流迭代器-字节流

Question

Reading files into an array of bytes can easily be accomplished using istream_iterator.

For example:

std::ifstream afile(somefile);
noskipws(afile);
...
std::vector<uint_8> vOfBytes = { std::istream_iterator<uint8_t>(afile),
                                 std::istream_iterator<uint8_t>() };

I now have a need to be able to do the same with vectors and strings. The problem is that these will very in size.

For example:

std::string astring = "abc";
std::wstring awstring = L"abc";
std::vector avector<uint32_t> = { 0, 1, 2, 3 };

// std::distance(asv.begin(), asv.end()) == 3
std::vector<uint8_t> asv = { /* astring to std::vector<uint8_t> */ }; 

// std::distance(awsv.begin(), awsv.end()) == 6
std::vector<uint8_t> awsv = { /* awstring to std::vector<uint8_t> */ };

// std::distance(uiv.begin(),uiv.end()) == 16
std::vector<uint8_t> uiv = { /* avectorto std::vector<uint8_t>*/};

I have been looking through the cpp reference for a bit and have not come across a way to treat the above as a stream of bytes w/o having to roll my own stream. Does anyone have any suggestions or references they could point me towards? I would greatly appreciate it.

Answer 1

You can use the very same iterator constructor

#include <string>
#include <vector>
#include <iostream>

int main()
{
  std::string astring = "abc";
  std::wstring awstring = L"abc";
  std::vector<uint32_t> avector{ 0, 1, 2, 3 };

  std::vector<uint8_t> asv{
    reinterpret_cast<uint8_t const*>(astring.data()),
    reinterpret_cast<uint8_t const*>(astring.data() + astring.size()),
  }; 

  std::vector<uint8_t> awsv{
    reinterpret_cast<uint8_t const*>(awstring.data()),
    reinterpret_cast<uint8_t const*>(awstring.data() + awstring.size()),
  }; 

  std::vector<uint8_t> uiv{
    reinterpret_cast<uint8_t const*>(avector.data()),
    reinterpret_cast<uint8_t const*>(avector.data() + avector.size()),
  };

  std::cout << std::hex;

  for (auto v : asv)
    std::cout << static_cast<int>(v) << ' ';
  std::cout << '\n';
  for (auto v : awsv)
    std::cout << static_cast<int>(v) << ' ';
  std::cout << '\n';
  for (auto v : uiv)
    std::cout << static_cast<int>(v) << ' ';
  std::cout << '\n';
}