如何使用 remove() 重命名和删除 c++ 中的 txt 文件以更新内容？

Question

I have these 2 files and I need to update the file by updating into the temp file. I did it but how do I rename the temp file to the old file and then delete the old file?

ifstream in_file;
ofstream temp_file;

char in_file_name[] = "input practical 12 part d.txt";
char temp_file_name[] = "temp.txt";

I tried to do like this and the file name don't change. I need some explanation on this and how it works. This is the site I referred to and I don't understand it. https://www.programiz.com/cpp-programming/library-function/cstdio/rename

in_file.close();
temp_file.close();

int rename(char *temp_file_name, char *in_file_name);

Also, can I update the file by renaming the temp file to the old file and then rename the old file to temp file so that the user don't need to recreate a temp file to update the contents in the file?

Here's the whole code just in case

1. Write and test a program that reads product details from a file and stores the information in an array of structures. The program then prints a menu to allow the user to do any of the following:
2. List all products
3. Search the price of a product
4. Update the price of a product
5. Exit

If the user chooses to exit, the program will write the updated data in the array of structures to the file. The product information includes product number, description and price.

Note: You may assume that the total number of product details read from the file will not exceed 30, the product number consist of 6 numbers, and the product description will not exceed 30 characters.

#include <iostream>
#include <iomanip>
#include <fstream>
#include <cstring>
#include <string>
#include <cstdio>
using namespace std;

typedef struct
{
    char product_num[5];
    char product_des[29];
    float price;
    
}PRODUCT_TYPE;

int main()
{
    ifstream in_file;
    ofstream temp_file;

    char in_file_name[] = "input practical 12 part d.txt";
    char temp_file_name[] = "temp.txt";
    in_file.open(in_file_name);
    temp_file.open(temp_file_name);

    if (!in_file || !temp_file)
    {
        if (!in_file)
        {
            cout << "Error opening input file" << endl;
        }
        else if (!temp_file)
        {
            cout << "Error opening output file" << endl;
        }
    }
    else
    {
        PRODUCT_TYPE product[50];
        int index = -1;
        int choice;
        string line;
        in_file >> product[++index].product_num;
        cout << "Succesful run" << endl;
        cout << "Menu (Type number for the function)" << endl;
        cout << "1. List all products\n2.Search the price of a product\n3.Update the price of a product\n4.Exit\n";
        cin >> choice;
        if (choice == 1)
        {
            cout << setw(18) << left << "Product Index" << setw(35) << left << "Product Description" << "Price" << endl;
        }
        
        else if (choice == 4)
        {
            cout << setw(18) << left << "Product Index" << setw(35) << left << "Product Description" << "Price" << endl;
        }

        while (in_file)
        {
            in_file >> product[index].product_des >> product[index].price;
            if (choice == 1)
            {
                cout << setw(18) << left << product[index].product_num << setw(35) << left << product[index].product_des << product[index].price << endl;

            }
            else if (choice == 2)
            {
                cout << "Type the product number to get the price" << endl;
                cout << "Product Number: ";
                cin >> product[index].product_num;
                cout << "Price: ";
                cout << product[index].price << endl;
            }
            
            else if (choice == 3)
            {
                float new_price;
                cout << "Enter the product number to change its price: ";
                cin >> product[index].product_num;
                cout << "Enter the updated price list: ";
                cin >> new_price;
                if (new_price != product[index].price)
                {
                    temp_file << " " << product[index].product_num << " "<< product[index].product_des << " "<< new_price << endl;
                }

            }

            else if (choice == 4)
            {
                cout << setw(18) << left << product[index].product_num << setw(35) << left << product[index].product_des << product[index].price << endl;
            }
            in_file >> product[++index].product_num;
        }
        
        in_file.close();
        temp_file.close();

        int rename(char *temp_file_name, char *in_file_name);
    }
    return 0;

}

Thanks.

Answer 1

What this is telling you:

int rename(char *temp_file_name, char *in_file_name);

is that there's a method called rename that takes two arguments. You've defined your two file names like this:

char in_file_name[] = "input practical 12 part d.txt";
char temp_file_name[] = "temp.txt";

So I believe you've written temp.txt, and now you want to move it into place over the other one with the really obnoxious name.

rename(temp_file_name, in_file_name);

Beware: this destroys the original input file, so if you want to save it:

rename(in_file_name, "copy_of_input.txt");

Does that make sense?