deleting line in linux text file with C++ - c++

Question

i need help in how i should write a code for doing a delete line using c++ in linux. what i have in the text file is listed below
description:amount:date
electricity bill:100:25jan2015
telephone bill:100:25jan2015
telephone bill:50:25jan2015
i want to do it so that when the user selects option b to remove the expense that the user input and to prevent the program from deleting duplicate data the user will have to input the amount and date. thank you.
and the temp.txt is used to store what was not deleted before being renamed to Expense.txt so if telephone bill value 100 was removed it would become
electricity bill:100:25jan2015
telephonebill:50:25jan2015
void deleteexpensesdata(string& expense, string& texpense, double& amount, string& date){
int check, x=0;
ifstream Expenses("Expense.txt");
ofstream temp("temp.txt");
cout << "\n";
cout << "Enter Type of Expense you wish to remove" << endl;
cin >> texpense;
while(Expenses >> expense >> amount >> date){
if(texpense!=expense){//if there are expenses with different name, input their data into temp file
temp << expense << ":" << amount << ":" << date <<endl;
}
if(texpense==expense){// if user entered correct name, x=1 for later output message that the user data has been deleted
x=1;
}
}
Expenses.clear();
Expenses.seekg(0, ios::beg);
Expenses.close();
temp.close();
remove("Expense.txt");
rename("temp.txt","Expense.txt");
if(x==0){//x was set to 0 at start, so if it didn't change, it means there is error
cout << "Remove of Expense failed" << endl;
}
else{//if x is not = 0 then remove is successful
cout << "Expenses has been removed" << endl;
}
}
the code that calls the function is below
cout << "Remove Expense.\n";
deleteexpensesdata(expense, texpense, amount, date);
cout << "Expense Date has been delete. \n" << endl;
cin.ignore();
cin.get();

Answer 1

This code below gets the user input and converts the double to string and turns all 3 variable into line with the delimiter ":" as seen in your example input and after u open the file u get the line that does not match into a temp file and rename the file essentially removing it.
double expamt;
string line, expdesc, exptrans;
cout << "Please Enter Expense: \n";
cin >> expdesc;
cout << "Please Enter Amount: \n";
cin >> expamt;
string newamt = static_cast<ostringstream*>( &(ostringstream() << expamt) )->str();
cout << "Date of Transaction: (e.g 20jan2015)\n";
cin >> exptrans;
string input = expdesc + ":" + newamt + ":" + exptrans;
ifstream myfile;
ofstream tempfile;
myfile.open("Expense.txt");
tempfile.open("temp.txt");
while (getline(myfile, line))
{
if (line != input)
tempfile << line;
}
cout << "\nExpense " << expdesc << " has been removed \n" <<endl;
myfile.close();
tempfile.close();
remove("Expense.txt");
rename("temp.txt", "Expense.txt");

Answer 2

First an advice: You should learn to use gdb.
Your code has several logic errors, for instance the line:
Expenses >> expense >> amount >> date
might not be doing what you're expecting to do, since the operator >> don't deal (by default) with character ':' as a separtor or delimiter.
Also, don't use a variable (x) for checking input errors, ifstream and ofstream objects has functions like: ifstream::good, ifstream::fail and ifstream::bad.
However you could user a x for check if any change was made, if not you don't need the file operations:
remove("Expense.txt");
rename("temp.txt","Expense.txt");
Said that, your comment con be readed:
x was set to 0 at start, so if it didn't change, it means there is error
Actually that's wrong, x == 0 also means the condition texpense==expense never got true.
Recomendations
You could use std::iftream::getline and change the delimiter to :.
You could use std::iftream::getline combined with regex and std::regex::search.
I think the first is easier (if : aren't sorrounded by spaces), the second is more elegant as less error prone. Is up to you.