basilevsthecat

FolderSize

2009-09-18T03:52:34Z

Most experienced Windows users use file manager different from built in Explorer. Today I've found a plugin that brings Windows Explorer closer to those advanced file managers.

FolderSize plugin adds a new column in Explorers table view. This column shows amount of space on disk occupied by file or folder, its subfolders and files.

I give my thanks to free4you-yohunza for giving me a tip.

bzip2 and boost

2009-08-18T05:26:23Z

Half year nightmare has finally ended yesterday.

Long time ago a SEGV (segmentation violation, memory handling error) appeared in my C++ program that I write as a hobby. As program used many external libraries (libxml2, bzip2, sqlite and others) quest for source of this error has taken half a year cost of my free time and my youth away.

Last week I've completed writing of test suite for some components of project in question. Tests were failing as often as main project binary, but splitting them into more specific ones has finally revealed the source of error. Boost::iostreams::bzip2_decompressor was the culprit! I've posted a description of the error on boost tracking system.

In short, boost::iostreams filters bzip2_decompressor and bzip2_compressor act just fine when used after creation, but their destructor handle things carelessly when executing on unused, freshly created instances.

Write unit tests! Be happy!

Люди способны к эхолокации

2009-07-01T13:35:57Z

Люди способны к эхолокации. Разрешение "изображения" получаемого некоторыми из слепых людей с помощью эхолокации может быть неожиданно высоким.

Популярную адаптациию статьи на эту тему можно почитать в журнале Компьюлента. Статья сопровождается впечатляющим видеоматериалом.

Ultimate video simplifier

2009-06-25T07:20:11Z

To view a video encoded with modern codec on older computers decrease bitarates and simplify format using mencoder.


sudo echo "deb http://www.debian-multimedia.org/ testing main" >> /etc/apt/sources.list.d/multimedia.list
sudo apt-get update
sudo apt-get install mencoder
mencoder -oac copy -ovc lavc -lavcopts vcodec=mpeg2video from.avi -o to.avi

View latest logs

2009-04-14T06:04:25Z

On linux, I'm viewing lately modified logs with the following command:

find /var/log -mmin -10 |xargs less ++G

This approach combines a power of less and find. Find allows searching files by various criteria, less provides basic viewing capability and simple navigation.

Short explanation:

find - finds files
/var/log - a path to search in
-mmin -10 - found files should be modified less than 10 minutes ago
xargs - convert stdin into arguments of the given command
less - view files
first + - execute an internal less command
second + - execute the given command on each file
G - an internal less command "jump to the end"

Less viewer allows navigation between files in arguments. To go forward, input ":n", to go backward input ":p".

find xargs and less have so many possible parameters, that reading their manuals might be a pain. I'd recommend a novice not to bother reading them all, but use man(less) search feature (input "/" to start search in man viewer).

If files in the inspected folder have complex names with spaces or quotes, use

find /var/log -mmin -10 -print0 | xargs -0 less ++G

-print0 will make find separate filenames with zero characters, while -0 causes xargs no use for splitiing any other character except null one.

If you don't need to abort viewing in the middle of sequence, or navigate backward, you may use:

find /var/log -mmin -10 -print0 | xargs -0 -n1 less ++G

or, almost equivalent:

find /var/log -mmin -10 -print0 -exec less ++G '{}' \;

In this case you proceed to next file by pressing "q".

I'd like to thank Alexey Buzykaev, who explained accurate way of using xargs.

How to interpret typeid.name()

2009-02-04T15:19:13Z

There is often a need to print type information in debug messages. The only correct way to get dynamic type information in C++ - typeid(object).name(). Unfortunately, it returns an internal representation (type names are mangled) of type that is hard to read.

Here is a self-explanatory C function that returns a full type of it's argument as a string.
May be regarded as abi::__cxa_demangle manual.


#include <stdexcept>
#include <cxxabi.h>
#include <string>

// Please, don't use this code for commercial purpose.

template <class T>
std::string typeOf(T& object) throw(std::logic_error, std::bad_alloc) {
	using namespace std;
	int status;
	string rawTypeName=typeid(object).name();
	char *name = abi::__cxa_demangle(rawTypeName.c_str(), 0, 0, &status);
	string retvalue;
	if (name!=NULL) {
		retvalue=name;
		free(name);
	}
	switch (status) {
	case 0: //Succeed
		return retvalue;
	case -1: //Memory allocation error
		throw bad_alloc();
	case -2: //Invalid name
		return rawTypeName;
	case -3: //Invalid argument
		throw invalid_argument(string("Invalid argument while demangling ")+rawTypeName);
	default:
		throw logic_error(string("Unknown error while demangling ")+rawTypeName);
	}
}

Контролируемые ядерные реакции

2009-01-29T12:53:29Z

Ядерная энергетика обладая рядом неоспоримых преимуществ перед сжиганием органического топлива, тем не менее имеет фатальный недостаток - отработанное ядерное топливо очень опасно из-за долгоживущих радиоактивных изотопов, с периодом полураспада в сотни лет. Из-за цены особых методик захоронения, обеспечивающих относительно безопасное хранение отработанного ядерного топлива, стоимость ядерной энергии сравнима со стоимостью энергии газовых электростанций.
Термоядерные реакторы, идеальный источник энергии будущего, лишены этих недостатков, но пока никак не могут выйти на КПД больший единицы.

И вот популярное описание проекта, который одновременно решает проблемы ядерной и термоядерной энергетик.

Авторы предлагают поместить в центре большого объема отработанного ядерного топлива небольшой термоядерный реактор. Используя последний как источник нейтронов, можно катализировать ядерные распады в отработанном топливе, заставить его распадаться, а получаемую энергию использовать. При потоке нейтронов достаточной плотности, после обработки в такой установке, ядерное топливо станет значительно безопаснее - уменьшится содержание долгоживущих опасных изотопов.

В нашем НИИ тоже недавно был семинар про источник нейтронов для контролируемых ядерных реакций. Теперь жалею, что не сходил послушать.

A logging library for bash scripts

2008-10-02T15:08:16Z


#!/bin/bash
# A logging library
# Supports a test for the same message (see put_changed_report)


# Appends to a variable which name given in first argument all other arguments.
# Arguments: message_var a string to append 
function append () {
	local name=$1 val
	eval val=\$$name
	shift
	if [[ "$val" == "" ]]; then 
		eval $name=\"'$@'\"
	else 
		eval $name=\"'$val' '$@'\"
	fi
}

# Prints a complete report line
# Format: date time \t message \r\n
# Special EOL escaping is needed for the log to be correctly viewed by Microsoft programs.
# Arguments: message 
function make_report () {
	echo -en `date --rfc-3339=seconds`\\t$@ \\r\\n
}

# Removes Microsoft EOL escaping
function unescape () {
	echo "$@" | awk '{gsub(/[\n\r]/, ""); gsub(/ *$/, ""); print $0;}'
}

# For each line of log from input prints message without time and eols
# A reverse of make_report
function parse_report () {
	local date_time message IFS
	IFS=`echo -en \\\t`
	while read date_time message ; do
		echo `unescape $message`
	done
}

# Prints last logged message 
# Arguments: log_file
function last_message() {
	local log_file=$1
	tail -n 1 "$log_file" | parse_report
}

# Adds a report to a file
# Doesn't add a report if a previous one has the same message.
#Arguments: log_file message
function put_changed_report() {
	local logfile=$1
	shift
	local current="$@"
	if [[ -z "$current" ]] ; then
		return
	fi
	local prev=`last_message "$logfile"`
	if [[ "$prev" != "$current" ]] ; then 
		make_report $current >> "$logfile" 
	fi
}