Passing a double pointer as argument to a function which expects a reference to a std::vector

Question

Is there any possible way to pass pointer to a double (double *) as argument to a function which expects a reference to a std::vector<double> argument in C++11

no, the types mismatch, you need to convert before you call in c++ — Wolfgang Brehm, Sep 27 '19 at 08:18
By 'double pointer' do you mean `double*` or a pointer to another pointer? — Peter Hull, Sep 27 '19 at 08:21
How would the function know the number of elements that are behind the `double*`? This is quite clearly impossible. — Max Langhof, Sep 27 '19 at 08:42

score 1 · Answer 1 · answered Sep 27 '19 at 09:59

1

That will not be possible, you'll have to copy the data in a vector

vector<double> v(ptr, ptr + length);

Also, you cannot assign the data behind the pointer directly in the vector, copying is required, see here

answered Sep 27 '19 at 09:59

Patrik

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score 1 · Answer 2 · answered Sep 27 '19 at 13:10

Rather than copying the data into a vector, you could also change the function to take a span. You will still have to include the length along with the pointer.

e.g.

void takes_span(std::span<double>) {}

int main()
{
    std::vector<double> vec = { 1, 2, 3 };
    double arr[3] = { 4, 5, 6 };
    double * ptr = arr;

    takes_span(vec);
    takes_span(arr);
    takes_span({ptr, 3});
}

Passing a double pointer as argument to a function which expects a reference to a std::vector

2 Answers2