3.1.1 Binary I/O

First, with fixed size structures, it is more storage efficient to use the binary representation of data. The C stream functions to use are fread and fwrite. Both functions has a parameter to specify how big (in bytes) each ``thing'' is, and how many things to read or write.

In Linux and all POSIX compliant operating systems, fopen can no longer open a file as ``text'' or ``binary''. In a POSIX compliant operating system, a file is just a file. The distinction between ``cooked'' versus ``raw'' is at the TTY (teletype) device level, not a per file level. You can use the function termios (and other related functions) to control attributes of a terminal device.

The following code illustrates how to perform structure-based binary I/O operations:

{
  FILE *pFile;
  struct X someStruct;
  // open a file so pFile points to the stream
  // stuff someStruct with data
  if (!fwrite(&someStruct, sizeof(someStruct), 1, pFile))
  {
    // error handling
    // why can't we write to the file?
    
  }
  // to read from pFile
  if (!fread(&someStruct, sizeof(someStruct), 1, pFile))
  {
    // error handling
    // why can't we read from the file? EOF?
  }
}