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I have a GUI application whose main part is a QPlainTextEdit. It is used to display a log of the application, and as such the associated text grows line by line ad infinitum.
As the application is intended to run very long, I need to limit the memory that will be allocated for this log. Therefore I want to have some maxNumLines or maxNumCharacters parameter that will make sure the history will be truncated when reached, i.e. the head lines will be removed as new lines are appended (a.k.a. log rotation).
To achieve this I found the functions
// get the associated text
QString toPlainText () const
// set the associated text
void setPlainText ( const QString & text )
Therefore something like this untested code would probably do the trick:
QString &tmp = pte.toPlainText();
while (tmp.size() > maxNumCharacters) {
// remove lines from the head of the string until the desired size is reached
// removes nothing if "\n" could not be found
tmp.remove(0, tmp.indexOf("\n")+1);
}
pte.setPlainText( tmp );
Is this the way to go to remove the first line(s) from the QPlainTextEdit? Are there probably other Qt Text GUI elements that would better fit to this task (set a maximum number of lines and truncate at the head of the list), e.g. somehow display a QStringList in which I could store the lines (s.t. I could easily erase(0))?
Or does the QPlainTextEdit eventually implement such upper bound for the size of the associated QString after all?
Apparantly the property maximumBlockCount is exactly what I need:
If you want to limit the total number of paragraphs in a QPlainTextEdit, as it is for example useful in a log viewer, then you can use the maximumBlockCount property. The combination of setMaximumBlockCount() and appendPlainText() turns QPlainTextEdit into an efficient viewer for log text.
For reference:
http://doc.qt.io/qt-5/qplaintextedit.html#maximumBlockCount-prop
I had exactly the same problem a months back, and I ended up using a QListView. Although using the model/view/delegate architecture is a bit more fiddly, it scales much better in the long run. For example once the basic architecture is in place, adding a filter that displays only error or warning entries becomes trivial, or creating a delegate so that the background of error entries are painted red is also straightforward.
I am new to programming with no formal programming training, so please excuse this newbie question. I can't seem to find a definitive answer on it, and need to be sure.
Here's the scenario: sometimes I need to try different lines of code to see if they work, but still want to keep the original lines in there in case the new lines don't work (or for future reference). I thought by putting // in front of the line I want to "comment out" would mean the line of code would be ignored when compiling the program, but my app crashed and pointed to a line I thought was commented out. I am using Xcode 4.
Is there another symbol I should be using to comment out lines or blocks of code? For example, will /* at the beginning and */ at the end accomplish this?
For "commenting out" big blocks of code, I do conditionals like:
#if I_AM_TESTING_SO_DONT_COMPILE_THIS
...
...
...
...
#endif // I_AM_TESTING_SO_DONT_COMPILE_THIS
And yes, the traditional C-style /* and */ also work to "comment out" blocks of code.
The reason your compile crashed with // is because while a single line gets commented out, you might have had some extra code on a second line.
Such as:
//NSString * someContentFromSomewhere = [[NSString alloc] initWithContentsOfURL:
[NSURL URLWithString: #"http://www.stackoverflow.com"]];
The first line is commented out. The second line is a syntax error.
Also, make sure you do a clean build. It's possible that sometimes old object files are used and even though you commented out a line in the IDE, it may not have build with that updated file.
I am making a C application in Unix that uses raw tty input.
I am calling write() to characters on the display, but I want to manipulate the cursor:
ssize_t
write(int d, const void *buf, size_t nbytes);
I've noticed that if buf has the value 8 (I mean char tmp = 8, then passing &tmp), it will move the cursor/pointer backward on the screen.
I was wondering where I could find all the codes, for example, I wish to move the cursor forward but I cannot seem to find it via Google.
Is there a page that lists all the code for the write() function please?
Thank you very much,
Jary
8 is just the ascii code for backspace. You can type man ascii and look at all the values (the man page on my Ubuntu box has friendlier names for the values). If you want to do more complicated things you may want to look at a library like ncurses.
You have just discovered that character code 8 is backspace (control-H).
You would probably be best off using the curses library to manage the screen. However, you can find out what control sequences curses knows about by using infocmp to decompile the terminfo entry for your terminal. The format isn't particularly easy to understand, but it is relatively comprehensive. The alternative is to find a manual for the terminal, which tends to be rather hard.
For instance, I'm using a color Xterm window; infocmp says:
# Reconstructed via infocmp from file: /usr/share/terminfo/78/xterm-color
xterm-color|nxterm|generic color xterm,
am, km, mir, msgr, xenl,
colors#8, cols#80, it#8, lines#24, ncv#, pairs#64,
acsc=``aaffggiijjkkllmmnnooppqqrrssttuuvvwwxxyyzz{{||}}~~,
bel=^G, bold=\E[1m, clear=\E[H\E[2J, cr=^M,
csr=\E[%i%p1%d;%p2%dr, cub=\E[%p1%dD, cub1=^H,
cud=\E[%p1%dB, cud1=^J, cuf=\E[%p1%dC, cuf1=\E[C,
cup=\E[%i%p1%d;%p2%dH, cuu=\E[%p1%dA, cuu1=\E[A,
dch=\E[%p1%dP, dch1=\E[P, dl=\E[%p1%dM, dl1=\E[M, ed=\E[J,
el=\E[K, enacs=\E)0, home=\E[H, ht=^I, hts=\EH, il=\E[%p1%dL,
il1=\E[L, ind=^J,
is2=\E[m\E[?7h\E[4l\E>\E7\E[r\E[?1;3;4;6l\E8, kbs=^H,
kcub1=\EOD, kcud1=\EOB, kcuf1=\EOC, kcuu1=\EOA,
kdch1=\E[3~, kf1=\E[11~, kf10=\E[21~, kf11=\E[23~,
kf12=\E[24~, kf13=\E[25~, kf14=\E[26~, kf15=\E[28~,
kf16=\E[29~, kf17=\E[31~, kf18=\E[32~, kf19=\E[33~,
kf2=\E[12~, kf20=\E[34~, kf3=\E[13~, kf4=\E[14~,
kf5=\E[15~, kf6=\E[17~, kf7=\E[18~, kf8=\E[19~, kf9=\E[20~,
kfnd=\E[1~, kich1=\E[2~, kmous=\E[M, knp=\E[6~, kpp=\E[5~,
kslt=\E[4~, meml=\El, memu=\Em, op=\E[m, rc=\E8, rev=\E[7m,
ri=\EM, rmacs=^O, rmcup=\E[2J\E[?47l\E8, rmir=\E[4l,
rmkx=\E[?1l\E>, rmso=\E[m, rmul=\E[m,
rs2=\E[m\E[?7h\E[4l\E>\E7\E[r\E[?1;3;4;6l\E8, sc=\E7,
setab=\E[4%p1%dm, setaf=\E[3%p1%dm, sgr0=\E[m, smacs=^N,
smcup=\E7\E[?47h, smir=\E[4h, smkx=\E[?1h\E=, smso=\E[7m,
smul=\E[4m, tbc=\E[3g, u6=\E[%i%d;%dR, u7=\E[6n,
u8=\E[?1;2c, u9=\E[c,
That contains information about box drawing characters, code sequences generated by function keys, various cursor movement sequences, and so on.
You can find out more about X/Open Curses (v4.2) in HTML. However, that is officially obsolete, superseded by X/Open Curses v7, which you can download for free in PDF.
If you're using write just so you have low-level cursor control, I think you are using the wrong tool for the job. There are command codes for many types of terminal. VT100 codes, for example, are sequences of the form "\x1b[...", but rather than sending raw codes, you'd be much better off using a library like ncurses.
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Closed 11 years ago.
There are a plethora of questions where people talk about common tricks, notably "Vim+ctags tips and tricks".
However, I don't refer to commonly used shortcuts that someone new to Vim would find cool. I am talking about a seasoned Unix user (be they a developer, administrator, both, etc.), who thinks they know something 99% of us never heard or dreamed about. Something that not only makes their work easier, but also is COOL and hackish. After all, Vim resides in the most dark-corner-rich OS in the world, thus it should have intricacies that only a few privileged know about and want to share with us.
Might not be one that 99% of Vim users don't know about, but it's something I use daily and that any Linux+Vim poweruser must know.
Basic command, yet extremely useful.
:w !sudo tee %
I often forget to sudo before editing a file I don't have write permissions on. When I come to save that file and get a permission error, I just issue that vim command in order to save the file without the need to save it to a temp file and then copy it back again.
You obviously have to be on a system with sudo installed and have sudo rights.
Something I just discovered recently that I thought was very cool:
:earlier 15m
Reverts the document back to how it was 15 minutes ago. Can take various arguments for the amount of time you want to roll back, and is dependent on undolevels. Can be reversed with the opposite command :later
:! [command] executes an external command while you're in Vim.
But add a dot after the colon, :.! [command], and it'll dump the output of the command into your current window. That's : . !
For example:
:.! ls
I use this a lot for things like adding the current date into a document I'm typing:
:.! date
Not exactly obscure, but there are several "delete in" commands which are extremely useful, like..
diw to delete the current word
di( to delete within the current parens
di" to delete the text between the quotes
Others can be found on :help text-objects
de Delete everything till the end of the word by pressing . at your heart's desire.
ci(xyz[Esc] -- This is a weird one. Here, the 'i' does not mean insert mode. Instead it means inside the parenthesis. So this sequence cuts the text inside parenthesis you're standing in and replaces it with "xyz". It also works inside square and figure brackets -- just do ci[ or ci{ correspondingly. Naturally, you can do di (if you just want to delete all text without typing anything. You can also do a instead of i if you want to delete the parentheses as well and not just text inside them.
ci" - cuts the text in current quotes
ciw - cuts the current word. This works just like the previous one except that ( is replaced with w.
C - cut the rest of the line and switch to insert mode.
ZZ -- save and close current file (WAY faster than Ctrl-F4 to close the current tab!)
ddp - move current line one row down
xp -- move current character one position to the right
U - uppercase, so viwU upercases the word
~ - switches case, so viw~ will reverse casing of entire word
Ctrl+u / Ctrl+d scroll the page half-a-screen up or down. This seems to be more useful than the usual full-screen paging as it makes it easier to see how the two screens relate. For those who still want to scroll entire screen at a time there's Ctrl+f for Forward and Ctrl+b for Backward. Ctrl+Y and Ctrl+E scroll down or up one line at a time.
Crazy but very useful command is zz -- it scrolls the screen to make this line appear in the middle. This is excellent for putting the piece of code you're working on in the center of your attention. Sibling commands -- zt and zb -- make this line the top or the bottom one on the sreen which is not quite as useful.
% finds and jumps to the matching parenthesis.
de -- delete from cursor to the end of the word (you can also do dE to delete until the next space)
bde -- delete the current word, from left to right delimiter
df[space] -- delete up until and including the next space
dt. -- delete until next dot
dd -- delete this entire line
ye (or yE) -- yanks text from here to the end of the word
ce - cuts through the end of the word
bye -- copies current word (makes me wonder what "hi" does!)
yy -- copies the current line
cc -- cuts the current line, you can also do S instead. There's also lower cap s which cuts current character and switches to insert mode.
viwy or viwc. Yank or change current word. Hit w multiple times to keep selecting each subsequent word, use b to move backwards
vi{ - select all text in figure brackets. va{ - select all text including {}s
vi(p - highlight everything inside the ()s and replace with the pasted text
b and e move the cursor word-by-word, similarly to how Ctrl+Arrows normally do. The definition of word is a little different though, as several consecutive delmiters are treated as one word. If you start at the middle of a word, pressing b will always get you to the beginning of the current word, and each consecutive b will jump to the beginning of the next word. Similarly, and easy to remember, e gets the cursor to the end of the current, and each subsequent, word.
similar to b/e, capital B and E move the cursor word-by-word using only whitespaces as delimiters.
capital D (take a deep breath) Deletes the rest of the line to the right of the cursor, same as Shift+End/Del in normal editors (notice 2 keypresses -- Shift+D -- instead of 3)
One that I rarely find in most Vim tutorials, but it's INCREDIBLY useful (at least to me), is the
g; and g,
to move (forward, backward) through the changelist.
Let me show how I use it. Sometimes I need to copy and paste a piece of code or string, say a hex color code in a CSS file, so I search, jump (not caring where the match is), copy it and then jump back (g;) to where I was editing the code to finally paste it. No need to create marks. Simpler.
Just my 2cents.
:%!xxd
Make vim into a hex editor.
:%!xxd -r
Revert.
Warning: If you don't edit with binary (-b), you might damage the file. – Josh Lee in the comments.
gv
Reselects last visual selection.
Sometimes a setting in your .vimrc will get overridden by a plugin or autocommand. To debug this a useful trick is to use the :verbose command in conjunction with :set. For example, to figure out where cindent got set/unset:
:verbose set cindent?
This will output something like:
cindent
Last set from /usr/share/vim/vim71/indent/c.vim
This also works with maps and highlights. (Thanks joeytwiddle for pointing this out.) For example:
:verbose nmap U
n U <C-R>
Last set from ~/.vimrc
:verbose highlight Normal
Normal xxx guifg=#dddddd guibg=#111111 font=Inconsolata Medium 14
Last set from ~/src/vim-holodark/colors/holodark.vim
:%TOhtml
Creates an html rendering of the current file.
Not sure if this counts as dark-corner-ish at all, but I've only just learnt it...
:g/match/y A
will yank (copy) all lines containing "match" into the "a/#a register. (The capitalization as A makes vim append yankings instead of replacing the previous register contents.) I used it a lot recently when making Internet Explorer stylesheets.
Want to look at your :command history?
q:
Then browse, edit and finally to execute the command.
Ever make similar changes to two files and switch back and forth between them? (Say, source and header files?)
:set hidden
:map <TAB> :e#<CR>
Then tab back and forth between those files.
Vim will open a URL, for example
vim http://stackoverflow.com/
Nice when you need to pull up the source of a page for reference.
Macros can call other macros, and can also call itself.
eg:
qq0dwj#qq#q
...will delete the first word from every line until the end of the file.
This is quite a simple example but it demonstrates a very powerful feature of vim
Assuming you have Perl and/or Ruby support compiled in, :rubydo and :perldo will run a Ruby or Perl one-liner on every line in a range (defaults to entire buffer), with $_ bound to the text of the current line (minus the newline). Manipulating $_ will change the text of that line.
You can use this to do certain things that are easy to do in a scripting language but not so obvious using Vim builtins. For example to reverse the order of the words in a line:
:perldo $_ = join ' ', reverse split
To insert a random string of 8 characters (A-Z) at the end of every line:
:rubydo $_ += ' ' + (1..8).collect{('A'..'Z').to_a[rand 26]}.join
You are limited to acting on one line at a time and you can't add newlines.
^O and ^I
Go to older/newer position.
When you are moving through the file (by searching, moving commands etc.) vim rember these "jumps", so you can repeat these jumps backward (^O - O for old) and forward (^I - just next to I on keyboard). I find it very useful when writing code and performing a lot of searches.
gi
Go to position where Insert mode was stopped last.
I find myself often editing and then searching for something. To return to editing place press gi.
gf
put cursor on file name (e.g. include header file), press gf and the file is opened
gF
similar to gf but recognizes format "[file name]:[line number]". Pressing gF will open [file name] and set cursor to [line number].
^P and ^N
Auto complete text while editing (^P - previous match and ^N next match)
^X^L
While editing completes to the same line (useful for programming).
You write code and then you recall that you have the same code somewhere in file. Just press ^X^L and the full line completed
^X^F
Complete file names.
You write "/etc/pass" Hmm. You forgot the file name. Just press ^X^F and the filename is completed
^Z or :sh
Move temporary to the shell. If you need a quick bashing:
press ^Z (to put vi in background) to return to original shell and press fg to return to vim back
press :sh to go to sub shell and press ^D/exit to return to vi back
Typing == will correct the indentation of the current line based on the line above.
Actually, you can do one = sign followed by any movement command. ={movement}
For example, you can use the % movement which moves between matching braces. Position the cursor on the { in the following code:
if (thisA == that) {
//not indented
if (some == other) {
x = y;
}
}
And press =% to instantly get this:
if (thisA == that) {
//not indented
if (some == other) {
x = y;
}
}
Alternately, you could do =a{ within the code block, rather than positioning yourself right on the { character.
" insert range ip's
"
" ( O O )
" =======oOO=(_)==OOo======
:for i in range(1,255) | .put='10.0.0.'.i | endfor
This is a nice trick to reopen the current file with a different encoding:
:e ++enc=cp1250 %:p
Useful when you have to work with legacy encodings. The supported encodings are listed in a table under encoding-values (see help encoding-values). Similar thing also works for ++ff, so that you can reopen file with Windows/Unix line ends if you get it wrong for the first time (see help ff).
imap jj <esc>
Let's see some pretty little IDE editor do column transposition.
:%s/\(.*\)^I\(.*\)/\2^I\1/
Explanation
\( and \) is how to remember stuff in regex-land. And \1, \2 etc is how to retrieve the remembered stuff.
>>> \(.*\)^I\(.*\)
Remember everything followed by ^I (tab) followed by everything.
>>> \2^I\1
Replace the above stuff with "2nd stuff you remembered" followed by "1st stuff you remembered" - essentially doing a transpose.
Not exactly a dark secret, but I like to put the following mapping into my .vimrc file, so I can hit "-" (minus) anytime to open the file explorer to show files adjacent to the one I just edit. In the file explorer, I can hit another "-" to move up one directory, providing seamless browsing of a complex directory structures (like the ones used by the MVC frameworks nowadays):
map - :Explore<cr>
These may be also useful for somebody. I like to scroll the screen and advance the cursor at the same time:
map <c-j> j<c-e>
map <c-k> k<c-y>
Tab navigation - I love tabs and I need to move easily between them:
map <c-l> :tabnext<enter>
map <c-h> :tabprevious<enter>
Only on Mac OS X: Safari-like tab navigation:
map <S-D-Right> :tabnext<cr>
map <S-D-Left> :tabprevious<cr>
Often, I like changing current directories while editing - so I have to specify paths less.
cd %:h
I like to use 'sudo bash', and my sysadmin hates this. He locked down 'sudo' so it could only be used with a handful of commands (ls, chmod, chown, vi, etc), but I was able to use vim to get a root shell anyway:
bash$ sudo vi +'silent !bash' +q
Password: ******
root#
I often use many windows when I work on a project and sometimes I need to resize them. Here's what I use:
map + <C-W>+
map - <C-W>-
These mappings allow to increase and decrease the size of the current window. It's quite simple but it's fast.
:r! <command>
pastes the output of an external command into the buffer.
Do some math and get the result directly in the text:
:r! echo $((3 + 5 + 8))
Get the list of files to compile when writing a Makefile:
:r! ls *.c
Don't look up that fact you read on wikipedia, have it directly pasted into the document you are writing:
:r! lynx -dump http://en.wikipedia.org/wiki/Whatever
Not an obscure feature, but very useful and time saving.
If you want to save a session of your open buffers, tabs, markers and other settings, you can issue the following:
mksession session.vim
You can open your session using:
vim -S session.vim
Map F5 to quickly ROT13 your buffer:
map <F5> ggg?G``
You can use it as a boss key :).
I use vim for just about any text editing I do, so I often times use copy and paste. The problem is that vim by default will often times distort imported text via paste. The way to stop this is to use
:set paste
before pasting in your data. This will keep it from messing up.
Note that you will have to issue :set nopaste to recover auto-indentation. Alternative ways of pasting pre-formatted text are the clipboard registers (* and +), and :r!cat (you will have to end the pasted fragment with ^D).
It is also sometimes helpful to turn on a high contrast color scheme. This can be done with
:color blue
I've noticed that it does not work on all the versions of vim I use but it does on most.
I just found this one today via NSFAQ:
Comment blocks of code.
Enter Blockwise Visual mode by hitting CTRL-V.
Mark the block you wish to comment.
Hit I (capital I) and enter your comment string at the beginning of the line. (// for C++)
Hit ESC and all lines selected will have // prepended to the front of the line.
I see console apps print colors and seen apps such as ffmpeg print text over itself instead of a new line. How do I print over an existing line? I want to display fps in my console app either at the very top or very bottom and have regular printfs go there and scroll normally.
I need this for windows, but this is meant to be cross platform, so I will eventually have a linux and mac implementation.
There is two simple possibilities which work on linux as well as windows, but only for one line:
printf("\b"); will return for one character, so you might count how many character you want to backspace and fire this in a loop, or you know that you only write n numbers and do it likeprintf("\b\b\b\b\b\b\b\b\b\b");
printf("text to be overwritten by next printf\r"); this will return the cursor to the beginning of the line, so any next printf will overwrite it. Make sure to write a string of same length or longer so you overwrite it entirely.
If you want to rewrite several lines, there is nothing so portable as ncurses, there is libs for it on practically every operating system, and you don't have to take care of the ANSI-differences.
edit: added link to ncurses wikipedia page, gives great overview and introduction, as well as link list and maybe a translation to your preferred language
Check out ncurses. It has bindings for most scripting languages.
You can use '\r' instead of '\n'.
The ASCII character number 8 (A.K.A. Ctrl-H, BS or Backspace) lets you back up one character. ASCII Character number 13 (A.K.A Ctrl-M, CR or Carriage Return) returns the cursor at the beggining of the line.
If you are working in C try putchar(8); and putchar(13);
The magic of the colors, cursor locating and bliking and so on are inside ANSI escape codes. Any text console capable of handling ANSI codes can use them just printing them out to console (i.e. by means of echo in a bash script or printf() function in C).
Unix terminals support ANSI escape sequences and Windows world used to support them back in old MS-DOS days, but the multibyte console support put an end to this. There is more information here. However there are other ways out of just ANSI sequences printing available on Windows. Moreover if you have Cygwin installed on your Windows maching ANSI codes work just as great as on any Unix terminal.
Many people mention Ncurses library that is the de-facto standard for any gui-like text based applications. What this library does is to hide all the terminal differences (Windows/Unix flavours) to represent the same information as identical as possible across all the platforms, though from my own experience I tell you this is not always true (i.e. typical text window frames change because the especial chars are not available under all character encodings). The counterpart of using ncurses is that it is a complete API and it is much harder to start out with it than simply writing out some ANSI escape sequences for simple things such as change the font color, cleaning screen or moving back the cursor to a random position.
For the sake of completeness I paste an example of use of ANSI sequence under Linux that changes the prompt to blue and shows the date:
PS1="\[\033[34m\][\$(date +%H%M)][\u#\h:\w]$ "
You can use Ncurses -
ncurses package is a subroutine library for terminal-independent screen-painting and input-event handling which presents a high level screen model to the programmer, hiding differences between terminal types and doing automatic optimization of output to change one screenfull of text into another
Depending on the platform which you are developing on there's probably a more powerful API which you could use, rather than old ASCII control codes.
e.g. If you are working on Win32 you can actually manipulate the console screen buffer directly.
A good place to start might be here
http://msdn.microsoft.com/en-us/library/ms683171(VS.85).aspx
I have been looking for similar functions/API which would allow me to access the console as something other than a stream of text for other platforms. Haven't found anything yet, but then again, I haven't been looking that hard.
Hope it helps.