datastore.h

A template solution for C++ database development Description: A template class that can write,read,

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// datastore.h
// defines a template class to handle record files
// Author: Vijay Mathew Pandyalakal
// Date: 12/23/2001 11:08:12 AM
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


#ifndef DATASTORE_H
#define DATASTORE_H

#include <cstdio>
#include <string>
using namespace std;

template <class T>
class DataStore {
	private:
		char FileName[26];
		FILE* fp;
	public:
		//~~~~~ function default constructor ~~~~~~~~~~~~~~~~~~
		// initializes FileName to ""
		// arguments: null
		// null
		// returns null
		DataStore() {
			strcpy(FileName,"");
		}
		//~~~~~~ end of function default constructor~~~~~~~~~~~~~~~~~


		//~~~~~ function overloaded constructor ~~~~~~~~~~~~~~~~~~
		// initializes filename
		// arguments: const char*
		// copied to file name
		// returns null
		DataStore(const char* fnm) {
			strcpy(FileName,fnm);
		}
		//~~~~~~ end of function oveloaded constructor~~~~~~~~~~~~~~~~~

		
		//~~~~~ function SetFileName ~~~~~~~~~~~~~~~~~~
		// sets a new file name
		// arguments: const char*
		// arg is copied to FileName
		// returns void
		void SetFileName(const char* fnm) {
			strcpy(FileName,fnm);
		}
		//~~~~~~ end of function SetFileName~~~~~~~~~~~~~~~~~

		//~~~~~ function Open ~~~~~~~~~~~~~~~~~~
		// opens a file in read/write binary mode
		// arguments: null
		// null
		// returns true if file open succeeds
		bool Open() {
			fp = fopen(FileName,"rb+");
			if(fp == NULL) {
				fp = fopen(FileName,"wb+");
			}
			if(fp == NULL) {
				return false;
			}
			return true;
		}
		//~~~~~~ end of function Open~~~~~~~~~~~~~~~~~

		//~~~~~ function AddRecord ~~~~~~~~~~~~~~~~~~
		// appends a record to the file
		// arguments: T
		// arg is the variable of an unspecified class
		// returns true on success
		bool AddRecord(T t) {
			fseek(fp,0,SEEK_END);
			if(fwrite((char*)&t,sizeof(T),1,fp)) {
				return true;
			}else {
				return false;
			}
		}
		//~~~~~~ end of function AddRecord~~~~~~~~~~~~~~~~~

		//~~~~~ function FindRecord ~~~~~~~~~~~~~~~~~~
		// searches for a record in the file
		// arguments: unsigned long
		// arg is the index position of the record in file
		// returns record if found
		T FindRecord(unsigned long index) {
			rewind(fp);
			unsigned long pos = index * sizeof(T);
			fseek(fp,pos,SEEK_CUR);
			T t;
			fread((char*)&t,sizeof(T),1,fp);
			return t;
		}
		//~~~~~~ end of function FindRecord~~~~~~~~~~~~~~~~~

		//~~~~~ function ModifyRecord ~~~~~~~~~~~~~~~~~~
		// modifies a record in file
		// arguments: T,unsigned long
		// write the first arg to position specified by 2nd arg
		// returns true on success
		bool ModifyRecord(T newT,unsigned long index) {
			rewind(fp);
			unsigned long pos = index * sizeof(T);
			fseek(fp,pos,SEEK_CUR);
			if(fwrite((char*)&newT,sizeof(T),1,fp)) {
				return true;
			}else {
				return false;
			}
		}
		//~~~~~~ end of function ModifyRecord~~~~~~~~~~~~~~~~~

		//~~~~~ function DeleteRecord ~~~~~~~~~~~~~~~~~~
		// deletes a record form file
		// arguments: unsigned long
		// arg specifies the index of record to delete
		// returns true on success
		bool DeleteRecord(unsigned long index) {
			rewind(fp);
			FILE* tmp;
			char tmp_fnm[36];
			strcpy(tmp_fnm,"tmp.pln");
			//strcat(tmp_fnm,FileName);
			tmp = fopen(tmp_fnm,"wb");
			if(tmp == NULL) {
				return false;
			}
			unsigned long idx = 0;
			T t;
			while((fread((char*)&t,sizeof(T),1,fp)) == 1) {
				if(idx != index) {
					fwrite((char*)&t,sizeof(T),1,tmp);
				}//else {
				//	printf("Index: %d\n",index);
				//}
				idx++;
			}
			fclose(fp);
			fclose(tmp);
			tmp = fopen(tmp_fnm,"rb");
			fp = fopen(FileName,"wb+");
			if(fp != NULL) {
				rewind(fp);
				rewind(tmp);
				while((fread((char*)&t,sizeof(T),1,tmp)) == 1) {
					fwrite((char*)&t,sizeof(T),1,fp);
				}
				fclose(tmp);
				fclose(fp);
				fopen(FileName,"rb+");
				unlink(tmp_fnm);
				return true;
			}else {
				return false;
			}
		}
		//~~~~~~ end of function DeleteRecord~~~~~~~~~~~~~~~~~

		//~~~~~ function GetRecordCount ~~~~~~~~~~~~~~~~~~
		// counts number of record in file
		// arguments: null
		// 0
		// returns record count
		unsigned long GetRecordCount() {
			fseek(fp,0,SEEK_END);
			unsigned long len = ftell(fp);
			unsigned long recs = len / sizeof(T);
			return recs;
		}
		//~~~~~~ end of function GetRecordCount~~~~~~~~~~~~~~~~~

		//~~~~~ function Close ~~~~~~~~~~~~~~~~~~
		// closes the file
		// arguments: 0
		// 0
		// returns void
		void Close() {
			fclose(fp);
		}
		//~~~~~~ end of function Close~~~~~~~~~~~~~~~~~

		//~~~~~ function GetNextRecordNo ~~~~~~~~~~~~~~~~~~
		// finds the maximum id + 1 to uniquely identify a record
		// arguments: 0
		// 0
		// returns next id
		unsigned long GetNextRecordNo() {
			rewind(fp);
			unsigned long ret = 0;
			T t;
			while((fread((char*)&t,sizeof(T),1,fp)) == 1) {
				if(t.id > ret) {
					ret = t.id;
				}
			}
			ret += 1;
			return ret;
		}
		//~~~~~~ end of function GetNextRecordNo~~~~~~~~~~~~~~~~~

};
#endif

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// end of datastore.h
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~