Trouble reading in data from a file using data structures - c++

Question

I have a program with car rental information and the company as well. I am trying to read it in and have it display on the terminal. However, I am only getting one company to print clearly, while the others print out only trash. I want to store the agencies with a car inventory of 5 as well, but don't exactly know how to store them without having all my information read in yet. I can only use C-Style strings also.
Here is the file I am reading in:
Hertz 93619
2014 Toyota Tacoma 115.12 1
2012 Honda CRV 85.10 0
2015 Ford Fusion 90.89 0
2013 GMC Yukon 110.43 0
2009 Dodge Neon 45.25 1
Alamo 89502
2011 Toyota Rav4 65.02 1
2012 Mazda CX5 86.75 1
2016 Subaru Outback 71.27 0
2015 Ford F150 112.83 1
2010 Toyota Corolla 50.36 1
Budget 93035
2008 Ford Fiesta 42.48 0
2009 Dodge Charger 55.36 1
2012 Chevy Volt 89.03 0
2007 Subaru Legacy 59.19 0
2010 Nissan Maxima 51.68 1
Section of my code where I need help:
#include <iostream>
#include <fstream>
using namespace std;
struct car
{
char agency[10];
int zip;
int year;
char make[10];
char model[10];
float price;
int available;
} ;
struct agency
{
char company[10];
int zip;
int inventory[5];
};
void menu();
// Main Function
int main ()
{
// declare variables
const int carAmount = 15;
int agencyAmount = 1;
int choice;
agency agencyLib[carAmount];
car carLib[carAmount];
char filename[10];
ifstream carInData;
bool menu1 = false;
//prompt user for input file
cout << " Enter file name: ";
cin >> filename;
// Start loop menu
while(menu1 = true)
{
menu();
carInData.open(filename);
cin >> choice;
if (carInData.is_open())
{
// read list of names into array
for (int count = 0; count < agencyAmount; count++)
{
carInData >> agencyLib[count].company >> agencyLib[count].zip;
for (count = 0; count < carAmount; count++)
{
carInData >> carLib[count].year >> carLib[count].make >> carLib[count].model >> carLib[count].price >> carLib[count].available;
}
}
}
switch (choice)
{
// Case 1 closes menu
case 1:
return 0;
break;
// Case 2 displays if car is available if 1, unavailable if 0
case 2:
// itterate through car array
for(int count = 0; count < agencyAmount; count++)
{
cout << agencyLib[count].company << " " << agencyLib[count].zip << "\n";
for(int count = 0; count < carAmount; count++)
{
// Displays if car is available or not
/* if (carLib[count].available == 1)
cout << " Available ";
else
cout << " Unavailable ";
*/
// Display Cars
cout << carLib[count].year << " " << carLib[count].make << " " << carLib[count].model << " " << carLib[count].price << " " << "\n";
}
}
}
}
}

Answer 1

As a general preliminary remark, I think that even for learning purpose, this kind of exercise should better let you use std::strings instead of c-strings and std::vector for keeping a growing number of items.
What's wrong in your code ?
The first problem is that you use the same counter count to populate your agency array AND the car array. This will cause you very quickly to have a counter beyond the array boundaries and corrupt memory.
Solution: rework your loop structure using 2 distinct counters.
Next problem is that you don't identify the end of the car list of an agency. This makes it unrealistic to read more than one agency: you'll experience a failure on the stream reading that will prevent you getting anything usefull in your data.
Solution: analyze failures on reading to identify going from cars ( first element should be a number) to a new agency ( first element is a string).
In addition, you might have some strings which are longer than allowed by your character arrays, causing further memory corruption.
Solution: limit the number of chars read using iomanip() to fix maximum width. This is strongly recommended unless you go for std::string
Last issue: the variable length arrays are not a standard C++ feature, even if some popular compilers support it.
Solution: Either use dynamic allocation with new/delete or opt for the purpose of this excercise to use a constant maximum size.
Code snippet:
Adapted, without choices, menus, etc. , the reading would look like:
const int carAmount = 30; // !!!
const int agencyAmount = 10; // !!!
agency agencyLib[carAmount];
car carLib[carAmount];
ifstream carInData ("test.dat");
int numCar = 0, numAgency = 0; // !!! shows the real number of items available
int count1, count2; //
cout << "Start reading" << endl;
for (numAgency = numCar = 0; carInData && numAgency < agencyAmount; numAgency++) {
if (!(carInData >> setw(sizeof(agencyLib[numAgency].company)) >> agencyLib[numAgency].company >> agencyLib[numAgency].zip))
break; // if nothing left, exit loop immediately
for (; numCar < carAmount; numCar++) {
carInData >> carLib[numCar].year >> setw(sizeof(carLib[numCar].make )) >>carLib[numCar].make
>> setw(sizeof(carLib[numCar].model))>>carLib[numCar].model
>> carLib[numCar].price >> carLib[numCar].available;
if (carInData.fail()) { // here we expect a year, but get an agency string
carInData.clear();
break;
}
strcpy(carLib[numCar].agency, agencyLib[numAgency].company);
carLib[numCar].zip = agencyLib[numAgency].zip;
}
}
And the subsequent display:
cout << "Display agencies: " << endl;
for (count1 = 0; count1 < numAgency; count1++) {
cout << agencyLib[count1].company << " " << agencyLib[count1].zip << "\n";
}
cout << "Cars: " << endl;
for (count2 = 0; count2 < numCar; count2++) {
cout << carLib[count2].agency << " " << carLib[count2].zip << ": ";
cout << carLib[count2].year << " " << carLib[count2].make << " " << carLib[count2].model << " " << carLib[count2].price << " " << "\n";
}
Note that there's no link beteween agencies and cars (except the common fields), so the display just shows two distinct lists.