How to set carriage return location or equivalent?

I am looking for a way to set where the carriage return, returns to or an equivalent way to do so.

For example I have a line like this:

^ denotes cursor location

myshell>cat file.txt
                    ^

After carriage return it should look like this.

myshell>cat file.txt
        ^

Solution

You're probably after what's collectively called ANSI escape sequences. Its hard to search for if you really have no idea what you're after.

This tiny example saves/restores cursor position:

#include <stdio.h>

int main(int argc, char**argv)
{
  char cmd_buf[100];
  cmd_buf[0]=0;
  while(strncmp(cmd_buf, "quit", 4))
  {
    printf("mypromt>\033[s <-Cursor should go there\033[u");
    fflush(stdout);
    fgets(cmd_buf, sizeof(cmd_buf), stdin);
    printf("\nYou entered: %s\n", cmd_buf);
  }
}

Note that in terminator, gnome-terminal and xterm on Ubuntu, this "magically" supports CTRL+U as-is, but not CTRL+A or CTRL+E.

There are many, many more sequences available. The wikipedia page is probably the simplest reference to get you started.

Update: Also, unless you're doing this as a learning exercise (which I get the impression Benjamin is), to build an interactive shell, you should probably use one of the two well established libraries for shell-style line editing, namely:

readline (GPLv3, but far more popular)
editline (BSD licensed, closest "second place")

They are the libraries that provide the emacs-style (typical default) and vi-style keybindings and history features we all know and love from bash, python, lua, perl, node, etc, etc.