Bool (C++) - Revision history

VolodyA! V Anarhist: released

2015-05-13T07:04:13Z

released

VolodyA! V Anarhist at 09:15, 11 May 2015

2015-05-11T09:15:33Z

VolodyA! V Anarhist: oops

2015-05-11T07:21:10Z

oops

VolodyA! V Anarhist: Created page with "{{FormatInfo | name = bool (C++) | formattype = electronic | subcat = Data types | subcat2 = C++ data types | subcat3 = | subcat4 =..."

2015-05-11T06:05:11Z

Created page with "{{FormatInfo | name = bool (C++) | formattype = electronic | subcat = Data types | subcat2 = C++ data types | subcat3 = | subcat4 =..."

New page

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| name = bool (C++)
| formattype = electronic
| subcat = Data types
| subcat2 = C++ data types
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{{DISPLAYTITLE:bool (C++)}}

'''bool''' can store one of two potential values '''true''' or '''false'''. Theoretically it can be done using a single bit of memory, however, RAM cannot be addressed by a single bit, therefore at least one byte is used most of the time. This opens the question which bit should be used to determine truth value, in C++ any bit set to 1 means that the value is true, however, when the literal constant '''true''' generates an integer value 1 (a single lowest bit being 1, the rest set to 0).

{| class='wikitable'
! 7 !! 6 !! 5 !! 4 !! 3 !! 2 !! 1 !! 0 !! value
|-
| 1 || 0 || 0 || 0 || 0 || 0 || 0 || 0 || true
|-
| 0 || 1 || 1 || 1 || 1 || 1 || 1 || 1 || true
|-
| 0 || 0 || 0 || 0 || 0 || 0 || 0 || 0 || '''false'''
|-
| 0 || 0 || 0 || 0 || 0 || 0 || 0 || 1 || '''true'''
|}

In bold you see the definition of these constants. When converting literal constant '''true''' to an integer type, you are guaranteed to get 1, converting '''false''' always yields 0.

However, different "true" values will evaluate as equal when being compared.
<pre>#include <iostream>

union crazyBool
{
unsigned char uc;
bool b;
};

int main()
{
crazyBool a, b;
a.uc = 1;
b.uc = 5;

if(a.b == b.b)
{
std::cout << "==" << std::endl;
}
else
{
std::cout << "!=" << std::endl;
}
return 0;
}</pre>

This code will return "!="

==Storing in a single bit==
It is possible to potentially store several bools together in less memory than if there were stored separately. This is done by placing them in a single byte, and reading their values by bit-shifting and bitwise AND operation. For example [[std::vector]] container has the specialisation for storing bool values, which does exactly that [http://www.cplusplus.com/reference/vector/vector-bool/].

==Other C++ data types of the same size==
There is no other data type that can be stored in a single bit, but there are several which use a single byte.
* [[char (C++)|char]]
* [[signed char]]
* [[unsigned char]]

[[Category:Enumerable data types]]

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 }</pre>
-This code will return "!="
+This code will return "!=". However the following code returns "==":
 ==Storing in a single bit==

@@ Line 38: / Line 38: @@
 In bold you see the definition of these constants. When converting literal constant '''true''' to an integer type, you are guaranteed to get 1, converting '''false''' always yields 0.
-However, different "true" values will evaluate as equal when being compared.
+However, different "true" values will '''not''' evaluate as equal when being compared.
 <pre>#include <iostream>