A book exercise: Reading and writing to binary records through random access...
(The book is C++ without Fear)
I was able to get it to work one way, but was not able to get the authors solution. Actually he uses different commands then in the book examples, but I like his approach so I decided to try and solve his way. He uses functions in the control statements which I didn't in the first go around.
Here is my first try which works.
Code:
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <cstring>
using namespace std;
int get_int(int default_value);
int main() {
char filename[MAX_PATH + 1];
int n = 0;
int choice = 0;
char model[21];
char make[21];
char year[6];
int mileage = 0;
int recsize = sizeof(model) + sizeof(make) + sizeof(year) + sizeof(int);
cout << "Enter file name: ";
cin.getline(filename, MAX_PATH);
// Open file for binary read and write.
fstream fbin(filename, ios::binary | ios::out | ios::in);
if (!fbin) {
cout << "Could not open file " << filename << endl;
system("PAUSE");
return -1;
}
// Get record number to write to.
while(1){
cout << "What would you like to do?" << endl;
cout << "Enter 1 to write a record." << endl;
cout << "Enter 2 to read a record." << endl;
cout << "Enter 3 to quit" << endl;
cout << "Enter here: ";
choice = get_int(0);
if (choice == 3)
break;
if(choice == 1){
cout << "Enter file record number: ";
n = get_int(0);
// Get data from end user.
cout << "Enter model: ";
cin.getline(model, sizeof(model));
cout << "Enter make: ";
cin.getline(make, sizeof(make));
cout << "Enter year: ";
cin.getline(year, sizeof(year));
cout << "Enter mileage: ";
mileage = get_int(0);
// Write data to the file.
fbin.seekp(n * recsize);
fbin.write(model, sizeof(model) - 1);
fbin.write(make, sizeof(make) - 1);
fbin.write(year, sizeof(year) - 1);
fbin.write((char*)(&mileage), sizeof(int));
}
if (choice == 2){
cout << "Enter file record number: ";
n = get_int(0);
fbin.seekp(n * recsize);
// Read data from the file.
fbin.read(model, sizeof(model) - 1);
fbin.read(make, sizeof(make) - 1);
fbin.read(year, sizeof(year) - 1);
fbin.read((char*)(&mileage), sizeof(int));
// Display the data
cout << "The model is: " << model << endl;
cout << "The make is: " << make << endl;
cout << "The year is: " << year << endl;
cout << "The mileage is: " << mileage << endl;
}
if (choice != (1 || 2 || 3))
continue;
}
fbin.close();
system("PAUSE");
return 0;
}
#define COL_WIDTH 80 // 80 is typical column width.
// Get integer function
// Get an integer from keyboard; return default
// value if user enters 0-length string.
//
int get_int(int default_value) {
char s[COL_WIDTH + 1];
cin.getline(s, COL_WIDTH);
if (strlen(s) == 0)
return default_value;
return atoi(s);
}
and my second try which compiles, run, but it doesn't seem to write anything to the file and I get garbage back.
Code:
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <cstring>
using namespace std;
int get_int(int default_value);
void write_record();
void read_record();
int main() {
char filename[MAX_PATH + 1];
int n = 0;
int choice = 0;
cout << "Enter file name: ";
cin.getline(filename, MAX_PATH);
// Open file for binary read and write.
fstream fbin(filename, ios::binary | ios::out | ios::in);
if (!fbin) {
cout << "Could not open file " << filename << endl;
system("PAUSE");
return -1;
}
// Get record number to write to.
while(1){
cout << "What would you like to do?" << endl;
cout << "Enter 1 to write a record." << endl;
cout << "Enter 2 to read a record." << endl;
cout << "Enter 3 to quit" << endl;
cout << "Enter here: ";
choice = get_int(0);
if (choice == 1)
write_record();
else if(choice == 2)
read_record();
else if(choice == 3){
fbin.close();
system("PAUSE");
return 0;}
else
cout << "Bad Entry!!! Re-enter choice: " << endl << endl;
} //end while
} // end main
void write_record(){
int n = 0;
int choice = 0;
char model[21];
char make[21];
char year[6];
int mileage = 0;
int recsize = sizeof(model) + sizeof(make) + sizeof(year) + sizeof(int);
fstream fbin;
cout << "Enter file record number: ";
n = get_int(0);
cout << "Enter model: ";
cin.getline(model, sizeof(model));
cout << "Enter make: ";
cin.getline(make, sizeof(make));
cout << "Enter year: ";
cin.getline(year, sizeof(year));
cout << "Enter mileage: ";
mileage = get_int(0);
// Write data to the file.
fbin.seekp(n * recsize);
fbin.write(model, sizeof(model) - 1);
fbin.write(make, sizeof(make) - 1);
fbin.write(year, sizeof(year) - 1);
fbin.write((char*)(&mileage), sizeof(int));
}
void read_record(){
int n = 0;
int choice = 0;
char model[21];
char make[21];
char year[6];
int mileage = 0;
int recsize = sizeof(model) + sizeof(make) + sizeof(year) + sizeof(int);
fstream fbin;
cout << "Enter file record number: ";
n = get_int(0);
fbin.seekp(n * recsize);
// Read data from the file.
fbin.read(model, sizeof(model) - 1);
fbin.read(make, sizeof(make) - 1);
fbin.read(year, sizeof(year) - 1);
fbin.read((char*)(&mileage), sizeof(int));
// Display the data
cout << "The model is: " << model << endl;
cout << "The make is: " << make << endl;
cout << "The year is: " << year << endl;
cout << "The mileage is: " << mileage << endl;
}
#define COL_WIDTH 80 // 80 is typical column width.
// Get integer function
// Get an integer from keyboard; return default
// value if user enters 0-length string.
//
int get_int(int default_value) {
char s[COL_WIDTH + 1];
cin.getline(s, COL_WIDTH);
if (strlen(s) == 0)
return default_value;
return atoi(s);
}
any ideas? keep in mind I'm a beginner to C++, if you see any other errors I may be making please let me have it. Braces for impact.
Thanks all!
