我可以在 C++ 中对 int 值使用 not 运算符吗？
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Can I use the not operator in C++ on int values?
提问by 001
Strange question, but someone showed me this, I was wondering can you use the not ! operator for int in C++? (its strange to me).
奇怪的问题，但有人给我看了这个，我想知道你能不能使用 not ！C++中int的运算符？（这对我来说很奇怪）。
#include <iostream>
using namespace std;
int main()
{
int a=5, b=4, c=4, d;
d = !( a > b && b <= c) || a > c && !b;
cout << d;
system ("pause");
return 0;
}
回答by kennytm
Yes. For integral types, !returns trueif the operand is zero, and falseotherwise.
是的。对于整数类型，如果操作数为零则!返回true，false否则返回。
So !bhere just means b == 0.
所以!b这里只是意味着b == 0.
This is a particular case where a value is converted to a bool. The !bcan be viewed as !((bool)b)so the question is what is the "truthness" of b. In C++, arithmetic types, pointer types and enum can be converted to bool. When the value is 0 or null, the result is false, otherwise it is true(C++ §4.1.2).
这是将值转换为 的特殊情况bool。该!b可被视为!((bool)b)这样的问题是什么的“truthness” b。在 C++ 中，算术类型、指针类型和枚举可以转换为bool. 当值为 0 或 null 时，结果为false，否则为true(C++ §4.1.2)。
Of course custom classes can even overload the operator!or operator<types can be convert to bool> to allow the !bfor their classes. For instance, std::streamhas overloaded the operator!and operator void*for checking the failbit, so that idioms like
当然，自定义类甚至可以重载operator!或operator<类型可以转换为 bool> 以允许!b它们的类。例如，std::stream重载了operator!andoperator void*来检查故障位，所以像这样的习语
while (std::cin >> x) { // <-- conversion to bool needed here
...
can be used.
可以使用。
(But your code !( a > b && b <= c) || a > c && !bis just cryptic.)
（但你的代码!( a > b && b <= c) || a > c && !b很神秘。）
回答by Amnon
Originally, in C (on which C++ is based) there was no Boolean type. Instead, the value "true" was assigned to any non-zero value and the value "false" was assigned to anything which evaluates to zero. This behavior still exists in C++. So for an int x, the expressions !xmeans "xnot true", which is "xnot non-zero", i.e. it's true if xis zero.
最初，在 C（C++ 所基于的）中没有布尔类型。相反，值“真”被分配给任何非零值，值“假”被分配给任何评估为零的值。这种行为在 C++ 中仍然存在。因此，对于 an int x，表达式的!x意思是“x不为真”，即“x非非零”，即如果x为零则为真。
回答by vitaut
You can, !bis equivalent to (b == 0).
可以，!b相当于(b == 0)。
回答by Armen Tsirunyan
The build-in !operator converts its argument to bool. The standard specifies that there exists a conversion from any arithmetic type(int, char,.... float, double...) to bool. If the source value is 0 the result is true, otherwise it is false
内置!运算符将其参数转换为bool. 该标准指定存在从任何算术类型( int, char,.... float, double...) 到 bool 的转换。如果源值为 0，则结果为true，否则为false
回答by Puppy
The test for int is true for non-zero values and false for zero values, so not is just true for zero values and false for non-zero values.
int 的测试对于非零值是真的，对于零值是假的，所以不仅零值是真的，非零值是假的。
