym of `fail()` ) The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (öffentliche Elementfunktion of `std::basic_ios`) [edit]

Siehe auch

Operator Vorrang

Common operators
Zuweisungen	incrementǊdecrement	Arithmetik	logisch	Vergleich	memberǊaccess	andererseits
`a = b a = rvalue a += b a -= b a *= b a /= b a %= b a &= b a \|= b a ^= b a <<= b a >>= b`	`++a --a a++ a--`	`+a -a a + b a - b a * b a / b a % b ~a a & b a \| b a ^ b a << b a >> b`	`!a a && b a \|\| b`	`a == b a != b a < b a > b a <= b a >= b`	`a[b] a &a a->b a.b a->b a.*b`	`a(...) a, b (type) a ? :`
Special operators
`static_cast` wandelt einem Typ in einen anderen kompatiblen Typ Original: `static_cast` converts one type to another compatible type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. `dynamic_cast` wandelt virtuellen Basisklasse abgeleitet class Original: `dynamic_cast` converts virtual base class to derived class The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. `const_cast` wandelt Typ kompatiblen Typ mit unterschiedlichen cv qualifiers Original: `const_cast` converts type to compatible type with different cv qualifiers The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. `reinterpret_cast` wandelt Typ inkompatibel type Original: `reinterpret_cast` converts type to incompatible type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. `new` ordnet memory Original: `new` allocates memory The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. `delete` freigibt memory Original: `delete` deallocates memory The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. `sizeof` fragt die Größe eines type Original: `sizeof` queries the size of a type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. `sizeof...` fragt die Größe eines Parameter Pack (seit C++11) Original: `sizeof...` queries the size of a Parameter Pack (seit C++11) The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. `typeid` fragt die Typinformationen eines type Original: `typeid` queries the type information of a type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. `noexcept` prüft, ob ein Ausdruck eine Ausnahme (seit C++11) werfen kann Original: `noexcept` checks if an expression can throw an exception (seit C++11) The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. `alignof` Abfragen Ausrichtungsanforderungen eines Typs (seit C++11) Original: `alignof` queries alignment requirements of a type (seit C++11) The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.