Using caller information for verbose logging

#csharp #compilerservices #diagnostics

A cool feature that has been added in Visual Studio 2012 and C# 5.0 is Caller Information attributes. Basically it allows you to see where your method was called from without having to sift through stack traces upon stack traces.

You simply prefix an optional parameter with one of the three attributes:

[CallerMemberName] provides the method or property name of the caller as a string.

[CallerFilePath] provides the full path of the source file that contains the caller as a string.

[CallerLineNumber] provides the line number in the source file at which the method is called as an int.

Learn by example. Here I've made a simple logging method, we pass to it a string, and the compiler will fill in the rest. Make sure to including System.Runtime.CompilerServices in your using statements.

static void VerboseLog(string value,
    [CallerMemberName] string callerMemberName = "",
    [CallerFilePath] string callerFilePath = "",
    [CallerLineNumber] int callerLineNumber = -1)
{
    int index = callerFilePath.LastIndexOf(Path.DirectorySeparatorChar);
    string localPath = callerFilePath.Substring(index + 1);
    Debug.WriteLine("{0} {1}:{2} {3}",
        localPath, callerMemberName, callerLineNumber, value);
}

Let's test it with a simple Console Application. Notice in the above method that I remove the full path to make it more readable. Not necessarily needed but pleasant nonetheless.

static void Main(string[] args)
{
    VerboseLog("this is a test");
    DoSomething();
}

static void DoSomething()
{
    for (int i = 0; i < 5; i++)
    {
        VerboseLog(string.Format("something {0}", i));
    }
}

This outputs:

Program.cs Main:16 this is a test
Program.cs DoSomething:24 something 0
Program.cs DoSomething:24 something 1
Program.cs DoSomething:24 something 2
Program.cs DoSomething:24 something 3
Program.cs DoSomething:24 something 4

So very simple, and yet very, very useful.