Comparing an std::array to a traditional array C++

Question

I am trying to perform a comparison of elements in:

std::vector<std::array<uint8_t, 6> > _targets =
{
  { 0x00, 0x00, 0x00, 0x00, 0x00, 0x11 }
  { 0x00, 0x00, 0x00, 0x00, 0x00, 0x22 }
};

to a traditional array:

 uint8_t _traditional[6] =  { 0x00, 0x00, 0x00, 0x00, 0x00, 0x33 }

as:

  for (auto target : _targets) 
  {

     if (! memcmp(target, _traditional, 6)) {
        known = 1;
     } 
  }

and am receiving a data conversion error:

error: cannot convert 'std::array<unsigned char, 6u>' to 'const void*' for argument '1' to 'int memcmp(const 
void*, const void*, size_t)

What is the propert byte wise comparison operation I can perform to accomplish equality evaluation?

Answer 1

You can use the data() member of array to get a pointer to the contained array:

if (! memcmp(target.data(), _traditional, 6))

The alternative of using &target[0] will work in this case (where you're storing a uint8_t) but won't work if you store a class that overloads the unary & (address) operator. But you could use std::addressof(target[0]) which will work even in the presence of an overloaded address operator.