endian/example/endian_example.cpp

// endian_example.cpp  -------------------------------------------------------//

//  Copyright Beman Dawes, 2006

//  Distributed under the Boost Software License, Version 1.0.
//  See http://www.boost.org/LICENSE_1_0.txt

//  See library home page at http://www.boost.org/libs/endian

//----------------------------------------------------------------------------//

#include <boost/endian/detail/disable_warnings.hpp>

#include <iostream>
#include <cstdio>
#include <boost/endian/buffers.hpp>
#include <boost/static_assert.hpp>

using namespace boost::endian;

namespace 
{
  //  This is an extract from a very widely used GIS file format. Why the designer
  //  decided to mix big and little endians in the same file is not known. But
  //  this is a real-world format and users wishing to write low level code
  //  manipulating these files have to deal with the mixed endianness.

  struct header
  {
    big_int32_buf_at     file_code;
    big_int32_buf_at     file_length;
    little_int32_buf_at  version;
    little_int32_buf_at  shape_type;
  };

  const char* filename = "test.dat";
}

int main(int, char* [])
{
  header h;
  
  BOOST_STATIC_ASSERT(sizeof(h) == 16U);  // reality check

  h.file_code   = 0x01020304;
  h.file_length = sizeof(header);
  h.version     = 1;
  h.shape_type  = 0x01020304;

  //  Low-level I/O such as POSIX read/write or <cstdio> fread/fwrite is sometimes
  //  used for binary file operations when ultimate efficiency is important.
  //  Such I/O is often performed in some C++ wrapper class, but to drive home the
  //  point that endian integers are often used in fairly low-level code that
  //  does bulk I/O operations, <cstdio> fopen/fwrite is used for I/O in this example.

  std::FILE* fi = std::fopen(filename, "wb");  // MUST BE BINARY
  
  if (!fi)
  {
    std::cout << "could not open " << filename << '\n';
    return 1;
  }

  if (std::fwrite(&h, sizeof(header), 1, fi)!= 1)
  {
    std::cout << "write failure for " << filename << '\n';
    return 1;
  }

  std::fclose(fi);

  std::cout << "created file " << filename << '\n';

  return 0;
}