Hi, how can i prevent erase of screen data while scrolling. When i use the ANSI cursor movement commands(\027[PnS , \027[PnT etc) say for scroll down the top lines get erased. i.e. if i scroll up after scroll down, i am unable to view top lines again.

Where are you scrolling? In a virtual terminal? In a console? In another program?

in a console

You can always use "less"

Actually it is a c program and uses ansi command set to scroll (\027[PnS & \027[PnT ).

OK - there's your answer. It's the program's fault

Think about it: who's supposed to "remember" the text that scrolls off the screen?

If it's an X terminal with scrollbars, it's the "xterm" executable that buffers the unseen text. Similarly, "less", "vi", "emacs" et al each have their own strategies for saving, displaying and retrieving text.

It sounds like all your program does is "read" and "scroll". You can probably scroll forward just because the text that comes next is still waiting to be read. But you can't scroll backward - because the program never saved (and cannot retrieve) what it already read.

I'd forget the ANSI character sequences, if you have any choice in the matter.

Two better alternatives:
1. Use your program in conjunction with an external scrolling tool (like "less")
2. Use a more robust screen control library (like "ncurses").

thanks, it means we need to save and display( by own logic) while scroll back, console is not doing it for us....