如何习惯地将``char *``转换为``double *``

Question

I'm relearning C++, and I'm trying to work with boost::iostreams::mapped_file . This class maps file data to char* , I'd like to cast it to double* (since I'm working with doubles).

I could cast it using C-style cast: double* foo = (double*) data , but I'm trying go use idiomatic C++, and C++ favours C++ casts like: static_cast and so on.

I came up with:

double* data = static_cast<double*>((void*)file.data());

(file->data returns char* ). Which really isnt cleaner.

Here is what I'm trying to do (this code works!):

BOOST_AUTO_TEST_CASE(OpenMMapArray){

typedef boost::multi_array_ref<double, 3> arrayd3;
typedef std::array<size_t, 3> index3d;

index3d shape = {{ 20, 20, 20 }};

size_t size = sizeof(double)*std::accumulate(shape.begin(), shape.end(), 1, std::multiplies<size_t>());

boost::iostreams::mapped_file file;

boost::iostreams::mapped_file_params params;

params.path = "/tmp/mmaptest-2";
params.mode = std::ios::in | std::ios::out;
params.new_file_size =  size;

file.open(params);

double* data = static_cast<double*>((void*)file.data());

arrayd3 array(data, shape);

array[0][0][0] = 20;
array[0][1][0] = 19;
array[1][0][0] = 18;
array[0][0][5] = 17;

BOOST_CHECK(data[0] == 20);
BOOST_CHECK(data[20] == 19);
BOOST_CHECK(data[20*20] == 18);
BOOST_CHECK(data[5] == 17);

file.close();
}

Answer 1

In this particular case, you actually are trying to re-interpret the data as a different type. So a reinterpret_cast is in order:

double* data = reinterpret_cast<double*>(file.data());