Array of Bools

To use a genuine std::vector <T> one can specify T as unsigned char.

The sizeof (unsigned char) and sizeof (bool) on MSVC (and other compilers) are same.

EDIT: It seems that std::bitset is a non-STL container (source).

Quote:

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Originally Posted by MSDN

Unlike the similar vector<bool> Class, the bitset class does not have iterators and is not an Standard Template Library container.

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OK. OK. I missed the earlier references to bitset. So shoot me.

But still don't use vector<bool>...

Quote:

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Originally Posted by Graham

OK. OK. I missed the earlier references to bitset. So shoot me.

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No, we need you here... ;)

Quote:

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Originally Posted by cilu

The catch is that as long as false == 0, it doesn't matter what the sizeof(bool) is. Because two zeros on 1 byte or 165 bytes are equal. However, that doesn't work if want to set it to true, and true == 1. If bool had 2 bytes, each value would actually be 0x0101.

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a bool can be converted to an integer, and in that case, false is converted to zero, but i am not sure that false must be stored as zero. It may be stored as 42. But maybe the standard explicits something about the usage of memset on boolean arrays...

Quote:

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Originally Posted by SuperKoko

a bool can be converted to an integer, and in that case, false is converted to zero, but i am not sure that false must be stored as zero. It may be stored as 42. But maybe the standard explicits something about the usage of memset on boolean arrays...

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false is always zero.

Hence, this -

Code:

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if (mSomeCondition)
{
        // Do Something...
}

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is actually evaluated (since the legacy "C" days when no bool existed) as -

Code:

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if (mSomeCondition != 0)
{
        // Do Something...
}

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Here are some relevant quotes (source) -

Quote:

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4 An rvalue of type bool can be converted to an rvalue of type int, with false becoming zero and true becoming one.

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And...

Quote:

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If the source type is bool, the value false is converted to zero and the value true is converted to one.

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Actually, across many programming languages, I have observed that -

• false is always zero.
• true can take any non-zero value.

For instance, in VB: vbTrue has a value of -1, whilst vbFalse is 0 (Zero).

Hence, when one writes a C++ COM Component that transacts with a VB client (or vice-versa) one transacts VARIANT_BOOL data type to convey boolean information, and VARIANT_FALSE is valued at 0 (Zero) whilst VARIANT_TRUE is -1 (and could be anything else for that matter).

Right, because "-1" is the signed form of 0xFFFFFFFF.

Viggy

Quote:

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It may be stored as 42.

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Perhaps. But what compiler would store false as 42 if it must be converted to 0, and viceversa, from 0 to false? Frankly, this looks to me like a risk I would take... ;) (as the proverb says, he, who doesn't risk, does not win)

Quote:

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Originally Posted by cilu

Perhaps. But what compiler would store false as 42 if it must be converted to 0, and viceversa, from 0 to false? Frankly, this looks to me like a risk I would take... ;) (as the proverb says, he, who doesn't risk, does not win)

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Yes, the risk is inexistant.
Even, very weird compilers on very weird platforms probably use 0 to represent false.

But, on this point, i wonder why there is not a std::set template function that could assign all the items of an array to a specific value.
And this function could have specialized versions for primitive types (including bool) that could use memset.
And it could even be used to set all items of an array of boolean to true.

Quote:

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Originally Posted by SuperKoko

But, on this point, i wonder why there is not a std::set template function that could assign all the items of an array to a specific value.

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One can initialize the elements contained in a vector to a value via the constructor - as seen in my previous sample.

Otherwise std::transform comes close.

(The programmer needs to define the action to be taken.)

Quote:

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Originally Posted by SuperKoko

And this function could have specialized versions for primitive types (including bool) that could use memset. And it could even be used to set all items of an array of boolean to true.

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vector <bool> and std::bitset both feature:

• vector <bool>::flip
• std::bitset <T>::flip

...That can toggle boolean element states (which by default are constructed in a false state).