无法在C ++中打开文件

Question

What mistake am I doing that the file is not opening. The output screen shows file could not be opened. If I separately create ofstream and ifstream constructors than the file is written and read correctly. If I use fstream as below the file is not being created.

#include <iostream>
#include <fstream>
using namespace std;
void main(){

    char num[10];
    fstream file;
    file.open("text.txt", ios::ate|ios::in|ios::out| ios::binary);
    if (!file)
    {
        cerr << "File could not be opened" << endl;
        exit(1);
    } // End if

    for (int i = 0; i <= 5; i++){
        cout << "Enter an integer " << endl;
        cin >> num[i];        //Input a number
        file.write((char*)num, sizeof(num));  //Function write to write data to file
    }

    for (int i = 0; i <= 5; i++){
        file.read((char*)num, sizeof(num));  //Function to read data from the file
        cout << endl << num[i] << " ";
    }
    file.close();
    system("pause");
}

Answer 1

You should specify ios::trunc or ios::app depending on whether you want the file to be rewritten or appended to, otherwise it won't be created if it doesn't exist:

file.open("text.txt", ios::trunc | ios::in | ios::out | ios::binary);

Note that ios::ate doesn't make sense in combination with ios::trunc because the file is truncated.

You may also take a look at the table of correspondence between ios flags and equivalent stdio mode strings . As you can see, the corresponding line of the table for your current code is

modestring openmode & ~ate  Action if file already exists   Action if file does not exist
"r+b"       binary|out|in        Read from start            Error

PS: And don't forget to change void main() to int main() because the former is undefined behavior.

Update: and yes, your whole writing and reading code is wrong. It should be rewritten as follows:

for (int i = 0; i <= 5; i++){
    cout << "Enter an integer " << endl;
    cin >> num[i];        //Input a number
}
// write the array once and outside of the loop
file.write((char*)num, sizeof(num)); 

// not necessary - just to ensure we read numbers in the next lines
memset(num, 0, sizeof(num)); 
// go to the beginning of the file
file.seekg(0);
// read the array once and outside of the loop
file.read((char*)num, sizeof(num));

for (int i = 0; i <= 5; i++){
    cout << endl << num[i] << " ";
}

DEMO

Answer 2

You should add 'ios::out' to your file.open

file.open("text.txt", ios::out);

You can also check if the file was opened easier by using

if (!file.is_open())

EDIT:

Probably the combination is not valid. Try to use

file.open("text.txt", ios::app|ios::out|ios::in|ios::binary);

instead