c++ ofstream doesn't modify files. Even the tutorial examples

July 30, 2022

I am writing a program that needs to read from one file and write to another. Using fstream, I implemented the reading part, but the writing part didn’t work no matter what I tried.

I tried the ‘example programs’ from all sorts of websites, but none of them worked. I tried changing things like file.isOpen() == false to !file and all that, but still nothing.

It doesn’t matter if file exists or not, ofstream functions just don’t seem to work.

From what I read, it seems to be a permissions issue? Besides that, I have no other clue. There are no errors or abnormal statuses reported. Everything before and after works fine while ofstream functions are just ignored.

I am using Visual Studio Code, windows 10. Snippet from w3schools I tried.

#include <iostream>
#include <fstream>
using namespace std;

int main() {
    // Create and open a text file
    ofstream MyFile("filename.txt");

    // Write to the file
    MyFile << "Files can be tricky, but it is fun enough!";

    // Close the file
    MyFile.close();
}

>Solution :

@timebender

I tried following code using g++.exe(cygwin windows)

    #include <string.h>
    #include <sys/errno.h>
    #include <iostream>
    #include <fstream>
    using namespace std;
    int main()
    {
     // Create and open a text file
     ofstream MyFile("filename.txt", ios::app|ios::out);
     if ( MyFile.is_open() )
     {
            cout << "is_open pass\n";
            // Write to the file
            MyFile << "Files can be tricky, but it is fun enough!\n";
            // Close the file
            MyFile.close();
            cout << "closed file\n";
     }
     else
     {
            cout << "ofstream filename.txt failed\n";
            cout << strerror(errno) << "\n";
     }
     return 0;
    }
    $ g++ 73174678.cpp -o ./a.out;a.out
    $ ./a.out
    is_open pass
    closed file
    $ cat "filename.txt"
    Files can be tricky, but it is fun enough!
    $ g++.exe 73174678.cpp -o ./a.exe;./a.exe
    $ ./a.exe
    is_open pass
    closed file