从csv文件c ++中删除一行

Question

Here I have a file that reading in to a vector

typedef struct contacts 
{
    string name;   //{jhonathan , anderson , felicia}
    string nickName; //{jhonny  , andy , felic}
    string phoneNumber; // {13453514 ,148039 , 328490}
    string carrier;  // {atandt , coolmobiles , atandt }
    string address; // {1bcd , gfhs ,jhtd }

} contactDetails;

vector <contactDetails> proContactFile;

I want to let user to delete a contact record from the file.For this I wrote a code.But from the code that i've written it deletes all the contact details from the file.But what I want here is when a user types a name then the program should delete only the name and the relevent nickname,carrier,phone number and address belongs to that name.Here is the code that i've written

    string readString, selectContact;
    cout << "Enter the name you want to delete" << endl;
    cin >> selectContact;
    ifstream fin;
    fin.open(contactsFile); 
    if (!fin.is_open())
    {
        cout << "Unable to open Contacts.csv, please make sure file exists!" << endl;
    }
   
    ofstream fout;
    fout.open("temp.csv" , ios::out);

    while (getline(fin, readString))
    {
        if (((readString = readString.find(selectContact), 0)) == 0)
        {
            fout << readString  <<',' << "\n";
            
        }
        cout << "Deleted Successfully" << endl;
        showTableContacts();
    }
    if (((readString = readString.find(selectContact), 0) != 0))
    {
        cout << "\n" << selectContact << " not found" << endl;
    }
   
    fout.close();
    fin.close();
    remove("Contact.csv");//Deletes contacts.csv file
    rename("temp.csv" , "Contact.csv");//Rename temp file as Contacts.csv
}

Answer 1

if (((readString = readString.find(selectContact), 0)) == 0)

This line has several issues.

1. readString.find(selectContact) returns the index of the match, or string::npos if it's not found. Checking that it is an exact match at position 0 is ok, technically, however, in your case if your string is "abcdefg" and you search for "abc" it will also match at position 0 when it shouldn't. You need to ensure the entire field matches, not just the first characters of it. (Find the first ',' in your line then ensure that all the bytes from the beginning up to the comma match your contact.)

2. Next consider this part:

   readString = readString.find(selectContact)

You are assigning the result of the find to your string. That is, if find() returns 3, you will assign 3 to your string, which is interpreted as an ASCII character, and now your readString contains a single byte with junk in it. (In ASCII, 'A' is 65, etc)

So now your string is obliterated, and the index of your match is the contents, in the first byte (if the value is in range, or undefined behavior if it overflows.)

3. Code of this form:

   if (xxx, 0)

is utilizing the comma operator , which sequences expressions by evaluating them from left to right, applying side effects (but throwing away the results) and the full expression evaluates to the value of the rightmost expression. Whatever xxx does (in your case, xxx is the code in step 2 above, obliterating your string) its return value is discarded and this whole expression evaluates to 0, which converts to a bool as false . Every time. (1,2,3) evaluates to 3, etc.

Therefore:

(readString = readString.find(selectContact), 0)

always evaluates to 0. And

if (((readString = readString.find(selectContact), 0)) == 0)

always obliterates your string, then tests if 0==0 which is always true.

Also, you almost never want to delete your input files. Rewriting them is dangerous enough, but you must be absolutely sure that everything succeeded before doing so; otherwise your program can end up causing a lot of pain if it deletes the input file and nothing else.