CSci351 Introduction to File Processing: Homework 2 Solutions

CSci351 Introduction to File Processing: Homework 2 Solutions

Due date: Friday, February 15, 2008 in class
Each homework may have a different weight, which depends on its level of difficulty.
Absolutely no copying others' work

Rewrite the extraction(>>) operator of the file readstr.cpp of Figure 4.4 (Page 124) in textbook, so that it uses the following field representations: (70%)

Method 1, fixed length fields.
Ans>

istream &  operator >> ( istream & stream, Person & p ) {
  stream.getline( p.LastName,  30 );
  if ( strlen( p.LastName ) == 0 )  return( stream );
  stream.getline( p.FirstName, 30 );
  stream.getline( p.Address,   30 );
  stream.getline( p.City,      30 );
  stream.getline( p.State,     15 );
  stream.getline( p.ZipCode,   10 );
  return( stream );
}

Method 2, fields with length indicators.
Ans>
Assume there is a space after the length.

istream &  operator >> ( istream & stream, Person & p ) {
  int   len;
  char  space;
 
  stream >> len;     stream >> space;
  stream.getline( p.LastName,  len );
  if ( strlen( p.LastName ) == 0 )  return( stream );
  stream >> len;     stream >> space;
  stream.getline( p.FirstName, len );
  stream >> len;     stream >> space;
  stream.getline( p.Address,   len );
  stream >> len;     stream >> space;
  stream.getline( p.City,      len );
  stream >> len;     stream >> space;
  stream.getline( p.State,     len );
  stream >> len;     stream >> space;
  stream.getline( p.ZipCode,   len );
  return( stream );
}

Method 4, fields with keyword tags.
Ans>
Assume that

the format of the keyword tags is “keyword=value,”
the maximum length of keyword is less than 32 bytes,
the maximum length of value is less than 256 bytes, and
the delimiter is ‘|’.

istream &  operator >> ( istream & stream, Person & p ) {
  char  keyword[32];
  for ( int i = 0;  i < 6;  i++ ) {
    stream.getline( keyword, 32, '=' );
    if ( strncmp( keyword, "LastName", strlen( "LastName" ) ) == 0 )
      stream.getline( p.LastName,  256, '|' );
    else if ( strncmp( keyword, "FirstName", strlen( "FirstName" ) ) == 0 )
      stream.getline( p.FirstName, 256, '|' );
    else if ( strncmp( keyword, "Address", strlen( "Address" ) ) == 0 )
      stream.getline( p.Address, 256, '|' );
    else if ( strncmp( keyword, "City", strlen( "City" ) ) == 0 )
      stream.getline( p.City, 256, '|' );
    else if ( strncmp( keyword, "State", strlen( "State" ) ) == 0 )
      stream.getline( p.State, 256, '|' );
    else if ( strncmp( keyword, "ZipCode", strlen( "ZipCode" ) ) == 0 )
      stream.getline( p.ZipCode, 256, '|' );
    else if ( strlen( keyword ) == 0 )  return( stream );
  }
  return( stream );
}

Suppose you need to keep a file in which every record has both fixed- and variable-length fields. For example, suppose you want to create a file of employee records, using fixed-length fields for each employee's ID (primary key), sex, birth date, and department, and using variable length fields for each name and address. (30%)
- What advantages might there be to using such a structure?
  Storage utilization is improved and it is more flexibility in designing record structure.
- Should we put the variable-length portion first or last?
  Put the variable length part at the end, since this makes it easiest to find and process the fixed length part.
- Either approach is possible; how can each be implemented?
  There are many ways to implement this structure. One example is to place a delimiter after each variable-length field and put the fixed-length fields just as what they are.