external_libraries/boost_endian/libs/integer/example/endian_example.cpp

   1 // endian_example.cpp  -------------------------------------------------------//
   2
   3 //  Copyright Beman Dawes, 2006
   4
   5 //  Distributed under the Boost Software License, Version 1.0.
   6 //  See http://www.boost.org/LICENSE_1_0.txt
   7
   8 //  See library home page at http://www.boost.org/libs/endian
   9
  10 //----------------------------------------------------------------------------//
  11
  12 #define _CRT_SECURE_NO_DEPRECATE  // quiet VC++ 8.0 foolishness
  13
  14 #include <iostream>
  15 #include <cassert>
  16 #include <cstdio>
  17 #include <boost/integer/endian.hpp>
  18
  19 using namespace boost::integer;
  20
  21 namespace
  22 {
  23   //  This is an extract from a very widely used GIS file format. I have no idea
  24   //  why a designer would mix big and little endians in the same file - but
  25   //  this is a real-world format and users wishing to write low level code
  26   //  manipulating these files have to deal with the mixed endianness.
  27
  28   struct header
  29   {
  30     big32_t     file_code;
  31     big32_t     file_length;
  32     little32_t  version;
  33     little32_t  shape_type;
  34   };
  35
  36   const char * filename = "test.dat";
  37 }
  38
  39 int main()
  40 {
  41   assert( sizeof( header ) == 16 );  // requirement for interoperability
  42
  43   header h;
  44
  45   h.file_code   = 0x04030201;
  46   h.file_length = sizeof( header );
  47   h.version     = -1;
  48   h.shape_type  = 0x04030201;
  49
  50   //  Low-level I/O such as POSIX read/write or <cstdio> fread/fwrite is sometimes
  51   //  used for binary file operations when ultimate efficiency is important.
  52   //  Such I/O is often performed in some C++ wrapper class, but to drive home the
  53   //  point that endian integers are often used in fairly low-level code that
  54   //  does bulk I/O operations, <cstdio> fopen/fwrite is used for I/O in this example.
  55
  56   std::FILE * fi;
  57
  58   if ( !(fi = std::fopen( filename, "wb" )) )  // MUST BE BINARY
  59   {
  60     std::cout << "could not open " << filename << '\n';
  61     return 1;
  62   }
  63
  64   if ( std::fwrite( &h, sizeof( header ), 1, fi ) != 1 )
  65   {
  66     std::cout << "write failure for " << filename << '\n';
  67     return 1;
  68   }
  69
  70   std::fclose( fi );
  71
  72   std::cout << "created file " << filename << '\n';
  73   return 0;
  74 }