FileInfo.Length大于0但文件是否为空？

Question

I have an application that crunches a bunch of text files. Currently, I have code like this (snipped-together excerpt):

FileInfo info = new FileInfo(...)
if (info.Length > 0) {
    string content = getFileContents(...);
        // uses a StreamReader
        // returns reader.ReadToEnd();
    Debug.Assert(!string.IsNullOrEmpty(contents)); // FAIL
}

private string getFileContents(string filename)
    {
        TextReader reader = null;
        string text = "";

        try
        {
            reader = new StreamReader(filename);
            text = reader.ReadToEnd();
        }
        catch (IOException e)
        {
            // File is concurrently accessed. Come back later.
            text = "";
        }
        finally
        {
            if (reader != null)
            {
                reader.Close();
            }
        }

        return text;
    }

Why am I getting a failed assert? The FileInfo.Length attribute was already used to validate that the file is non-empty.

Edit: This appears to be a bug -- I'm catching IO exceptions and returning empty-string. But, because of the discussion around fileInfo.Length(), here's something interesting: fileInfo.Length returns 2 for an empty, only-BOM-marker text file (created in Notepad).

Answer 1

You might have a file which is empty apart from a byte-order mark. I think TextReader.ReadToEnd() would remove the byte-order mark, giving you an empty string.

Alternatively, the file could have been truncated between checking the length and reading it.

For diagnostic purposes, I suggest you log the file length when you get an empty string.

Answer 2

See that catch (IOException) block you have? That's what returns an empty string and triggers the assert even when the file is not empty.

Answer 3

If I remember well, a file ends with end of file, which won't be included when you call ReadToEnd.

Therefore, the file size is not 0, but it's content size is.

Answer 4

What's in the getFileContents method?

It may be repositioning the stream's pointer to the end of the stream before ReadToEnd() is called.