Strange problem

Question

Strange problem

I have a really weird problem. In Visual C ++ express, I have very simple code, just:

#include <fstream>
using namespace std;
int main()
{
fstream file;
file.open("test.txt");
file<<"Hello";
file.close();
}

This same code works fine in my one project, but when I create a project and use these same lines of code, no test.txt file is generated. Please, what's wrong? ¨

EDIT: I expect to see test.txt in VS2008 / project_name / debug - just like the first functional project does.

+2

c ++ fstream

noname May 09 '10 at 19:26

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5 answers

anon · Answer 1 · 2010-05-09T21:27:14+0000

Canonical code to write to file:

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

int main() {
    ofstream file;
    file.open("test.txt");
    if ( ! file.is_open() ) {
       cerr << "open error\n";
    }

    if ( ! (  file << "Hello" ) ) {
       cerr << "write error\n";
    }

   file.close();

}

Whenever you do file I / O, you should check every operation, except perhaps closing a file, which is usually impossible to recover from.

As for a file created somewhere else, just give it a weird name, for example mxyzptlk.txt

, and then find it using Windows Explorer.

Joey adams · Answer 2 · 2010-05-09T19:31:28+0000

Perhaps the executable is being run in a different directory than before, causing test.txt to appear somewhere else. Try using an absolute path like "C:\\Users\\NoName\\Desktop\\test.txt"

(double backslashes are needed as escape characters in C strings).

Johnsyweb · Answer 3 · 2010-05-09T20:56:51+0000

fstream::open()

takes two arguments: filename

and mode

. Since you do not provide the latter, you can check that the default argument fstream

is present or provide it ios_base::out

yourself.

Also, you can check if the file is open. You may not have write permissions in the current working directory (where "test.txt" will be written because you do not provide an absolute path). fstream

provides a method is_open()

as one way to test this.

Finally, consider deviating from your code. While you only have a few lines, the code can soon become difficult to read without proper indentation. Sample code:

#include <fstream>
using namespace std;
int main()
{
    fstream file;
    file.open("test.txt", ios_base::out);
    if (not file.is_open())
    {
        // Your error-handling code here
    }
    file << "Hello";
    file.close();
}

Chris Schmich · Answer 4 · 2010-05-09T21:30:54+0000

You can use Process Monitor and filter file access and your process to determine if open / write is in progress and where on disk it is.

Kevin · Answer 5 · 2014-12-21T21:47:02+0000

There are two ways to fix this. Or do:

file.open ("test.txt", ios :: out)

#include <fstream>

using namespace std;

int main()
{
    fstream file;
    file.open("test.txt", ios::out);
    file<<"Hello";
    file.close();
}

Or you can create stream from stream instead of fstream.

#include <fstream>

using namespace std;

int main()
{
    ofstream file;
    file.open("test.txt");
    file<<"Hello";
    file.close();
}

Strange problem

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