Organizing a Virtual Filesystem - Android NDK Game Development - page 97

How to do it...

1. Let us derive the FileWriter class from the iOStream interface. We add the

Open() and Close() member functions on top of the iOStream interface and
carefully implement the Write() operation. Our output stream implementation does
not use memory-mapped iles and uses ordinary ile descriptors, as shown in the
following code:
class FileWriter: public iOStream
{
public:
FileWriter(): FPosition( 0 ) {}
virtual ~FileWriter() { Close(); }

bool Open( const std::string& FileName )
{
FFileName = FileName;

2. We split Android and Windows-speciic code paths using deines:
#ifdef _WIN32
FMapFile = CreateFile( FFileName.c_str(),
GENERIC_WRITE, FILE_SHARE_READ, NULL, CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL, NULL );
return !( FMapFile == ( void* )INVALID_HANDLE_VALUE );
#else
FMapFile = open( FFileName.c_str(), O_WRONLY|O_CREAT );
FPosition = 0;
return !( FMapFile == -1 );
#endif
}

3. The same technique is used in the other methods. The difference between both

OS systems is is trivial, so we decided to keep everything inside a single class and
separate the code using deines:

void Close()
{
#ifdef _WIN32
CloseHandle( FMapFile );
#else
if ( FMapFile != -1 ) { close( FMapFile ); }
#endif
}