Read file into byte array

copy_file.cpp

// image is from: https://github.com/rust-lang/rust/issues/11562

#include <assert.h>  // assert
#include <fstream>   // std::ifstream
#include <vector>    // std::vector

std::vector<char> file_to_bytes(const char* filename) {
  // Seek to the end in advance to get the file size in an easier way.
  std::ifstream ifs(
      filename, std::ifstream::in | std::ifstream::binary | std::ifstream::ate);
  assert(!ifs.fail());

  // Get size of the file.
  std::streampos size = ifs.tellg();
  ifs.seekg(ifs.beg);  // Rewind the cursor before reading data.

  // Read the file data to byte array.
  std::vector<char> buffer;
  buffer.resize(size, 0);
  assert(buffer.size() == size);
  ifs.read(buffer.data(), static_cast<std::streamsize>(buffer.size()));

  ifs.close();
  return buffer;
}

void bytes_to_file(const char* filename, std::vector<char> buffer) {
  std::ofstream ofs(filename, std::ofstream::out | std::ofstream::binary);
  assert(!ofs.fail());
  ofs.write(buffer.data(), static_cast<std::streamsize>(buffer.size()));
  ofs.close();
}

bool are_files_same(const char* file1, const char* file2) {
  std::ifstream ifs1(file1, std::ifstream::binary | std::ifstream::ate);
  std::ifstream ifs2(file2, std::ifstream::binary | std::ifstream::ate);
  assert(!ifs1.fail() && !ifs2.fail());

  // Check file sizes.'
  if (ifs1.tellg() != ifs1.tellg()) {
    return false;
  }

  // Rewind files to their beginnings and compare their contents.
  ifs1.seekg(ifs1.beg);
  ifs2.seekg(ifs2.beg);
  bool same = std::equal(std::istreambuf_iterator<char>(ifs1.rdbuf()),
                         std::istreambuf_iterator<char>(),
                         std::istreambuf_iterator<char>(ifs2.rdbuf()));

  ifs1.close();
  ifs2.close();
  return same;
}

int main() {
  const char* source = "rust-logo-256x256.png";
  const char* copy = "rust-logo-256x256_copy.png";
  std::vector<char> bytes = file_to_bytes(source);
  bytes_to_file(copy, bytes);
  assert(are_files_same(source, copy));
  return 0;
}

rust-logo-256x256.png