This plugin was developed to have a unified way for logging that can be used in shipping builds.

This should be all the documentation you need to use the Universal Logging library

In the simplest case, you can just do:

#include "IUniversalLogging.h"

...

UniLog.Log("Message");

This will log Message to <your project dir>/Saved/Logs/UniversalLogging.log.

There are other levels of control, though:

UniLog.Log("Message", "Name");

UniLog.Log("Message", "Name", true);

This will log Message to <your project dir>/Saved/Logs/UniversalLogging_Name.log and in the latter case will omit the newline which would otherwise be automatically added.

UniversalLogging is also available from blueprints. Look for the Log, NewLogStream and ModifyLogStream nodes.

The LogF function allows you to log using a printf-like syntax. The only thing to keep in mind is that FString variables have to be passed as pointers.

FString variable = "Hello!";
UniLog.LogF("Name", "Message %s", *variable);

Note that the LogF function does not automatically add a newline at the end.

You might not want to have more control over your logs and, e.g., set where they are saved. Settings are provided through LogStream objects. Create them like this:

ILogStream* stream = UniLog.NewLogStream(StreamName, PathToFile, Filename, PerSession, LogOnMaster, LogOnSlaves);

Parameters:

• StreamName (FString): The name of the newly created LogStream which will be used as a handle to retrieve it in the future.
• PathToFile (FString): The path where you want your log(s) to be saved, relative to the project path. (Empty string for project root)
• Filename (FString): The name of the log file. You have to specify a file extension.
• PerSession (bool): If false (default) the log is overwritten each time the application is started. If true, a new folder is created at every launch, so the file is saved in <Project Path>/<PathToFile>/<SessionID>/<Filename>.
• LogOnMaster (bool): For cluster mode (e.g. for the aixCAVE), specify if the master node writes the log (default) or not.
• LogOnSlaves (bool): For cluster mode (e.g. for the aixCAVE), specify if the slave nodes write the log or not (default). The log file will be located in <Project Path>/<PathToFile>/slavelogs/<Slave ID>_<Filename>.

The path provided is still relative to your project directory. As soon as you created the LogStream, the complete filepath and the file are attempted to be created. You can check if it was successful using:

ILogStream* stream = UniLog.GetLogStream("StreamName");
if (stream->GetIsValid()) {...}

After your stream was created, you can log to it like before using "StreamName" to identify it:

UniLog.Log("Message", "StreamName");
UniLog.LogF("StreamName", "Message %s", *variable);

You can simply specify the same file name and file path in multiple LogStreams. The output of both streams will be written to this file. This can be useful to have separate streams for errors or warnings. To distinguish the streams, you can use

stream->SetPrefix("Warning: "); // No additional space will be added after the prefix, so make sure to add one if you want that

to set a prefix that will automatically be added to every message that is written to the file (this will not show up in the on screen log).

You can also display the log messages on screen. This can even be enabled/disabled during runtime. To do this, use the ILogStream interface:

ILogStream* stream = UniLog.GetLogStream("StreamName");
stream->SetOnScreen(true);

You can also change the color of the messages, to distinguish multiple streams that are logging to the screen at the same time:

stream->SetOnScreenColor(FColor(255, 0, 255, 255)); // FColor parameters are int8 RGBA

By default, the on screen messages are only shown on the master in cluster mode. You can change this behavior using:

stream->SetLogOnScreenOnMaster(false);
stream->SetLogOnScreenOnSlaves(true);

You might want to have log files that don't get overwritten each time your application starts. You can specify this when creating the LogStream:

UniLog.NewLogStream("StreamName", "path/to/file", "filename.log", true);

This will put a session identifier folder between the path and the filename. A session starts with every run of the application (like clicking "Play" in the editor).

The SessionID is automatically generated at the start of each session. You may access it using:

FString SessionID = UniLog.GetSessionIdentifier();

Usually, it is of the form: <Play|PlayInPreview|PlayInEditor|Stopped>_MM-DD-YY_hh-mm-ss. However, it can be changed using the command line argument -SessionID=<Custom ID>. If this argument is present, it is always used. This is used for the aixCAVE, since the SessionID will not be the same on all slaves otherwise.