Default constructor value for bool type

问题:

Which value does the default constructor of the bool type return in C++?

For instance, writing

int i = int();

guarantees that the variable i will be initiated always with 0.

I guess such an initialization routine is possible as well:

bool b = bool();

But unfortunately I could not find anywhere which value such a default bool constructor is defined to return. Is the variable b always initialized with false or true.

回答1:

false.

Seen in the C++14 draft N4296, section 8.5 (Initializers), paragraph 6, list item 1 and references therein, and paragraph 8, list item 4.

回答2:

bool is an integral type, and value-intialization should make it zero.

回答3:

Is the variable b always initialized with false or true?

false

Converting true to an integer type will yield 1, and converting false will yield 0 (4.5/4 and 4.7/4)

A very simple test code

#include<iostream>
int main()
{
  bool b=bool();

  if(!b)
  {
     std::cout<<"b: false";
  }

}

回答4:

The b is initialized also with zero.

回答5:

bool behaves 'as if it were declared':

enum bool {false,true};

It is an integral type and might be casted to int as values 0 and 1 (respectively), and its default value is false.