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Top Forums Programming Newline in ANSI-C standard functions Post 303020299 by yifangt on Monday 16th of July 2018 11:49:35 AM
Old 07-16-2018
Thanks Jim and Corona:
I was not sure the NULL terminator was handled correctly.
If str1 precedes str2 in memory and each one is word-aligned, then the last character you write to str1[128] effectively cause the end of of str1 to be the actual end of str2. This is quite twisting to me!! Now my understanding come to this:

1) Doing strncpy() first caused no NUL terminator, and gave me buffer overflow and strcpy() could not run at all.
2) Instead, doing strcpy() first the correct NUL terminator is ensured, then the following strncpy() seems working which still does not provide NUL terminator. But, because the program exits, just the problem did not show up.

Is this correct?
Blindly using strncpy because people call strcpy "bad" is worse than just using strcpy in the first place.

I do not know the risk of strcpy() or the correct use of strncpy(). They just happened to come to my exercise. I thought figure out the details may help understanding what's going on in the memory, which is why I tried memset(). Thanks again.

Last edited by yifangt; 07-16-2018 at 01:06 PM..
 

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XTERMCONTROL(1) 						   User Commands						   XTERMCONTROL(1)

NAME
xtermcontrol - dynamic control of XFree86 xterm properties. SYNOPSIS
xtermcontrol [OPTIONS]... DESCRIPTION
xtermcontrol makes it easy to change colors, title, font and geometry of a running XFree86 xterm(1), as well as to report the current set- tings of the aforementioned properties. Window manipulations de-/iconify, raise/lower, maximize/restore and reset are also supported. To complete the feature set; xtermcontrol lets advanced users issue any xterm control sequence of their choosing. OPTIONS
--fg=COLOR Set foreground color (see also COLOR NAMES). --bg=COLOR Set background color. --colorN=COLOR Set N'th [0-15] color. --highlight=COLOR Set highlight color. --cursor=COLOR Set cursor color. --mouse-fg=COLOR Set mouse pointer foreground color. --mouse-bg=COLOR Set mouse pointer background color. --font=FONT Set font name (see also FONT NAMES). Alternatively it is possible to specify a fontmenu index as '#[0-6]' or navigate the fontmenu by relative sizes as '#+N' or '#-N', where N is an optional integer. --title=STRING Set window title. Note that mechanisms like the bash(1) PROMPT_COMMAND may overwrite the title. --geometry=WIDTHxHEIGHT+XOFF+YOFF Set size and/or position. Through its control sequences the xterm only recognize positive XOFF and YOFF offsets, which are pixels relative to the upper left hand corner of the display. xtermcontrol is therefore unable to handle negative offsets as described in the X(7x) GEOMETRY SPECIFICATIONS and therefore truncates negative values to zero. --get-fg Report foreground color. --get-bg Report background color. --get-colorN Report N'th [0-15] color. --get-highlight Report highlight color. --get-cursor Report cursor color. --get-mouse-fg Report mouse pointer foreground color. --get-mouse-bg Report mouse pointer background color. --get-font Report font. --get-title Report window title. --get-geometry Report size and position. The size of the text area is reported in characters and the position is reported in pixels relative to the upper left hand corner of the display. --maximize Maximize window. --restore Restore maximized window. --iconify Iconify window. --de-iconify De-iconify window. --raise Raise window. --lower Lower window. --reset Full reset. --raw=CTLSEQS Issue raw control sequence (see also XTERM CONTROL SEQUENCES). --file=FILE Force xtermcontrol to read configurations (see also CONFIGURATION) from FILE instead of the standard personal initialization file ~/.xtermcontrol. --force, -f Skip TERM environment variable check. --verbose, -v Print verbose reports. --help, -h Print help message and exit. --version Print the version number and exit. CONFIGURATION
xtermcontrol reads a default, ~/.xtermcontrol, or a user specified configuration file on startup. Each line in the file is either a com- ment or contains an attribute. Attributes consist of a keyword and an associated value: keyword = value # comment The valid keyword/value combinations are: foreground="COLOR" background="COLOR" highlight="COLOR" cursor="COLOR" mouse-foreground="COLOR" mouse-background="COLOR" geometry="WIDTHxHEIGHT+XOFF+YOFF" font="FONT" color0="COLOR" color1="COLOR" color2="COLOR" color3="COLOR" color4="COLOR" color5="COLOR" color6="COLOR" color7="COLOR" color8="COLOR" color9="COLOR" color10="COLOR" color11="COLOR" color12="COLOR" color13="COLOR" color14="COLOR" color15="COLOR" Whitespace is ignored in attributes unless within a quoted value. The character '#' is taken to begin a comment. Each '#' and all remaining characters on that line is ignored. FONT NAMES
xtermcontrol accepts any X(7x) FONT NAMES. Font names like '-adobe-courier-medium-r-normal--10-100-75-75-m-60-iso8859-1' are very cumber- some to write, so it is convenient to make use of aliases, e.g. 'fixed' or '8x13', if present in fonts.alias files of the font directo- ries. COLOR NAMES
xtermcontrol accepts any X(7x) COLOR NAMES. Basically this means that colors are specified by name or rgb value, e.g. 'blue', 'rgb:0000/0000/FFFF' or '#00F'. Colors are typically reported by the xterm in a device-dependent numerical form, e.g. 'rgb:0000/0000/FFFF'. Note that old syntax rgb values should always be quoted to avoid '#' being interpreted as the beginning of a comment by the shell (see also FILES). XTERM CONTROL SEQUENCES
The secret behind xtermcontrol is xterm control sequences. All the possible (there are a plethora of them) control sequences are documented in ctlseqs.txt, found in the xterm(1) distribution (see also FILES). TROUBLESHOOTING
If read/write permissions on the tty's are changed so that special group membership is required to be able to write to the pseudo terminal, the easiest workaround is to install xtermcontrol setuid root. Xterm(1) has three resources, allowWindowOps, allowTitleOps, and allowFontOps, that enables or disables special operations which xtermcon- trol relies on. If any of these resources are set (or defaults) to 'false' xtermcontrol may hang. The resources corresponds to xtermcon- trol options as: allowWindowOps: --raise --lower --restore --maximize --iconify --de-iconify --get-title --geometry --get-geometry allowTitleOps: --title allowFontOps: --font --get-font All three resources can usually be enabled for the current xterm session via a menu; ctrl+rightclick and look for menu item names like 'Allow Window Ops'. To set these resource values persistently you can add the following to either your local ~/.Xdefaults file, or to a system-wide resource file like /etc/X11/app-defaults/XTerm: *VT100.allowWindowOps: true *VT100.allowTitleOps: true *VT100.allowFontOps: true FILES
<XRoot>/X11/rgb.txt Default rgb color name file location. ctlseqs.txt Xterm control sequences documentation. Distributed with xterm from http://dickey.his.com/xterm/ SEE ALSO
xterm(1), X(7x) COPYRIGHT
Copyright (C) 2002-2009 Jess Thrysoee <jess@thrysoee.dk> xtermcontrol 2.10 October 17, 2009 XTERMCONTROL(1)
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