#include <scan.h>

Scan provide a tuple-by-tuple interface for accessing the content of a HeapFile object.

Relative Methods

Scan *HeapFile::OpenScan(Status &status)

This function initializes a new Scan for a HeapFile. If status is OK, success. Otherwise, fail.
After calling this function, you may use Scan::GetNext to retrieve the first record in the Heapfile.
You can also first call Scan::MoveTo to move to the record you wish to start with, and then call
Scan::GetNext to retrieve that record.

This function initializes a new Scan for a BTreeFile. Input lowKey and highKey of the range of scan.
After calling this function, you may use Scan::GetNext to retrieve records whose keys fall in the range
of lowkey and highkey. You may also use BTreeFile::OpenScan, but it is less efficient.

Get next record in BTreeFile. Output  : rid  - record id of the scanned record.
keyPtr -  a pointer to it's key value( You should allocate space for it before calling).
Return Status: OK if success. Done if there are no more records. Fail if error.
You can fetch the data of this record by calling HeapFile::GetRecord.

Methods

Status GetNext(RecordID &rid, char *recPtr, int &len)

Retrieve the next record from the HeapFile related with this scan. The content of the record will be copied into the memory location pointed to by recPtr. len will be set to the length of the record in bytes and rid will be set to the record id of the record. Return OK if a record is returned succesfully (including the last record). Return DONE if there are no more records. Return FAIL if something failed.

It will also update the currRid of Scan to the next rid. So, you can rpeatedly call this function  to retrieve all the records in a heapfile.
 

Set the current RecordID being scanned to the RecordID with record id rid. Calling GetNext() after MoveTo(rid) will return the record with record id rid. Return OK if successful and FAIL otherwise.

Here is a typical example how Scan class is used.

typedef struct Record {
    int i;
    float f;
} Record;

Status s;
HeapFile *f = new HeapFile("foo", s); // Open an existing HeapFile of type Record
if (s != OK)
{
    cerr << "Cannot open HeapFile foo\n";
}

Scan *scan = f->OpenScan(s);
if (s != OK)
{
    cerr << "Cannot open scan on foo\n";
}

int len;
Record r;
RecordID rid;
while (scan->GetNext(rid, (char *)&r, len) == OK)
{
    cout << r.i << " " << r.j << "\n";
}