ScanTable.cc

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <cstring>
#include <string>
#include "ScanTable.h"

using namespace std;

int ScanTable::Open(char *relname)
{
   if ( (fp = fopen("catalog", "r")) == NULL )
   {
      cout << "Error: cannot open database catalog `./catalog'" << endl;
      return 0;
   }

   n_fields = 0;
   record_size = 0;

   /* ==================================================
	 Read attribute information on relation "relname"
      ================================================== */
   while ( fscanf(fp, "%s %s %c %d %d",
             DataDes[n_fields].relname, DataDes[n_fields].fieldname,&DataDes[n_fields].fieldtype,
             &DataDes[n_fields].startpos,&DataDes[n_fields].fieldsize) > 0 ){
       if ( strcmp( DataDes[n_fields].relname, relname ) == 0 ){
         if ( DataDes[n_fields].startpos + DataDes[n_fields].fieldsize >record_size ){
            record_size = DataDes[n_fields].startpos 
                         + DataDes[n_fields].fieldsize;
         }
         n_fields++;
       }
   }

   fclose(fp);

   if ( n_fields > 0 ){
      if ( (fd = open(relname, O_RDWR)) == -1 ){
          cout << "Error: canot open relation file " << relname << endl;
          return 0;
      }

      strcpy( TableName, relname);

      return 1;
   }
    
   else
      return 0;		// Relation not found
   
}

/* ==================================================
   GetNext(): read next tuple

     The tuple is return in this->buf

     return 1 for OK
            0 for error
   ================================================== */
int ScanTable::GetNext()
{ 
   int n;

   n =(int) read(fd, buf, record_size+1);

   if ( n == record_size+1 )
   {
      return 1;
   }
   else
   {
      return 0;
   }
}

void ScanTable::Close()
{
   close(fd);		// Close relation file
}



/* ================================================================
   getAttrType(attrName): Get data type of attr attrName
   ================================================================ */
int ScanTable::getAttrType( char *attrName )
{
   int i;

   for ( i = 0; i < n_fields; i++ )
   {
      if ( strcmp( attrName, DataDes[i].fieldname ) == 0 )
         return DataDes[i].fieldtype;
   }

   return -1;		// Attribute not found...
}



/* ================================================================
   getAttrSize(attrName): Get size of attr attrName
	(Only necessary for 'C' typed attributes)
   ================================================================ */
int ScanTable::getAttrSize( char *attrName )
{
   int i;

   for ( i = 0; i < n_fields; i++ )
   {
      if ( strcmp( attrName, DataDes[i].fieldname ) == 0 )
         return DataDes[i].fieldsize;
   }

   return -1;		// Attribute not found...
}


/* ================================================================
   getAttrPtr(attrName): return the pointer to attribute attrName
			 in buf[ ]
   ================================================================ */
void * ScanTable::getAttrPtr( char *attrName )
{
   int i;

   for ( i = 0; i < n_fields; i++ )
   {
      if ( strcmp( attrName, DataDes[i].fieldname ) == 0 )
         return &buf[ DataDes[i].startpos ];
   }

   return NULL;		// Attribute not found...
}




/* ================================================================
   PrintTuple(): print the tuple in buf[ ]
   ================================================================ */
void ScanTable::PrintTuple()
{
   int j;

   for (j = 0; j < n_fields; j++)
   {
      int    *i_ptr;   // To access an int variable
      double *f_ptr;   // To access a  "float" (= double) variable
      char   *c_ptr;   // To access a  char[ ] variable (string)

      if ( DataDes[j].fieldtype == 'I' )
      {
         i_ptr = (int *) &(buf[ DataDes[j].startpos]) ;
         printf("%d ", *i_ptr );         // *i_ptr is an int variable
      }
      else if ( DataDes[j].fieldtype == 'F' )
      {
         f_ptr = (double *) &(buf[ DataDes[j].startpos]) ;
         printf("%lf ", *f_ptr );         // *f_ptr is a double variable
      }
      else
      {
         c_ptr = (char *) &(buf[ DataDes[j].startpos]) ;
         printf("'%s' ", c_ptr );        // String is a (char *)
      }
   }

   printf("|| -- Valid flag: %c\n", buf[record_size] );
}

void ScanTable::PrintRelationInfo()
{
   int i;

   printf("\nThe relation contains these fields:\n");
   for (i = 0; i < n_fields; i++)
      cout << DataDes[i].relname << "." << DataDes[i].fieldname <<
		"\ttype = " << DataDes[i].fieldtype <<
		"\tstartpos = " << DataDes[i].startpos <<
		"\tsize = " << DataDes[i].fieldsize << endl;

   cout << endl << endl;
}


void ScanTable::Write(int fd, char c){
    lseek(fd,-1, SEEK_CUR);
    write(fd,&c,1);
}

bool ScanTable:: findAttr(char  *attrName){
    int i;
    
    for ( i = 0; i < n_fields; i++ )
    {
        if ( strcmp( attrName, DataDes[i].fieldname ) == 0 )
            return true;
    }
    
    return false;		// Attribute not found...

}