Deleting content from a file [closed] - c++

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I am making a program that allows a user to make bank accounts and save them too a file, you can also delete them. I am having issues with my code for deleting an account on the file, my function for deleting the account looks like this.
int deleteCustomer(account acc[], int numCust)
{
string target;
bool accFound = false;
int count = 0;
cout << "Enter account number: ";
cin >> target;
for (int i = 0; i < numCust; i++)
{
if (acc[i].acctNum == target)
{
accFound = true;
break;
}
count++;
}
if (accFound == false)
{
cout << "That account does not exist." << endl;
system("pause");
system("cls");
}
else if (accFound == true)
{
ofstream outFile;
outFile.open("customer.dat");
for (int i = count; i < numCust - 1; i++)
{
outFile << acc[i+1].acctNum;
outFile << '#';
outFile << acc[i+1].name;
outFile << '#';
outFile << acc[i+1].cBal;
outFile << '#';
outFile << acc[i+1].sBal;
outFile << '#';
}
numCust--;
outFile.close();
}
return numCust;
}
The function is supposed to overwrite the account selected by the user by saving the file ahead of it to the previous spot and return the new number of customers. It appears to run through fine but it does not do anything and I am uncertain as to why. Any input would be helpful, thank you.

Answer 1

Several problems here:
Your account lookup should be working, but you're overcomplicating this a bit (you'd only need one value rather than three, but let's skip that for now). If you're interested let me know.
You're never actually removing any account (just reducing the number of total accounts; which will then cause the last entry to be removed).
When saving you accounts to the file, you start at that selected index, which doesn't make any sense at all.
Let's assume you've got 10 accounts, indices 0 through 9.
The user picks the account at index 5.
You save accounts index 6 through 9(!) only.
The user picks the account at index 0.
You save accounts index 1 through 9 only.
Some style things:
You essentially store the selected account's index in count. That's fine, but very misleading. Don't ever use misleading variable names. As you might be able to tell from my comment above, I misread that part as well.
Rather than writing if (booleanValue == true) you could just write if (booleanValue), which results in the same code, but is shorter and might be faster to read. In a similar way, you could replace if (booleanValue == false) with !booleanValue.
Don't omit namespaces like std, if you can (e.g. use std::string rather than string and avoid using namespace std;) to avoid writing ambigious code. If some other namespace you use has string (or any other member) as well, you'll either have to explicitly name the namespace anyway or you're at least confusing others reading your code. Also there's always the potential bug introduced by unintentionally using a different type.
Fixing the actual problem:
I assume this is some homework assignment or some tutorial/class code or anything similar? If so, don't just copy the following code and instead try to think about how it's working. Once you understood, implement it yourself and only use my snippets if you're really stuck.
In general, it's good software design to keep code and functions minimal. Don't create "super functions" that do several things. Also try to make code reusable, so in case you change something, you're able to adjust it in one place only.
Take your code above for example. Whenever you add, delete, or update an account, you'll have to write the new file. Did you plan on replicating the same code multiple times? If you'd have to adjust your file format, you'd have to change it everywhere.
You'll also need some way to actually remove customer datasets. As you might be aware, deleteing entries in an array would require you to move all entries behind it (to keep it continguous). This can be a very expensive operation.
To avoid this, I'm adding a new member bool valid to account. By default, this is set to false. Once there's some data put there (either through reading from a file or by the user), it's value is set to true.
So instead split this into two separate functions (moving the common code - saving - to its own function):
// By returning an integer value, you're able to communicate issues or problems
// without having to rely on exceptions (in case you're using C++).
// Note that I don't do any error checking here for simplicity.
// Parameters:
// filename - the target file to write
// acc - the array holding all customer accounts
// size - the maximum amount of values in acc
// Return value: 0, if everything went fine
// (I skipped actual error handling to keep it simple!)
int saveCustomers(const char *filename, account acc[], int size) {
std::ofstream outFile(filename);
// Iterate over all entries
for (int i = 0; i < num; ++i) {
// Do we actually have to store the account?
if (acc[i].valid) {
outfile << acc[i].acctNum << '#' << acc[i].name; // write all the values the way you did
}
}
outFile.close();
return 0; // Everything ok
}
Now that this is done, you're able to create your functions to modify your customer data:
int deleteCustomerByNumber(account acc[], int num, std::string target) {
// Iterate over all accounts and look for the selected one
for (int i = 0; i < num; ++i) {
// Only check valid accounts and see whether it's the target
if (acc[i].valid && acc[i].acctNum == target) {
acc[i].valid = false; // Mark it as invalid
return 0; // Everything ok
}
}
return 1; // Didn't find it!
}
In a similar way you can look for empty/unused entries to actually write data to them.
Bonus - alternative (STL) approach:
Since you're using C++, I'd suggest you use a different data structure, not just a simple array:
If you use a STL container (more specific: a map), you're able to handle everything a lot easier.
#include <map>
// Create a typedef to simplify expressions
typedef std::map<std::string, account> accmap;
// All accounts would be stored in this object:
accmap accounts;
// To do a quick lookup of any account:
accmap::const_iterator a = accounts.find(accountNumber);
if (a == accounts.end())
;// Account not found!
else {
a->first; // This is your account number
a->second; // This is your `account` object
}
// To delete a specific account:
accounts.erase(accountNumber)
// To create a new account simply access it:
accounts[accountNumber].name = newName;

Answer 2

You need to save all of the records before the index and after the index, otherwise you are effectively deleting more than just the one account. Presumably you should also remove the record from the input array as well. You are also not doing any error handling on the input or output. And you need to fix your output loop, it is not using indexes correctly.
Try this:
int deleteCustomer(account acc[], int numCust)
{
string target;
int accFound = -1;
cout << "Enter account number: ";
if (cin >> target)
{
for (int i = 0; i < numCust; ++i)
{
if (acc[i].acctNum == target)
{
accFound = i;
break;
}
}
}
if (accFound == -1)
{
cout << "That account does not exist." << endl;
system("pause");
system("cls");
}
else
{
for (int i = accFound+1; i < numCust; ++i)
acc[i-1] = acc[i];
--numCust;
ofstream outFile;
outFile.open("customer.dat");
for (int i = 0; (i < numCust) && (outFile); ++i)
{
outFile << acc[i].acctNum;
outFile << '#';
outFile << acc[i].name;
outFile << '#';
outFile << acc[i].cBal;
outFile << '#';
outFile << acc[i].sBal;
outFile << '#';
}
if (!outFile)
cout << "Error saving customer file" << endl;
}
return numCust;
}
If you don't want to update the array, then you can do this instead:
int deleteCustomer(account acc[], int numCust)
{
string target;
int accFound = -1;
cout << "Enter account number: ";
if (cin >> target)
{
for (int i = 0; i < numCust; ++i)
{
if (acc[i].acctNum == target)
{
accFound = i;
break;
}
}
}
if (accFound == -1)
{
cout << "That account does not exist." << endl;
system("pause");
system("cls");
}
else
{
ofstream outFile;
outFile.open("customer.dat");
for (int i = 0; (i < numCust) && (outFile); ++i)
{
if (i != accFound)
{
outFile << acc[i].acctNum;
outFile << '#';
outFile << acc[i].name;
outFile << '#';
outFile << acc[i].cBal;
outFile << '#';
outFile << acc[i].sBal;
outFile << '#';
}
}
if (!outFile)
Cout << "Error saving customer file" << endl;
--numCust;
}
return numCust;
}
Lastly, when updating a file, it is a good idea to write the new data to a temp file first, then replace the original file with the temp file only if everything is successful. That way you reduce the risk of corrupting the original file.

Answer 3

To "deleting an account on the file", this part of code:
for (int i = count; i < numCust - 1; i++)
{
outFile << acc[i+1].acctNum;
outFile << '#';
outFile << acc[i+1].name;
outFile << '#';
outFile << acc[i+1].cBal;
outFile << '#';
outFile << acc[i+1].sBal;
outFile << '#';
}
should be
for (int i = 0; i < numCust; i++)
{
if(i == count) continue;// remove the account user selected
outFile << acc[i].acctNum;
outFile << '#';
outFile << acc[i].name;
outFile << '#';
outFile << acc[i].cBal;
outFile << '#';
outFile << acc[i].sBal;
outFile << '#';
}