Question

I would like to print out my debug message with line number in VB.net application.
I did like this,

Dim st As StackTrace
Dim sf As StackFramee
st = New StackTrace(New StackFrame(True))
sf = st.GetFrame(0)
Console.WriteLine.("Line " & sf.GetFileLineNumber()）

I wanna put the snippet to a class, everytime I call logMsg method to log my message with line number in source code.
But I found if I put the snippet above into a class, the line number was always same, that’s the line which I new ‘st’.

The function is exact same with _LINE macro in C++. Actually I am C++ programmer.

Anyway to fix this problem? thanks.

Answer 1

The code you’ve shown is working exactly as expected. It’s printing the number of the line where you captured the stack frame. Because you’ve defined it in a different class, it’s printing the line number of the file that contains that class.

The GetFrame method is important here. Stack frames are numbered starting at 0, which is the last stack frame pushed. So, by referring to frame 0, you are instructing the runtime to print the line number of the last stack frame that was pushed. When one method calls another, a new stack frame is created.

Instead, you need to change your method in a couple of important ways. First, you need to get the first frame that was pushed onto the stack. And second, you probably want to accept a parameter containing information about the exception that you are responding to. Try rewriting your debug method to look something like this:

Public Sub PrintCurrentLine(ByVal ex As Exception)
    Dim st As StackTrace = New StackTrace(ex)
    Dim sf As StackFrame = st.GetFrame(st.FrameCount - 1)
    Console.WriteLine("Line " & sf.GetFileLineNumber())
End Sub

Also remember that if you’re running the code with optimizations enabled, things like line numbers may have changed. You always need to include the PDB file with your code, which contains debugging information that is used in situations like this. It maps the optimized code back to your original source.