I am too confused with console screen. I am not able to figure out how to move cursor to random position. This is my code:
#include<iostream>
#include<conio.h>
main()
{
cout<<"Hello World";
return 0;
}
I want to move cursor to random position, not at the beginning after pressing Enter.
There is no standard way to affect the terminal cursor in C++. So, the first step in implementing this is to figure out what system you are targetting, and what API it offers.
Related
I'm currently designing a CLI interface for linux, and for various reasons I am not able to use ncurses. I am using exclusively C++ and the Qt framework.
Therefore, in order to have a user-friendly interface, I have to run this getch loop in a separate thread:
https://stackoverflow.com/a/912796/3605689
Which basically means I have to implement all basic functionalities (such as backspace) by myself. I have already implemented command completion and command history(like when you press tab or uparrow/downarrow in linux), but I can't figure out how to implement leftarrow/rightarrow (aka seeking through the typeahead).
Normally, I implement it like this: upon every gech which is not equal to -1, I check whether the user has pressed a special key (one that modifies the typeahead somehow). I then clear the stdout using the following function:
void inputobject::clear_line(int nletters)
{
QTextStream(stdout) << "\033[2K";
for(int i = 0; i < nletters;i++){
QTextStream(stdout) << "\b";
}
rewind(stdout);
}
And replace it with something else, effectively simulating the typeahead. For example, in the case of backspace, I would save the command call clear_line, and print the command out again, just with one less letter, behaving exactly as a normal console application would.
My real problem is with the cursor, in the case of left/rightarrow, I need to move the cursor visual in order to be able to indicate where in the text is the user seeking:
Because of the nature of how I rewrite the given stdout line to simulate the typeahead, it does not really matter where the cursor REALLY is, as long as it stays on the same line - it is just the visual that matters. How can I achieve moving the cursor visual on linux?
The answer was provided in the comment by Evilruff:
Cursor Movement
ANSI escape sequences allow you to move the cursor around the screen at will. This is more useful for full screen user interfaces generated by shell scripts, but can also be used in prompts. The movement escape sequences are as follows:
Position the Cursor:
\033[;H
Or
\033[L;Cf
puts the cursor at line L and column C.
Move the cursor up N lines:
\033[NA
Move the cursor down N lines:
\033[NB
Move the cursor forward N columns:
\033[NC
Move the cursor backward N columns:
\033[ND
Clear the screen, move to (0,0):
\033[2J
Erase to end of line:
\033[K
Save cursor position:
\033[s
Restore cursor position:
\033[u
Not using ncurses and co is a serious limitation.
It is hell to make correct input/output on shell for displaying anything.
The only others real solutions (I can't think as a solution to reimplement a ncurse-like library) I think of are:
making call to dialog (for some example www.linuxjournal.com/article/2807 and for the doc: http://linux.die.net/man/1/dialog)
using the framebuffer mecanism with Qt4 (here)
I am using ncurses to develop an application in C++ but both the newwin() and mvwin() functions are not working as expected. Whenever I give either of these function argument values in an attempt to make a new window that is of different size then the initial terminal window, nothing appears to happen. For example, the following code should create a new window with a height of 50, a width of 10, at location (10,10). None of this appears to be happening:
#include <ncurses.h>
#include <iostream>
using namespace std;
int main(){
initscr();
WINDOW * win = newwin(50,10,10,10);
wrefresh(win);
getch();
endwin();
return 0;
}
From the documentation I have read, it appears that a window will be created with default sizing and location if any of the arguments passed to it are invalid values, but to my knowledge all of these are valid values. Does newwin() not work like I think it does? Thank you in advance
The question asks about mvwin, but that does not create windows, nor is there an example in the question of a problematic call.
For newwin, zero parameters are handled specially, not "invalid values". The question shows an apparently valid call (and in a quick check, it runs as expected).
However, OP is likely confused that there is no output. That is because the program creates a window, which is empty and then reads from the standard screen.
This altered program produces output by drawing a box on the new window and then reading from that window (preventing the wrefresh associated with getch from painting over the new window):
#include <ncurses.h>
#include <iostream>
using namespace std;
int main(){
initscr();
WINDOW * win = newwin(50,10,10,10);
box(win,0,0);
wrefresh(win);
wgetch(win);
endwin();
return 0;
}
It sounds like there's some misunderstanding here of what ncurses does.
You mention an "attempt to make a new window that is of different size then the initial terminal window" -- if you mean a terminal emulator running in a windowing system like X/OSX/Windows, that is not what ncurses does. A "window" in ncurses is a rectangle within an existing terminal that can be updated/refreshed independently.
This might be why the comments on the other answer seem to be talking past each other.
Why does my C++ output screen disappear immediately? I'm a beginner in cpp. Can anyone help me to find the problem please?
You should either launch your application inside of a terminal, or add a line of code that waits for the input in order for the window to not close. E.g. add in the end of the function main a line:
std::cin.get();
And also add at beginning of the file the include that holds that function.
#include <iostream>
This is hard to answer since there can be many things that can cause your output box to close immediately. First try having a cout statement and then a cin statement. Something like:
cout<<"Hello"<<endl;
cin>>input>>endl;
Also make sure to have the necessary include statement at the top and whatever you want to return at the bottom.
#include<iostream>
return 0;
As you have said that you are beginner in C++, you should keep in mind ,three major things while coding in C++. You've mentioned that your screen disappears , then following things you should try.
1). in C++ conventionally main returns value of type int.And the format of your program should be like...
int main()
{
-------
//body of your program
-------
return 0;
}
If the function returns 0, that means it ran successfully.
2). You have to inlcude #include<iostream> on the top of your program.
3).check whether the IDE you are using is compatibale to your operating system or not.
Hope this will help you.
I use the following lines to output my simulation's progress info in my c++ program,
double N=0;
double percent=0;
double total = 1000000;
for (int i; i<total; ++i)
{
percent = 100*i/total;
printf("\r[%6.4f%%]",percent);
}
It works fine!
But the problem is I see the terminal cursor keeps blinking cyclically through the numbers, this is very annoying, anyone knows how to get rid of this?
I've seen some programs like wget or ubuntu apt, they use progress bar or percentages too, but they seems no blinking cursor issue, I am wondering how did they do that?
Thanks!
You can hide and show the cursor using the DECTCEM (DEC text cursor enable mode) mode in DECSM and DECRM:
fputs("\e[?25l", stdout); /* hide the cursor */
fputs("\e[?25h", stdout); /* show the cursor */
Just a guess: try to use a proper number of '\b' (backspace) characters instead of '\r'.
== EDIT ==
I'm not a Linux shell wizard, but this may work:
system("setterm -cursor off");
// ...display percentages...
system("setterm -cursor on");
Don't forget to #include <cstdlib> or <iostream>.
One way to avoid a blinking cursor is (as suggested) to hide the cursor temporarily.
However, that is only part of the solution. Your program should also take this into account:
after hiding the cursor and modifying the screen, before showing the cursor again move it back to the original location.
hiding/showing the cursor only keeps the cursor from noticeably blinking when your updates take only a small amount of time. If you happened to mix this with some time-consuming process, your cursor will blink.
The suggested solution using setterm is not portable; it is specific to the Linux console. And running an executable using system is not really necessary. But even running
system("tput civis");
...
system("tput cnorm");
is an improvement over using setterm.
Checking the source-code for wget doesn't find any cursor-hiding escape sequences. What you're seeing with its progress bar is that it leaves the cursor in roughly the same place whenever it does something time-consuming. The output to the terminal takes so little time that you do not notice the momentary rewrite of the line (by printing a carriage return, then writing most of the line over again). If it were slower, then hiding the cursor would help — up to a point.
By the way — this cursor-hiding technique is used in the terminal drivers for some editors (vim and vile).
Those apps are probably using ncurses. See mvaddstr
The reason the cursor jumps around is because stdout is buffered, so you don't know actually how many characters are being printed at some point in time. The reason wget does not have a jumping cursor is that they are actually printing to stderr instead, which is unbuffered. Try the following:
fprintf(stderr, "\r[%6.4f%%]", percent);
This also has the advantage of not cluttering the file if you are saving the rest of the output somewhere using a pipe like:
$ ./executable > log.data
Press insert key...if that doesn't work then press the fn key in your keyboard.
This will definitely work
Hope this helps
I am trying to make the copies of the builtin functions and adding a x to their name so i can understand each functions working.While writing a function for clrscr() i am confused about how it works.Does it use 2 nested loops and print (" ") i.e space all over the screen or it prints("\n") over the screen?Or what?
I tried this:
#include<stdio.h>
#include<conio.h>
void main(void)
{
printf("press any key to make clrscr() work");
getch();
for(int i=0;i<50;i++)
{
printf("\n");
}
// to make the screen come to 1,1
gotoxy(1,1);
getch();
}
clrscr() implementation may depend on the environment your console application runs. Usually it sends the ClearScreen control character (0x0C) to the console driver, that actually clears the screen.
The driver knows about character space to clear as well as all attributes (blink, underline,...) to reset.
If you dont want the driver to handle 0x0C, you can mimic this with 50 times calling printf("\n"). but calling 50x80 calling poutchar(' ') is not similar to calling clrsrc(), since the cursor will be advanced by one what may put it in the next line after scrolling the screen content.
Further you should regard, that the behaviour of the screen depends on the implementation. When the cursor position is in the right column and you output one character the cursor position may stay at the right edge or it may cause a new line. Whe you cursor position is in the lower right corner the next character may cause a new line including scrolling the screen content by one line.
The best way would be to imaging what clrscr() would do and let it make it's job.