Terminal Emulator scrolling in SDL

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C++

C

Linux

C++11

Hi guys :)
I've been reading about libSDL (Simple Direct Media Layer), which is a portable library designed for creating games, emulators etc. i.e. applications that require graphical effects rather than using the old legacy console.
As a simple exercise I've been trying to emulate a console (not to the very extent), I've implemented the basics (putchar, puts, printf) and now I'm trying to implement a scroll() function which'll scroll i.e. copy from the 2nd row to the last row to the 1st row and the second last row. Here's how I do it:

// End of screen?
if (screen_y >= GL_MAX_Y)
	{
		// Yes. Scroll
		// This basically involves copying a part of the screen on the screen itself
		SDL_Rect temp;
		temp.x = 0; // X co-ordinate 
		temp.y = FONT_HEIGHT; // Y-cord First Row (In scrolling, the 0th row is replaced by the 1st row)
		temp.h = GL_MAX_Y; // ...And copy till the last line
		temp.w = GL_MAX_X; // Width should be the screen
		// COPY!
		SDL_BlitSurface(screen, &temp, screen, NULL);
		// Set X to 0
		screen_x = 0;
		// Set Y to last row 
		screen_y = GL_MAX_Y - FONT_HEIGHT;
	}

This scrolls perfectly, but the last line is filled with junk from the first line.
Is there any way I can clear the last line of the screen?