How to print strings to console or screen in Unreal Engine C++ at runtime. The Unreal Blog

There are many reasons why this may be needed: for example, for debugging or testing code execution.

How to print messages to console

We can define a custom log:

DECLARE_LOG_CATEGORY_EXTERN(LogNameExample, Log, All);

If you decide to use a custom log, just replace "LogTemp" from the examples below with the name of your log ("LogNameExample" from the example above)

Simple message:

UE_LOG(LogTemp, Warning, TEXT("Message example"));

String message:

FString StringExample = TEXT("String example");
UE_LOG(LogTemp, Warning, TEXT("Output: %s"), *StringExample);

Int message:

int32 IntegerExample = 4; // you can use int8, uint8, int16, uint16, int32, uint32, int64, uint64 to log this way
UE_LOG(LogTemp, Warning, TEXT("Output: %d"), IntegerExample);

Float message:

float FloatExample = 10.4;
UE_LOG(LogTemp, Warning, TEXT("Output: %f"), FloatExample);

FVector message:

FVector VectorExample = FVector(100, 200, 300);
UE_LOG(LogTemp, Warning, TEXT("Output: %s"), *VectorExample.ToString());

FName message:

FName NameExample = FName("Name example")
UE_LOG(LogTemp, Warning, TEXT("Output: %s"), *NameExample.ToString());

How to print messages to screen

For everything to work well, you need to include "EngineGlobals.h" in the declaration (.h) file:

#include "Runtime/Engine/Public/EngineGlobals.h"

Simple message:

GEngine->AddOnScreenDebugMessage(-1, 12.f, FColor::White, TEXT("Simple message"));

Custom message (int, float, FVector, etc):

int32 IntegerExample = 4; // you can use int8, uint8, int16, uint16, int32, uint32, int64, uint64 to log this way
float FloatExample = 10.4;
FVector VectorExample = FVector(100, 200, 300);
GEngine->AddOnScreenDebugMessage(-1, 12.f, FColor::White, FString::Printf(TEXT("Output: %d %f %s"), IntegerExample, FloatExample, *VectorExample.ToString()));

Much more detailed information is available on the UE4 Community Wiki page