StreamWriter doesn't write to a file that doesn't exist

Question

I am making a level editor for my game, and most of it is working except... When I try to save my file (XML) the file doesn't get created, and in the output box I get:

A first chance exception of type 'System.NullReferenceException'

The funny thing is that it only happens if the file doesn't exist, but it works correctly if I overwrite another file.

here is the code I'm using:

using (StreamWriter stream = new StreamWriter(filePath))
{
    stream.Write(data);
    stream.Close();
}

data is a string (this is not the problem because it works when I overwrite the file)

Solution 1

You're missing a constructor which takes a boolean that can aid in creating the file:

using (StreamWriter stream = new StreamWriter(filePath, false)) {
    stream.Write(data);
    stream.Close();
}

The logic is actually is little more complex than that, however:

public StreamWriter( string path, bool append )

Determines whether data is to be appended to the file. If the file exists and append is false, the file is overwritten. If the file exists and append is true, the data is appended to the file. Otherwise, a new file is created.

Solution 2

Why don't you just go around it the easy way, and check for file existence prior to writing to it:

public void Foo(string path, string data)
{
    if (!File.Exists(path))
        File.Create(path);

        using (var sw = new StreamWriter(path, false))
        {
            // Work your magic.
            sw.Write();
        }
}

I'd really not make it any more complicated than that personally. Also, don't close the StreamWriter, the using statement disposes of it after it's served its purpose.

Solution 3

In my case I was running the program as non-admin, the file was to be written inside a folder that was created with administrator rights (even inside ProgramFiles or any non-admin location). The file is never created and you have to manually enable the Managed Debugging Assistants exception breaks in order to see any error.

Solution was to delete the folder and create it again with my non-admin account. Also note that StreamWriter does not create directory trees, only files.

Comments

[ChrisF]

Which line gives the NullReferenceException?

[annonymously]

It doesn't say, I think the StreamWriter must catch the exception and Debug.WriteLine the message

[ChrisF]

The only thing I can think of is that the program doesn't have create permissions to the directory. Try removing the using (for debug purposes only) and see if you get a more meaningful exception.

[annonymously]

@ChrisF nope, the exception is still not appearing, it's just being written to the output box

[annonymously]

@luisperezphd yes, they work if the file exists

[annonymously]

@ChrisF when I set a breakpoint on the line where I set data and step over to the StreamWriter part it just resumes my program.

[Jim Mischel]

I strongly suspect that there's something else in your code that's crashing before you get to the StreamWriter here. Or, perhaps filePath is null if the file doesn't already exist? On a separate note, there's no reason to call stream.Close() if you're in a using. That'll be done for you automatically.

[annonymously]

@JimMischel The breakpoints work right up to the line where I create the StreamWriter. filePath is not null and I have removed the using part as it was only for debugging

[annonymously]

Yes, that was the first way that worked and I copy pasted my backup sorry ;)

[annonymously]

Well, that makes the stream append to the file, I want to replace the file

[annonymously]

If the file exists I want to overwrite it, not append to it

[ChrisF]

I don't think this is the correct overload. The problem is not that the file is getting overwritten, but that it's not getting created in the first place.

[Grant Thomas]

@ChrisF I've taken a look and with append being false this constructor will always create the file if it doesn't exist. As per this: Initializes a new instance of the StreamWriter class for the specified file on the specified path, using the default encoding and buffer size. If the file exists, it can be either overwritten or appended to. If the file does not exist, this constructor creates a new file.

[aevitas]

When using the using keyword, you don't need to call sw.Close(), it's taken care of automatically. (which is the whole point of using using in the first place)

[Luis Perez]

When I run this code it creates a file if it doesn't exist. And overwrites it does exist - is that not the behavior you wanted?

[Luis Perez]

Ok, I see, this is the way it should behave, but it's not working on your specific computer. Can you get a stack trace? Have you tried to see if you have the latest version of the .NET framework? Maybe somehow you have write but not create permission to the folder?

[annonymously]

@aevitas Actually I only used the using part for debugging to see if it would work

[annonymously]

I do have the latest .net framework, and I'm pretty sure I have create permissions to the folder. As for the stack trace, I'm sorry but I can't seem to debug after the error, it just resumes the program

[Luis Perez]

You can try running the free filemon application to see if it gives you any more details. There is also a setting in visual studio that will freeze the application when any exception is thrown even handled ones. Finally you can add code to output the stack trace.

[Grant Thomas]

The check is redundant though, so inherently makes things more complex.

[aevitas]

Personally I don't think it does. Even though it may be redundant, it makes it easier to read, understand, and debug.

[xmedeko]

It's not easier to read. What this code says about race conditions? What if other process deletes the file just after it's created? It error prone to race conditions. StreamWriter has to correctly create the file. Otherwise it's a bug in .NET.