Hello everyone,
thanks in advance for the answers.
Use Visual Express 2013 on W7.
Libraries: SDL, OpenGL.

So this is the problem, if I load a texture in OpenGL I use SDL_GL_BindTexture which in turn needs a SDL_texture.
To load SDL_texture I have to use this function SDL_CreateTextureFromSurface.
SDL_CreateTextureFromSurface needs a render that I do not use because I do have to render OpenGL instead of SDL!

myTexture.cpp
Code :
bool myTexture::loadTextureFromFile(std::string path)
{
	bool success = true;
	SDL_Texture* newTexture = NULL;
 
	//Load image at specified path
	SDL_Surface* loadedSurface = IMG_Load(path.c_str());
	if (loadedSurface == NULL)
	{
		printf("Unable to load image %s! SDL_image Error: %s\n", path.c_str(), IMG_GetError());
	}
	else
	{
		//Create texture from surface pixels
		//newTexture = SDL_CreateTextureFromSurface(gRenderer, loadedSurface);//<######################problem!
		if (newTexture == NULL)
		{
			printf("Unable to create texture from %s! SDL Error: %s\n", path.c_str(), SDL_GetError());
		}
 
		//Get rid of old loaded surface
		SDL_FreeSurface(loadedSurface);
	}
 
	mTexture = newTexture;
	return success;
}

myWindow.cpp
Code :
bool myWindow::init()
{
	printf("\nInitWindowSDL________________ \n");
	//Create window
	mWindow = SDL_CreateWindow("window", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_OPENGL | SDL_WINDOW_HIDDEN | SDL_WINDOW_RESIZABLE);
	if (mWindow != NULL)
	{
		mMouseFocus = true;
		mKeyboardFocus = true;
		mWidth = SCREEN_WIDTH;
		mHeight = SCREEN_HEIGHT;
 
		//Create renderer for window
		mContext = SDL_GL_CreateContext(mWindow);
		if (mContext == NULL)
		{
			printf("Errore SDL_GL_CreateContext():\n%s\n", SDL_GetError());
			SDL_DestroyWindow(mWindow);
			mWindow = NULL;
		}
		else
		{
			printf("Context creato.\n");
 
			//Grab window identifier
			mWindowID = SDL_GetWindowID(mWindow);
			printf("Finestra creata: %d.\n", mWindowID);
			//Flag as opened
			mShown = false;
		}
	}
	else
	{
		printf("Errore SDL_CreateWindow():\n%s\n", SDL_GetError());
	}
	printf("_____________________________ \n");
	return mWindow != NULL && mContext != NULL;
}
The question is I have to create a dummy invisible window in the class myTexture to have the render I need or there are other features that I can use in place of SDL_CreateTextureFromSurface?

PS: Sorry for my english.