Something

public UpdatePlayerMapPos(playerid)
{
  new Float:X,Float:Y,Float:Z;
  new map_pos[256];
  new File:fhandle;
  fhandle = fopen("map_pos.txt",io_write);
  format(map_pos,sizeof(map_pos),"");
  fclose(fhandle);
  for(new i = 0; i < MAX_PLAYERS; i++){
    GetPlayerPos(i,X,Y,Z);
    GetPlayerName(i, playername, sizeof(playername));
    fhandle = fopen("map_pos.txt",io_append);
    format(map_pos,sizeof(map_pos),"%d %s %0.2f %0.2f\n",i,playername,X,Y);
    fwrite(fhandle,map_pos);
    fclose(fhandle);
    }
}