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Zero is used to represent false, and One is used to represent true. For interpretation, Zero is interpreted as false and anything non-zero is interpreted as true. To make life easier, C Programmers typically define the terms "true" and "false" to have values 1 and 0 respectively.
Boolean values and operations There are just two values of type bool: true and false. They are used as the values of expressions that have yes-or-no answers. C++ is different from Java in that type bool is actually equivalent to type int. Constant true is 1 and constant false is 0.
bool "bar" is by default true, but it should be false, it can not be initiliazied in the constructor. is there a way to init it as false without making it static?
Using a bool IMO reflects its use much better than using an int . In fact, before C++ and C99, C89 didn't have a Boolean type. Programmers would often typedef int Bool in order to make it clear that they were using a boolean.
Yes. The casts are redundant. In your expression:
true == 1
Integral promotion applies and the bool value will be promoted to an int and this promotion must yield 1.
Reference: 4.7 [conv.integral] / 4: If the source type is bool... true is converted to one.
Charles Bailey's answer is correct. The exact wording from the C++ standard is (§4.7/4): "If the source type is bool, the value false is converted to zero and the value true is converted to one."
Edit: I see he's added the reference as well -- I'll delete this shortly, if I don't get distracted and forget...
Edit2: Then again, it is probably worth noting that while the Boolean values themselves always convert to zero or one, a number of functions (especially from the C standard library) return values that are "basically Boolean", but represented as ints that are normally only required to be zero to indicate false or non-zero to indicate true. For example, the is* functions in <ctype.h> only require zero or non-zero, not necessarily zero or one.
If you cast that to bool, zero will convert to false, and non-zero to true (as you'd expect).
According to the standard, you should be safe with that assumption. The C++ bool type has two values - true and false with corresponding values 1 and 0.
The thing to watch about for is mixing bool expressions and variables with BOOL expression and variables. The latter is defined as FALSE = 0 and TRUE != FALSE, which quite often in practice means that any value different from 0 is considered TRUE.
A lot of modern compilers will actually issue a warning for any code that implicitly tries to cast from BOOL to bool if the BOOL value is different than 0 or 1.
I've found different compilers return different results on true. I've also found that one is almost always better off comparing a bool to a bool instead of an int. Those ints tend to change value over time as your program evolves and if you assume true as 1, you can get bitten by an unrelated change elsewhere in your code.
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