Logging That Doesn't Suck

2/4/26

Sometimes you don't want to log something and you'd rather just plaster a return nullptr or return; somewhere you might have loved to have a log, but the issue is you'll spend 10 minutes writing the log statement because every statement seems to come with a complimentary google session for "how the fuck do I get my boolean to print in a log statement"

Let's talk about UE_LOG

I'm not really a fan of logging using Unreal's most common macro, UE_LOG. It's also entirely possible I've shown up when a better tool is finally here to use, but the biggest issue I have is essentially the fact that when using UE_LOG, I have to know what format specifier to use.

Format specifier, yeah. It's that weird... uh. Percentage thing.

It's actually pretty terrible, there are at least good resources that can help you understand which format specifier to go for, but just for a refresher:

Specifier	What it decodes
%s	FString
%d	int
%f	float
%s	FVector

This isn't complete, but like. It's a pain in the ass? I don't want to remember five to seven different specifiers based on whatever type I'm using.

UE_LOG(LogTemp, Warning, TEXT("The integer value is: %d"), 1);

Like. Really? You're telling me %d is meant for numbers? I guess you could say "digit" is what it stands for here. but I don't want to guess. So I won't. Let's talk about a cooler way to log.

Let's talk about UE_LOGFMT

As of Unreal 5.2, you can log in a VERY nice way that handles a lot of that formatting for you. Most of what you worry about is how to get a type that isn't easily serialized into a string to become a string. If we take the example above using UE_LOGFMT, we get this:

INFO

Again, this is UNREAL 5.2 AND ONWARD. Oh god who cares there's no reason you're running early 5.0 unless you're about to ship a game.

/** Using positional arguments, too! */
UE_LOGFMT(LogTemp, Warning, "The integer value is: {v}", 1);

This macro automatically supports converting the type you provide it to the right format, and using positional arguments, you can pepper it with all sorts of useful information!

My favorite way to log

My favorite way to log is to log with a lot of information. but the fact that this exists makes logging something I want to do a lot more these days.

UE_LOGFMT(
    LogTemp,
    Warning,
    "{fn}: This is a warning, you gave me a bad UObject! ({u})",
    __func__,
    IsValid(SomeObject) ? SomeObject->GetName() : "NONE"
);

Lo and behold! Let's break this down:

1. I'm using UE_LOGFMT with positional arguments. You can use named arguments where the order won't matter, but I like positional parameters.
2. I'm using __func__! This isn't an unreal thing, this is a C++ thing that returns the name of the currently executing function and I LOVE IT.

UE_LOGFMT works well with FString, float, int, UObject with GetName and any FName with GetName. Basically anything that can return a serializable string version of itself will end up working!

Caveats

I haven't really tried this with larger structs, but as long as you implement a ToString function or something similar, or even use some utilities the engine offers, you can probably convert the value of a struct to a string pretty straightforwardly!

Final thoughts

I have never really deviated from using UE_LOGFMT and I've never gone back to UE_LOG. It's just not worth it. Don't spend your time figuring out how to log an FVector. Get on with your life. Write meaningful code, and log shit when things go wrong.