无法使用 C++ 中的类成员函数创建/写入文件

Question

这是 MedClass.cpp :-

#include "MedClass.h"


std::string Medicine::getFileName()
{
    return file_name;
}

std::string Medicine::getMedicineName()
{
    return med_name;
}

std::string Medicine::getMedicineFormula()
{
    return med_formula;
}

void Medicine::displayMedInfo()
{
    std::cout << "Details of selected medicine : \n\n";
    std::cout << "Medicine name :- " << med_name << std::endl;
    std::cout << "Medicine formula :- " << med_formula << std::endl;
    std::cout << "Medicine weight :- " << med_weight << std::endl;
    std::cout << "Medicine Price :- " << med_price << std::endl;
    std::cout << "Medicine Expiry Date :- " << expiry_date << std::endl;
    std::cout << "Meicine Comapny :- " << med_company << std::endl;
}

int Medicine::getMedUnitsLeft()
{
    return med_units_left;
}

void Medicine::writeToFile()
{


    medicine_file.open(file_name);
    std::cout << "Enter details of medicine in following format :- \n";
    std::cout << "Name Formula Weight Price Company Expiry\n";
    getline(std::cin, file_input);
    medicine_file << file_input;
    medicine_file.close();
    std::cout<<"File input validated : \n";
}

void Medicine::getFromFile()
{
    medicine_file.open(file_name);
    medicine_file >> 
med_name>>med_formula>>med_weight>>med_price>>med_company>>expiry_date;
    medicine_file.close();
}

void Medicine::createFile()
{


    medicine_file.open(file_name);
    if (!medicine_file.is_open())
        std::cout << "file is not opening\n";
    medicine_file.close();
}

void Medicine::setFileName(std::string &recieved)
{
    file_name = recieved;
}

这是 MedClass.h :-

#pragma once
#include <string>
#include <iostream> 
#include <fstream>
#include <limits>

class Medicine
{
public :

    std::string getFileName();
    std::string getMedicineName();
    std::string getMedicineFormula();
    void displayMedInfo();
    int getMedUnitsLeft();
    void writeToFile();
    void getFromFile();
    void createFile();
    void setFileName(std::string &recieved);


private:

    std::fstream medicine_file;

    std::string file_name;
    std::string file_input;
    std::string med_name;
    std::string med_formula;
    std::string expiry_date;
    std::string med_company;
    float med_weight;
    float med_price;
    int med_units_left;
};

现在，如果我以这种方式在 main.cpp 中实现它：-

void ViewMedicine()
{
    Medicine med;
    std::string medicine_name;
    std::string medicine_filename;
    std::cout << "Enter medicine name to view : \n";
    getline(std::cin, medicine_name);
    medicine_filename = "Medicines\\" + medicine_name + ".txt";
    std::ifstream check_med_by_name;
    check_med_by_name.open(medicine_filename);
    if (!check_med_by_name.is_open())
    {
        std::cout << "Medicine not found\n";

    }
    else
    {
        med.setFileName(medicine_filename);
        med.getFromFile();
        med.displayMedInfo();
        check_med_by_name.close();
    }
}
int main()
{
    std::string medicine_name;
    std::string medicine_filename;
    Medicine medic;
    std::cout<<"View Existing Medicines \n";
    ViewMedicines();
    std::cout<<"Enter the name of medicine to add : \n";
    getline(std::cin,medicine_name);

    medicine_filename = "Medicines\\" + medicine_name + ".txt";
    medic.setFileName(medicine_filename);
    medic.createFile();
    medic.writeToFile();
    return 0;
}

如果程序运行正确，它应该在药品文件夹中创建一个文件，并且不应该在输出中显示“文件未打开”。但是我得到“文件未打开”作为程序输出。这表明文件未创建。即使手动创建药物文件夹也无济于事。

但我可以在医学文件夹中查看已经存在的手动创建的名为 med 的医学文件。

程序输出是这样的：-

View existing medicines
Enter medicine name to view :
med
Details of selected medicine :

Medicine name :- name
Medicine formula :- formula
Medicine weight :- 50
Medicine Price :- 100
Medicine Expire Date :- 10/04/21
Medicine Company :- company


Enter the name of medicine to add :
new
file is not opening
Enter details of medicine in following format :-
Name Formula Weight Price Company Expiry
new new 50 100 new 0
file input validated
press any key to continue...

那么为什么我能够查看已经存在的药物文件，但不能使用成员函数 CreateFile() 创建一个新的？我应该怎么做才能创建一个包含所有详细信息的新药物文件，以便我以后可以访问它.

Answer 1

1) 默认fstream 模式不会创建新文件。

`std::fstream medicine_filename;
 ...
 medicine_file.open()'

open() 不会创建新文件，因为默认模式是in | out。要先创建文件，您只需指定out 模式即可。

2) 药物文件名 = "药物\" + 药物名称 + ".txt"；

检查“Medicines”目录是否存在。要进行测试，请尝试使用驱动器形成完整路径，例如“C:\\Temp\\test.txt”。

Answer 2

好吧，看来我已经解决了。如果我在 createFile() 函数中添加一个小改动，程序就会完美运行。

void Medicine::createFile()
{


    std::ofstream medicine_file(file_name);
    if (!medicine_file.is_open())
        std::cout << "file is not opening\n";
    medicine_file.close();
}

我将第一行从“medicine_file.open(file_name)”更改为“std::ofstream Medicine_file(file_name)”，它按预期运行。