CODEWITHSUNDEEP
c++filefile-iofstreamifstream
Joshua LI
Joshua LI

Reputation: 4733

"File could not be opened." C++ fstream

Code : 

int question_3()
{
    fstream hardware("hardware.dat" , ios::binary | ios::in | ios::out);

    if (!hardware)
    {
        cerr << "File could not be opened." << endl;
        exit(1);
    }

    HardwareData myHardwareData;

    for (int counter = 1; counter <= 100; counter++)
    {
        hardware.write(reinterpret_cast< const char * >(&myHardwareData), sizeof(HardwareData));
    }

    cout << "Successfully create 100 blank objects and write them into the file." << endl;
.
.
.

Result :

enter image description here

Why the file could not be opened?

If the file "hardware.dat" do not exist, the program will create the file with that name. Why not?

If I first create the file like the following, the program will continue.

![enter image description here][2]

Thank you for your attention.

Final Solution : 

int question_3()
{
    cout << "Question 2" << endl;

    fstream hardware;                                         <---Changed
    hardware.open("hardware.dat" , ios::binary | ios::out);   <---Changed

    if (!hardware)
    {
        cerr << "File could not be opened." << endl;
        exit(1);
    }

    HardwareData myHardwareData;

    for (int counter = 1; counter <= 100; counter++)
    {
        hardware.write(reinterpret_cast< const char * >(&myHardwareData), sizeof(HardwareData));
    }

    cout << "Successfully create 100 blank objects and write them into the file." << endl;

    hardware.close();                                                   <---Changed
    hardware.open("hardware.dat" , ios::binary | ios::out | ios::in);   <---Changed
.
.
.

enter image description here

Upvotes: 1

Views: 3485

Answers (3)

Pandrei
Pandrei

Reputation: 4951

the ios::in specifies you want to open an existing file for reading. Since you don't seam want to read anything you shoul jsut stick to ios::out which will create the file if it does not exist and open it for writing.

Upvotes: 1

Nemanja Boric
Nemanja Boric

Reputation: 22157

Why are you opening your file with both ios::in and ios::out flags (it seems that you're only writing to this file)? ios::in will require an existing file:

#include <fstream>
#include <iostream>
using namespace std;
int main()
{
    fstream f1("test1.out", ios::binary | ios::in | ios::out);
    if(!f1)
    {
        cout << "test1 failed\n";
    }
    else
    {
        cout << "test1 succeded\n";
    }


    fstream f2("test2.out", ios::binary | ios::out);
    if(!f2)
    {
        cout << "test 2 failed\n";
    }
    else
    {
        cout << "test2 succeded\n";
    }
}

output:

burgos@olivia ~/Desktop/test $ ./a.out 
test1 failed
test2 succeded

Maybe you want to use ios::app?

Upvotes: 3

molbdnilo
molbdnilo

Reputation: 66371

When you specify both ios::in and ios::out, the file must exist - it will not be created.

If you're just writing, use only ios::out.

Upvotes: 1

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