To do this in C++ / Unreal, you need to do the following either in (or called by) EventTick or on a timer:

// Set up parameters for getting the player viewport
    FVector PlayerViewPointLocation;
    FRotator PlayerViewPointRotation;

// Get player viewport and set these parameters
    GetWorld()->GetFirstPlayerController()->GetPlayerViewPoint(
    OUT PlayerViewPointLocation, 
    OUT PlayerViewPointRotation
    );

// Parameter for how far out the the line trace reaches
    float Reach = 100.f;
    FVector LineTraceEnd = PlayerViewPointLocation + PlayerViewPointRotation.Vector() * Reach;

// Set parameters to use line tracing
    FHitResult Hit; 
    FCollisionQueryParams TraceParams(FName(TEXT("")), false, GetOwner());  // false to ignore complex collisions and GetOwner() to ignore self

// Raycast out to this distance
    GetWorld()->LineTraceSingleByObjectType(
        OUT Hit,
        PlayerViewPointLocation,
        LineTraceEnd,
        FCollisionObjectQueryParams(ECollisionChannel::ECC_PhysicsBody),
        TraceParams
    );

// See what if anything has been hit and return what
    AActor* ActorHit = Hit.GetActor();

    if (ActorHit) {
        UE_LOG(LogTemp, Error, TEXT("Line trace has hit: %s"), *(ActorHit->GetName()))
    }

This will return the first actor that has been hit. If you want to find a specific actor, you can say:

if (ActorHit == Cast<AYourCustomActorClass>YourCustomClass)

Which will only return true if the first item hit is the specific class you're looking for.

To do this in C++ / Unreal, you need to do the following either in (or called by) EventTick or on a timer:

// Set up parameters for getting the player viewport
    FVector PlayerViewPointLocation;
    FRotator PlayerViewPointRotation;

// Get player viewport and set these parameters
    GetWorld()->GetFirstPlayerController()->GetPlayerViewPoint(
    OUT PlayerViewPointLocation, 
    OUT PlayerViewPointRotation
    );

// Parameter for how far out the the line trace reaches
    float Reach = 100.f;
    FVector LineTraceEnd = PlayerViewPointLocation + PlayerViewPointRotation.Vector() * Reach;

// Set parameters to use line tracing
    FHitResult Hit; 
    FCollisionQueryParams TraceParams(FName(TEXT("")), false, GetOwner());  // false to ignore complex collisions and GetOwner() to ignore self

// Raycast out to this distance
    GetWorld()->LineTraceSingleByObjectType(
        OUT Hit,
        PlayerViewPointLocation,
        LineTraceEnd,
        FCollisionObjectQueryParams(ECollisionChannel::ECC_PhysicsBody),
        TraceParams
    );

// See what if anything has been hit and return what
    AActor* ActorHit = Hit.GetActor();

    if (ActorHit) {
        UE_LOG(LogTemp, Error, TEXT("Line trace has hit: %s"), *(ActorHit->GetName()))
    }

This will return the first actor that has been hit. If you want to find a specific actor, you can say:

if (ActorHit == Cast<AYourCustomActorClass>(YourCustomClass))

Which will only return true if the first item hit is the specific class you're looking for.