Strange Behaviour initializing bool

[crispin]

Hi,

I was under the impression that bool's were false by default... Am I wrong about this?

In VC++6, when I define a bool in a class header (i.e. bool testbool) and then access it BEFORE I have initialized it to a definite value, it returns 1. I am sure that I have not accidentally initialized it to true anywhere. Just curious, is it supposed to be this way?

Cheers,
Crispin

[sicarie]

Hi,

I was under the impression that bool's were false by default... Am I wrong about this?

In VC++6, when I define a bool in a class header (i.e. bool testbool) and then access it BEFORE I have initialized it to a definite value, it returns 1. I am sure that I have not accidentally initialized it to true anywhere. Just curious, is it supposed to be this way?

Cheers,
Crispin

C/C++ considered any number not 0 to be 1, and will return that value unless the memory location it allocates to the boolean value is all 0's, which is not likely.

Basically - it creates the space for the variable in memory, and that space holds whatever value is there, before you initialize it. Once you initialize it, that value is wiped out, but before you do, you are accessing memory that is part of some other program or file's temp space, that is now free.

[willakawill]

Right. This is the case with all variables in c++. Unless you give them an initial value you are left with the garbage at that particular memory address.

[crispin]

Perfect - This explains a lot. Thanks for your advice :)

[vishwanathntandasi]

Hi,

I was under the impression that bool's were false by default... Am I wrong about this?

In VC++6, when I define a bool in a class header (i.e. bool testbool) and then access it BEFORE I have initialized it to a definite value, it returns 1. I am sure that I have not accidentally initialized it to true anywhere. Just curious, is it supposed to be this way?

Cheers,
Crispin

since bools can take only two values
by default it should be zero .due some mistake in the system hardware it might happen

[sicarie]

since bools can take only two values
by default it should be zero .due some mistake in the system hardware it might happen

That's not true, actually - there is nothing wrong with the OP's hardware.

Check it for yourself - I just did (though for some reason I get an error when I try to copy and paste, so can't copy my code...) But if you initialize four values to: any arbitrarily large number, one that is large and negative, one to one, and one to zero, then put them all in if statements that print, the only one in gcc that will not print is the one with 0. This is a compiler quirk, not a hardware problem.

[willakawill]

since bools can take only two values
by default it should be zero .due some mistake in the system hardware it might happen

Nonsense. The compiler has to treat any non zero value as true or 1. This is called undefined behaviour because we don't know what will be at that memory address without initializing the variable, bool or otherwise.