Is there a standard way to replace a C-style bool array?

Question

In this piece of code

void legacyFunction(int length, bool *bitset)
{
    // stuff, lots of stuff
}

int main()
{
    int somenumber = 6;
    // somenumber is set to some value here

    bool *isBitXSet = new bool[somenumber];
    // initialisation of isBitXSet.

    legacyFunction(somenumber, isBitXSet);

    delete[] isBitXSet;
    return 0;
}

I'd like to replace bool *isBitXSet = new bool[somenumber]; by something like

std::vector<bool> isBitXset(somenumber, false);

But I cannot do

legacyFunction(somenumber, isBitXSet.data());

because data() doesn't exist for std::vector<bool>. And I cannot change the interface of legacyFunction().

Is there a good alternative to the C-style bool array?

Note that the missing data() member function is not the only problem. std::vector<bool> is a specialization that may provide a more space-efficient implementation. So the elements of vector<bool> and a C-style bool array may not overlap. — jfMR
– jfMR, Commented Sep 8, 2017 at 11:33
@moooeeeep Yeah, right, sorry. Normally I would delete the question by myself. But I like the answer given by Vittorio Romeo much more than any of those answers from 2009. — TobiMcNamobi
– TobiMcNamobi, Commented Sep 8, 2017 at 11:40
No need to worry. I just wanted to have them linked and thought they might be related close enough to have them as duplicate. Others might disagree. — moooeeeep
– moooeeeep, Commented Sep 8, 2017 at 12:42

Vittorio Romeo · Accepted Answer · 2017-09-08 11:24:31Z

8

You can use std::unique_ptr<T[]> and std::make_unique:

int main()
{
    int somenumber = 6;
    // somenumber is set to some value here

    auto isBitXSet = std::make_unique<bool[]>(somenumber);    
    // initialisation of isBitXSet.

    legacyFunction(somenumber, isBitXSet.get());

    return 0;
}

Alternatively, you can "trick" std::vector by creating your own bool wrapper:

struct my_bool { bool _b; };
std::vector<my_bool> v; // will not use `vector<bool>` specialization

If you know the size of your array at compile-time, consider using std::array.

edited Sep 8, 2017 at 11:24

answered Sep 8, 2017 at 11:18

Vittorio Romeo

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6 Comments

Rakete1111 Over a year ago

Isn't std::array also a possibility?

Vittorio Romeo Over a year ago

@Rakete1111: not if somenumber is a run-time value, as in the example.

TobiMcNamobi Over a year ago

Nice answer! In your second example: How would I apply this to make the function call? Like this legacyFunction(somenumber, reinterpret_cast<bool*>(v.data()));?

Vittorio Romeo Over a year ago

@TobiMcNamobi: that will probably work but I am unsure about its safety and standard-compliance. Only use that after proper research. I would suggest going with unique_ptr.

Andre Kostur Over a year ago

@TobiMcNamobi How about legacyFunction(somenumber, &v[0]); ?

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