First: sorry as a relative newbie for previously not including code.
My question:
Reading C++ books I almost always find programs such as the one below
give the following type of code for reading a file :
//********* BUM CODE *************************************
infile.open ("test.dat" , ios::in);
while (!infile.eof())
{
infile.read ((char *)&dog, sizeof (dog)); // read from file
cout << "Dog Name = " << dog.name << endl;
cout << "Dog age = " << dog.age << endl;
cout << "Dog weight = " << dog.weight << endl;
}
infile.close();
//************************************************** ****************
If you use this you find that the last record to be read is always
displayed twice!
Nowhere in the books can I find a mention, nor a solution to this.
My solution .. and I am always looking for the simplest to understand ..
is to use the 'read-ahead' technique to read the file
//***** READ AHEAD METHOD ****************************
infile.open ("test.txt" , ios::in);
infile.read ((char *)&dog, sizeof (dog)); // read ahead first record
while (!infile.eof())
{
cout << "Dog Name = " << dog.name << endl;
cout << "Dog age = " << dog.age << endl;
cout << "Dog weight = " << dog.weight << endl;
infile.read ((char *) &dog, sizeof (dog)); // read next record
}
infile.close();
//***********************************
This appears to work .. but as I have not seen this used anywhere I
wondered if there is anything wrong with it as a method?
Is there a better way?
//****** FULL BUM PROGRAM ****************************
#include <fstream>
#include <cstdlib>
#include <ctype.h> // needed for toupper()
#include <string>
using namespace std;
void StoreFileData(fstream& outfile);
void RetrieveFileData(fstream& infile);
class doggie // used basically as a structure
{
public:
char name[20] ;
int age;
float weight ;
};
//***********************************
int main()
{
fstream f;
StoreFileData(f);
RetrieveFileData(f);
system("PAUSE");
return 0;
}
//************************************
void StoreFileData(fstream& outfile)
{
doggie dog ;
char answer = 'Y';
outfile.open ("test.txt" , ios::out);
do
{
cout << "Enter dog name :";
cin >> dog.name;
cout << "What is " << dog.name << "\'s age : " ;
cin >> dog.age;
cout << "What is " << dog.name << "\'s weight : " ;
cin >> dog.weight;
outfile.write ((char *)&dog, sizeof (dog));
cout << "\nAny more dogs (y/n)?: ";
cin >> answer ;
answer = toupper (answer);
}
while (answer != 'N');
outfile.close();
}
//***********************************************
void RetrieveFileData(fstream& infile)
{
doggie dog ;
cout << "\nReading the file back now " << endl;
infile.open ("test.txt" , ios::in);
while (!infile.eof())
{
infile.read ((char *)&dog, sizeof (dog)); // read record
cout << "Dog Name = " << dog.name << endl;
cout << "Dog age = " << dog.age << endl;
cout << "Dog weight = " << dog.weight << endl;
}
infile.close();
}
//***********************************
