Question

I’m trying to define custom file parse exception class, which to holds information – the name of the file and the line of the file on which the exception is happening.

class FileParseException : Exception {
    string fileName;
    long lineNumber;
    public FileParseException() {
    }
    public string GetFileName() {
        return fileName;
    }
    public long GetLineNumber() {
        return lineNumber;
    }
}

How should I store the data for the current file and when it rises an exception to access it through thy-catch block:

try {
    // some code here
}
catch (FileParseException fpe) {
    Console.WriteLine(fpe.getLineNumber);
}

Answer 1

First, C# has properties, so you should use them, not create GetXXX methods. In your case, public automatic properties with private setters should do the job:

public string FileName { get; private set; }
public long LineNumber { get; private set; }

You can set them in a constructor of the exception:

public FileParseException(string fileName, long lineNumber)
{
    FileName = fileName;
    LineNumber = lineNumber;
}

To throw such exception, use the constructor above:

throw new FileParseException(fileName, lineNumber);

And when you catch it, you can access the properties:

catch (FileParseException fpe)
{
    Console.WriteLine(
        "Error in file {0} on line {1}.", fpe.FileName, fpe.LineNumber);
}

Also, you should probably set the Message of the exception, by passing the message to the base constructor:

public FileParseException(string fileName, long lineNumber)
    : base(
        string.Format(
            "Error while parsing file {0} on line {1}.", fileName, lineNumber))
{
    FileName = fileName;
    LineNumber = lineNumber;
}