Question

我无法确定如何使用close函数关闭文件，因为我在一个单独的函数中打开了一个文件。现在我的程序主要包括3个功能，创建，打开和关闭。创建和打开工作正常，但在我打开文件并返回到我的选项菜单后，我试图能够在没有任何用户输入的情况下关闭文件。我希望close函数检测哪个文件是打开的，然后关闭它。在我打开的时候应该只允许打开一个文本文件（我无法编码，但我假设工作与关闭函数相同）。以下是我的所有代码，还有其他功能我还需要实现，但我现在只担心前三个。谢谢你的帮助！

#include <iostream>
#include <fstream>
#include <stdio.h>

using namespace std;

void createDB() {
    ofstream db;
    string fileName;

    cout << "Enter the name of the database you want to create: \n";
    getline (cin, fileName);

    string fullFile = fileName + ".txt";

    std::ifstream fin(fullFile);

    if(fin.good()){ // means filename already exists
       cout << "\nCould not create database because database name " << fullFile << " is already taken\n";
    }
    else{ // creates file
        cout << "\nYour database " << fullFile << " was created successfully\n";
        db.open(fullFile);
    }

    db.close();
}

void openDB() {
    // need to add check to see if one is already open
    string fileName;

    cout << "Enter the name of the database you want to open: \n";
    getline (cin, fileName);

    string fullFile = fileName + ".txt";

    std::ifstream db(fullFile);

    if(db.good()){ // means file exists
        cout << "\nThe database " << fullFile << " has been opened successfully\n";
        db.open(fullFile);
    }

    else{ // there is no file named that to open
      cout << "\nThere is no database named " << fullFile << " to open\n";
    }
}


void closeDB() {

    cout << "The database _______ has been closed successfully";
}

void display() {
    cout << "Enter the ID of the employee you want to display: \n";
}

void update() {

}

void report() {

}

void add() {

}

void del() {

}

int menu() {
    cout << "Enter the number of the operation you wish to perform (1-9)\n"
    << "1. Create new database\n"
    << "2. Open database\n"
    << "3. Close database\n"
    << "4. Display record\n"
    << "5. Update record\n"
    << "6. Create report\n"
    << "7. Add a record\n"
    << "8. Delete a record\n"
    << "9. Quit\n";

    int sel = 0;
    (std::cin >> sel).ignore();

    switch (sel) {
        case 1: createDB();
            menu(); // after creating file go back to list of options
            break;

        case 2: openDB();
            menu();
            break;

        case 3: closeDB();
            menu();
            break;

        case 4: display();
            break;

        case 5: update();
            break;

        case 6: report();
            break;

        case 7: add();
            break;

        case 8: del();
            break;

        case 9: return 0;
            break;

        default: cout << "Please try again and enter a valid number\n\n";
            menu();
            break;
    }
    return true; // to avoid error saying control may reach end of non-void function
}


int main() {

    menu();

return 0;
}

Answer 1

您必须从打开的文件中接收文件描述符。 c stile： FILE * myfile; myfile = fopen（myfile，“r”）; 你可以继续阅读：http://www.cprogramming.com/tutorial/cfileio.html（我认为在c中它更容易理解，它也适用于c ++）。 c ++ stile http://www.cprogramming.com/tutorial/lesson10.html 他解释得非常好。

但你应该记住： 1）你必须创建一个指针（这是他唯一的数据不会丢失的方式）。 2）您必须发送/接收描述符

多个函数之间的文件i / o c ++

1 个答案: