Re: Seeking and Reading a CFile

I am having trouble trying to execute multiple Read calls on a CFile.

I can execute the first Read fine, reading in BUFFER_LENGTH bits...
I then loop through the data, reading and handling different data types
(In my example below, I only showed one case but other types are
similar), I just use one byte to distinquish between different types.
After finding out the type, I check to make sure that the entire
structure made it in the buffer, if not I then try to reposition the file
pointer by dwRead-i, such that the first byte read in is the same type
identifier and I can resume reading the entire type.

I thought this should work, however on the second Read, dwRead = 0,
meaning no bytes were read.

What did I do wrong?

Here is the code:

Cfile file;
file.Open(...);

while((dwRead = file.Read(buffer, BUFFER_LENGTH)) > 0){
   bool refill;
   for(int i = 0 ; i < dwRead;i++)
   {
       //first make sure there was enough room to read next byte (size
byte)
       if(i == (dwRead -1)){
           //the type identifier was the last byte, reposition -1 and get
another chunk
           file.Seek( -(dwRead - i) , CFile::current);
           break;
       }
       refill = false;
       switch(buffer[i])
       {
           case DATAPT:
               if( (i + sizeof(DataPt) ) >= dwRead-1){
                   file.Seek( -(dwRead - i) , CFile::current);
                   refill = true;
               }
               else{
                   handleDataPt((DataPt*) &buffer[i+1]);
                   i += sizeof(DataPt);//advance i past size of DataPt to
next type Identifier
                }
               break;
         }
          if(refill)
               break;
       }

   if(refill && dwRead != BUFFER_LENGTH)
       break;//requested to refill, however it was end of
file...corrupted data
}
file.Close();

Thanks,

Nick