For logging purposes
__LINE__
__FILE__
were my friends in C/C++. In Java to get that information I had to throw an exception and catch it. Why are these old standbys so neglected in the modern programming languages? There is something magical about their simplicity.
Caller Information has been added to .NET 4.5. This will be compiled, a big improvement over having to examine the stack trace manually.
public void Log(string message,
[CallerFilePath] string filePath = "",
[CallerLineNumber] int lineNumber = 0)
{
// Do logging
}
Simply call it in this manner. The compiler will fill in the file name and line number for you:
logger.Log("Hello!");
It is uglier, but you can do something like this in C# using the StackTrace and StackFrame classes:
StackTrace st = new StackTrace(new StackFrame(true));
Console.WriteLine(" Stack trace for current level: {0}", st.ToString());
StackFrame sf = st.GetFrame(0);
Console.WriteLine(" File: {0}", sf.GetFileName());
Console.WriteLine(" Method: {0}", sf.GetMethod().Name);
Console.WriteLine(" Line Number: {0}", sf.GetFileLineNumber());
Console.WriteLine(" Column Number: {0}", sf.GetFileColumnNumber());
Of course, this comes with some overhead.
With Caller Information (introduced in .NET 4.5) you can create the equivalent of __LINE__ and __FILE__ in C#:
static int __LINE__([System.Runtime.CompilerServices.CallerLineNumber] int lineNumber = 0)
{
return lineNumber;
}
static string __FILE__([System.Runtime.CompilerServices.CallerFilePath] string fileName = "")
{
return fileName;
}
The only thing to remember is that these are functions and not compiler directives.
So for example:
MessageBox.Show("Line " + __LINE__() + " in " + __FILE__());
If you were to use this in practise then I'd suggest different names. I've used the C/C++ names just to make it clearer what they are returning, and something like CurrentLineNumber() and CurrentFileName() might be better names.
The advantage of using Caller Information over any solution that uses the StackTrace is that the line and file information is available for both debug and release.
The closest thing to those is the fact that you can create a StackTrace object and find out the name of the method at the top of the stack, so you can get close to the functionality of the __FUNCTION__ macro.
StackTrace stackTrace = new StackTrace();
StackFrame[] stackFrames = stackTrace.GetFrames();
foreach (StackFrame stackFrame in stackFrames)
Console.WriteLine(stackFrame.GetMethod().Name);
To reduce the cost of typing this out by hand, and also the runtime code, you can write a helper method:
[Conditional("Debug")]
public void LogMethodName()
{
Trace.WriteLine("Entering:" + new StackTrace().GetFrame(1).GetMethod().Name);
}
Note how we get frame 1, as frame 0 would be LogMethodName itself. By marking it as Conditional("Debug") we ensure that the code is removed from release builds, which is one way to avoid the runtime cost where it may not be needed.
Because the stack trace contains most of what you need. It will not give you the name of the file but it will give you the class/method name. It also contains the line number. It is not neglected it is automatic. You just need to throw an exception like you do it in Java
Here's a way to get the line number: http://askville.amazon.com/SimilarQuestions.do?req=line-numbers-stored-stack-trace-C%2523-application-throws-exception
If you use log4net, you can get the line number and file name in your logs, but:
Having used the FILE and LINE macros for many years for logging in C/C++ I really wanted a similar solution in C#. This is my solution. I prefer it to @fostandy suggestion of creating many overloads with varying number of parameters. This seems the less intrusive and does not limit the number of formatted parameters. You just have to be willing to accept the addition of the F.L() parameter at start of every Log.Msg() call.
using System;
using System.Runtime.CompilerServices;
namespace LogFileLine
{
public static class F
{
// This method returns the callers filename and line number
public static string L([CallerFilePath] string file = "", [CallerLineNumber] int line = 0)
{
// Remove path leaving only filename
while (file.IndexOf("\\") >= 0)
file = file.Substring(file.IndexOf("\\")+1);
return String.Format("{0} {1}:", file, line);
}
}
public static class Log
{
// Log a formatted message. Filename and line number of location of call
// to Msg method is automatically appended to start of formatted message.
// Must be called with this syntax:
// Log.Msg(F.L(), "Format using {0} {1} etc", ...);
public static void Msg(string fileLine, string format, params object[] parms)
{
string message = String.Format(format, parms);
Console.WriteLine("{0} {1}", fileLine, message);
}
}
class Program
{
static void Main(string[] args)
{
int six = 6;
string nine = "nine";
string dog = "dog";
string cat = "cats";
Log.Msg(F.L(), "The {0} chased the {1} {2}", dog, 5, cat);
Log.Msg(F.L(), "Message with no parameters");
Log.Msg(F.L(), "Message with 8 parameters {0} {1} {2} {3} {4} {5} {6} {7}",
1, 2, 3, "four", 5, 6, 7, 8.0);
Log.Msg(F.L(), "This is a message with params {0} and {1}", six, nine);
}
}
}
Here's the output from this code above
Program.cs 41: The dog chased the 5 cats
Program.cs 43: Message with no parameters
Program.cs 45: Message with 8 parameters 1 2 3 four 5 6 7 8
Program.cs 48: This is a message with params 6 and nine
There are already some suggestions to achieve what you want. Either use the StackTrace object or better log4net.
In Java to get that information I had to throw an exception and catch it.
That's not quite true. You can have it without throwing exceptions, too. Have a look to log4j. It even logs your method and class name, without polluting your code with hard coded strings containing the current method name (at least I have seen this in some occasions).
Why are these old standbys so neglected in the modern programming languages?
Java and C# don't make use (in the latter: excessive use) of preprocessors. And I think it's good. Abusing preprocessors to make unreadable code is very easy. And if programmers can abuse some technique ... they will abuse it.
Just a note about performance, which is very likely to be the next thing, which pops up in your mind:
If you use StackTrace or log4net you will always will read or hear that it is slow, because it uses Reflection. I am using log4net and I never encountered logging as a performance bottle neck. If it would be, I can declaratively deactivate (parts of) logging -- without changing the source code. That's pure beauty compared to delete all the logging lines in C/C++ code! (Besides: If performance is a primary goal, I would use C/C++ ... it will never die despite of Java and C#.)
