Is there a way to change something that has already been written to the console?
For example, I'd like to change a line already written from this:
_ Foo
... to this:
+ Foo
Although ideally this would work on both Windows (powershell or command line) and Linux (shell), a Linux-only solution would be acceptable.
I'm unfamiliar with standard input and output, so forgive me if this is a basic question.
If your cursor is still on the same line you can do this:
write("_ Foo");
stdout.fllush;//To force the displaying of the text now.
writeln("\r+ Foo"); //Output will be replaced
But this will not work:
writeln("_ Foo"); //Equivalent to as `write("_ Foo\n");`
stdout.fllush;//To force the displaying of the text now
writeln("\r+ Foo"); //Output will not be replaced (it will be on new line).
You can also do this to erase characters individually:
write("_ Foo");
stdout.fllush;//To force the displaying of the text now
writeln("\b+ Foo"); //Output will be "_ Fo+ Foo"
I have not found a way to erase previous lines (and I think this is intentional).
Related
I've been trying to read from a file to console and then clear it to read another file.
So I found out you can remove characters from console by using '\b'. However when I try to remove previous content from console it only removes the last line and then stops.
Something like this:
std::cout<<"Something boring"<<'\n'<<"Something boring on new line";
while(1){
std::cout<<'\b';
std::cout<<' ';
std::cout<<'\b';
}
This will only remove "Something boring on new line", and as far as I can see the cursor is on the first position of line 2.
Why does it get stuck and can something be done about it?
Thanks.
I'm working on a c++ console project and i would like to show a percentage without making a new line each time (so that the window doesn't get clogged with thousands of lines).
Is there a way of removing the last line that was printed or something to say that the next time that i output a line it should replace the current line?
You can use a \r (carriage return) to return the cursor to the beginning of the line:
This works on windows and Linux.
From: Erase the current printed console line
You could alternatively use a series of backspaces.
string str="Hello!";
cout << str;
cout << string(str.length(),'\b');
cout << "Hello again!";
From: http://www.cplusplus.com/forum/unices/25744/
Maybe mark as duplicate? I am really not sure how.
A simple example that I tested on Linux would be:
std::cout << "Some text to display..." << "\t\r" << std::flush;
Here the \t adds a tabulation to handle slightly varying string lengths and \r sends the cursor back at the start of the line (as mentioned in other answers).
std::flush is required to guarantee that the line is displayed without jumping to the next line.
This is very platform-dependent and terminal-dependent. But, you may want to look at ncurses for a start: http://linux.die.net/man/3/ncurses
For Windows: How can I overwrite the same portion of the console in a Windows native C++ console app, without using a 3rd Party library?
For Linux: https://unix.stackexchange.com/questions/43075/how-to-change-the-contents-of-a-line-on-the-terminal-as-opposed-to-writing-a-new
Well, the question may sound a bit too vague but here's 2 things I need to do and I'd definitely need some input on this :
Output something (e.g. using cout) with color (note: My TERM environment variable is set to xterm-color if that makes any difference; also, is there any uniform way to output colored text that's compatible with both pure mac and *nix terminals in general, so that the code is portable)
Output something at the same position on the terminal screen. OK, this may sound confusing too. Let's take a terminal app which simply outputs a progress percentage. It normally won't start a new line for that. The new value is shown at the very same spot. How is this doable? (Being a once Borland Pascal guy from the good old DOS days, the only thing I could think of is something to do with accessing video memory directly... or not?)
So... any ideas?
You probably want to use ncurses library. And ANSI escape codes can also be used for coloring.
1)
You can try Color cout , but that is not protable. I tried (ANSI escape codes) something like
cout << "\033[1;31mbold red text\033[0m\n";
cout << "\33[0;31m" << "Enter Your String here" << "\33[0m" << std::endl ;
You can also look at
How do I output coloured text to a Linux terminal?
2)
Are you looking for something like watch or top like app which are showing output at the same spot.
Question should say it all.
Let's say there's a local file "mydefaultvalues.txt", separated from the main project. In the main project I want to have something like this:
char * defaultvalues = " ... "; // here should be the contents of mydefaultvalues.txt
And let the compiler swap " ... " with the actual contents of mydefaultvalues.txt. Can this be done? Is there like a compiler directive or something?
Not exactly, but you could do something like this:
defaults.h:
#define DEFAULT_VALUES "something something something"
code.c:
#include "defaults.h"
char *defaultvalues = DEFAULT_VALUES;
Where defaults.h could be generated, or otherwise created however you were planning to do it. The pre-processor can only do so much. Making your files in a form that it will understand will make things much easier.
The trick I did, on Linux, was to have in the Makefile this line:
defaultvalues.h: defaultvalues.txt
xxd -i defaultvalues.txt > defaultvalues.h
Then you could include:
#include "defaultvalues.h"
There is defined both unsigned char defaultvalues_txt[]; with the contents of the file, and unsigned int defaultvalues_txt_len; with the size of the file.
Note that defaultvalues_txt is not null-terminated, thus, not considered a C string. But since you also have the size, this should not be a problem.
EDIT:
A small variation would allow me to have a null-terminated string:
echo "char defaultvalues[] = { " `xxd -i < defaultvalues.txt` ", 0x00 };" > defaultvalues.h
Obviously will not work very well if the null character is present inside the file defaultvalues.txt, but that won't happen if it is plain text.
One way to achieve compile-time trickery like this is to write a simple script in some interpreted programming language(e.g. Python, Ruby or Perl will do great) which does a simple search and replace. Then just run the script before compiling.
Define your own #pramga XYZ directive which the script looks for and replaces it with the code that declares the variable with file contents in a string.
char * defaultvalues = ...
where ... contains the text string read from the given text file. Be sure to compensate for line length, new lines, string formatting characters and other special characters.
Edit: lvella beat me to it with far superior approach - embrace the tools your environment supplies you. In this case a tool which does string search and replace and feed a file to it.
Late answer I know but I don't think any of the current answers address what the OP is trying to accomplish although zxcdw came really close.
All any 7 year old has to do is load your program into a hex editor and hit CTRL-S. If the text is in your executable code (or vicinity) or application resource they can find it and edit it.
If you want to prevent the general public from changing a resource or static data just encrypt it, stuff it in a resource then decrypt it at runtime. Try DES for something small to start with.
printf("Error %d\n", 1);
printf("\nStatus: %d%%", 50);
prints
Error 1
Status: 50%
In this set up, is there any chance to insert Error 2\n between Error 1\n and \nStatus: 50%. I understand that \r and \b can be used to change printed text in the same line (e.g., if there is a single \n between Error 1 and Status: 50%), but can I change text in a previous line?
Thanks!
What #Ryan said.
Explanation why: stdout is some abstract stream that doesn't have to be the terminal. It may be a file, a pipe, a socket, a printer, a text to speech device or whatever. In many cases there is no sense to what you asked to do. Hence you need some library that works with the terminal specifically.
Sorry, you cannot.
But you may issue system calls to clear the whole screen instead, like system("clear") (OS-dependent).
Or use ncurses just as Kos mentioned in the comment.
You could use ANSI Escapesequences to move your "cursor" one line up:
void cursorOnLineUp(void) { printf("\033[1A"); }
Or set it to a specific position:
void setCursor(int column, int row) { printf("\033[%d;%dH", row, column) }
Haven't tried it for C++, but succesfully used it for a simple game in ANSI-C!