Create Blueprint Library, print to log and using windows.h in a Unreal Engine C++ project

When you need to use some specific Windows API functions,

such as LoadLibrary for loading DLL, or CreateFileMapping for using shared memory,

you need to use #include <windows.h> in your project's C++ code.

To be sure all building successfully, please insert this with "WIN32_LEAN_AND_MEAN" define, and use it as early as possible (I use it as the second #include in CPP code):

#include "MyBlueprintFunctionLibrary.h"
#define WIN32_LEAN_AND_MEAN
#include <windows.h>

For advanced capabilites, such as using GEngine class, it's required to include "Engine.h". It's required to do before including <windows.h> :

#include "MyBlueprintFunctionLibrary.h"
#include "Engine.h"
#define WIN32_LEAN_AND_MEAN
#include <windows.h>

Here is example how to load DLL using Windows API in Blueprint Function Library C++ class.

Also, it demonstrates print to screen and to log in Unreal Engine C++ and convert FString to std::string.

.h-file
Here you can see how to declare functions in Blueprint Function Library.



#pragma once

#include "CoreMinimal.h"
#include "Kismet/BlueprintFunctionLibrary.h"
#include "MyBlueprintFunctionLibrary.generated.h"

UCLASS()
class OSCSEND_API UMyBlueprintFunctionLibrary : public UBlueprintFunctionLibrary
{
    GENERATED_BODY()


    UFUNCTION(BlueprintCallable, Category = "OSC",    meta = (DisplayName = "OSC Receive Start"))
        static void osc_receive_start(int port);
    //NOTE: for further usage also need stop too

    UFUNCTION(BlueprintCallable, Category = "OSC", meta = (DisplayName = "OSC Receive Message"))
        static FString osc_receive();

    UFUNCTION(BlueprintCallable, Category = "OSC", meta = (DisplayName = "OSC Send Message"))
        static void osc_send(FString host, int port, FString message);

};
 

.cpp-file






Here  is demonstrated how to print to screen and log, convert FString to std::string

#include "MyBlueprintFunctionLibrary.h"

#include "Engine.h"
#define WIN32_LEAN_AND_MEAN
#include <windows.h> 
#include <string>

//------------------------------------------------------------------
//Common functions
#define _PRINT(text) { if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 2, FColor::White,std::string(text).c_str()); }
#define _PRINT_FSTRING(text) { if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 2, FColor::White,text); }
#define _LOG(text) UE_LOG(LogTemp, Warning, TEXT(text));

std::string toString(FString v) {
    return TCHAR_TO_UTF8(*v);
}
//------------------------------------------------------------------

HMODULE hModule_ = 0;    //handle to DLL

typedef  void(_cdecl* send_command_DEF)  (const char *s, const char *host, int port);
typedef void (_cdecl* start_receiver_DEF) (int port);
typedef  const char *(_cdecl* receive_message_DEF)  ();

send_command_DEF            send_command = 0;
start_receiver_DEF            start_receiver = 0;
receive_message_DEF         receive_message = 0;


//------------------------------------------------------------------
void load_dll() {
    if (!hModule_) {
        FString file_name = FPaths::GameDir() + "Binaries/Win64/SimpleOSC.dll";
        if ((hModule_ = LoadLibrary(*file_name)) == NULL) {
            _PRINT_FSTRING("ERROR: Can't load OSC DLL: " + file_name);
        }
        else {
            _PRINT("OSC DLL is loaded");
        }

        send_command = (send_command_DEF)GetProcAddress(hModule_, "send_command");
        start_receiver = (start_receiver_DEF)GetProcAddress(hModule_, "start_receiver");
        receive_message = (receive_message_DEF)GetProcAddress(hModule_, "receive_message");
        if (!send_command) {
            _PRINT("OSC DLL ERROR: no send_command");
        }
        if (!start_receiver) {
            _PRINT("OSC DLL ERROR: no start_receiver");
        }
        if (!receive_message) {
            _PRINT("OSC DLL ERROR: no receive_message");
        }

    }
}


//------------------------------------------------------------------
void UMyBlueprintFunctionLibrary::osc_receive_start(int port) {
    load_dll();
    if (start_receiver) {
        start_receiver(port);
    }
}

//------------------------------------------------------------------
FString UMyBlueprintFunctionLibrary::osc_receive() {
    if (receive_message) {
        return FString(receive_message());
    }
    return FString("");
}

//------------------------------------------------------------------
void UMyBlueprintFunctionLibrary::osc_send(FString host, int port, FString message) {
    load_dll();
    if (send_command) {
        std::string s = toString(message);
        std::string shost = toString(host);
        send_command(s.c_str(), shost.c_str(), port);
    }

}

//------------------------------------------------------------------