The Big Programming Thread - Page 156

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1. This is not a "do my homework for me" thread. If you have specific questions, ask, but don't post an assignment or homework problem and expect an exact solution.
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3. If you can't articulate why a language is bad, don't start slinging shit about it. Just remember that nothing is worse than making CSS IE6 compatible.
4. Use [code] tags to format code blocks.

Dephy

Lithuania163 Posts

August 10 2012 10:19 GMT

#3101

i wanted to ask how to make stream link appear and dissapear from the list depeding if its on or off, like in TL? is there some short workaround? it shouldnt be hard?

EscPlan9

United States2777 Posts

August 12 2012 04:22 GMT

#3102

Without using any modules in Perl, I need to create a script that recursively traverses the directory and then output the total size of all the files and a few other statistics like the last modified file, etc. I have the recursion part somewhat down correctly in that everytime a directory is found the subroutine is called again to traverse that next directory, but the problem is it doesn't backtrack to the parent directories.

The pertinent section is below:

sub scanDir {
	my $curDir = shift;
		
	chdir($curDir) or die "Unable to change to dir $curDir: $!\n";
	opendir DIR, "." or die "Unable to open $curDir: $!\n";	
	my @contents = readdir(DIR) or die "Unable to read $curDir: $!\n";
	closedir(DIR);
		
	for (@contents) {
		# ignore the "." and ".." listings
		next if ($_ eq "." || $_ eq "..");
		
		if (-d "$_") {			
			evaluateFile($_);
			print "$_ is a dir of size " . $fileSize . " descending into...\n";			
			scanDir($_);
		}
		elsif (-f "$_") {
			evaluateFile($_);			
			print "$_ is a file, size = " . $fileSize . "\n";
		}		
	}
}

I'm trying to think of ways to make sure it runs through every subdirectory without any repetitions. The problem right now is once it finds a directory, it jumps into it and scans all the files and directories there, and it keeps doing that until no more directories are found. This means that in a directory with multiple subdirectories, only the first subdirectory is traversed through. It never returns through the other subdirectories.

From google searches I always see that people recommend using modules for this. My teacher wants us to tackle this problem without using modules though.

One possible method I can think of is creating a hash structure of Absolute-path-of-dir : Boolean (traversed or not). I would create new keys when new directories are found and update the values for the directories that I have traversed until all the keys -> values evaluate to True. While I think this might work, it'll be tricky and I feel like there must be a much simpler method I am missing. Any ideas?

supereddie

Netherlands151 Posts

August 12 2012 08:07 GMT

#3103

$_ is a global, so you'll probably run into weird stuff if you depend too much on it. Also, $fileSize seems to be global as well. Why don't you use it as a return from evaluateFile? Lastly, do you want the total size of a directory including subdirectorys? In that case you'll want to return the total size as well in scanDir.

EscPlan9

United States2777 Posts

August 12 2012 14:11 GMT

#3104

Yeah I cut off some of the code (like the evaluateFile subroutine). Yes, $fileSize is a global. You're right I can just use it as a return from evaluateFile. And finally, yes, the size of the directory and subdirectories themselves must be included.

I'm not sure what you mean by $_ is a global here. If I understand Perl's scope correctly, $_ scope is only within the for loop and gets assigned the value of the current element iterated through within the @contents array (listing of the directory).

EscPlan9

United States2777 Posts

August 12 2012 14:43 GMT

#3105

I figured it out. As I was thinking about possible problems with $_ (thanks for the suggestions supereddie), I decided to try passing the absolute path as the parameter this time rather than just the current path I was in (although I have only found out how to grab the absolute path by using the CWD module in Perl). I also took out the chdir line.

The changed portion:


sub scanDir {
	my $curDir = shift;
		
	opendir DIR, $curDir or die "Unable to open $curDir: $!\n";	
	my @contents = readdir(DIR) or die "Unable to read $curDir: $!\n";
	closedir(DIR);
		
	for (@contents) {
		# ignore the "." and ".." listings
		next if ($_ eq "." || $_ eq "..");
		
		if (-d "$curDir/$_") {			
			my $abs_path = abs_path("$curDir/$_");
			my $dirSize = evaluateFile("$abs_path");
			print "$abs_path" . " is a dir of size " . $dirSize . " descending into...\n";			
			scanDir("$abs_path");
		}
		elsif (-f "$curDir/$_") {
			my $fileSize = evaluateFile("$curDir/$_");			
			print "$_" . " is a file, size = " . $fileSize . "\n";
		}		
	}	
}

And if curious on the other subroutines and how it all comes together, full script in spoiler
+ Show Spoiler +


#!/usr/bin/perl
# dirwalk.pl

use strict;
use warnings;
use Cwd 'abs_path';			# module for Current Working Directory, evaluates absolute path

my $totalSize = 0;
my $lastModName = "";
my $lastModTime = 0;

# update totalSize, check for last modified and update if necessary
sub evaluateFile {
	my $fileName = $_[0];
	my @info = stat($fileName);
	my $bytes = $info[7];
	$totalSize += $bytes;
	
	my $epochModTime = $info[9];
	if ($epochModTime > $lastModTime) {
		$lastModTime = $epochModTime;		
		$lastModName = substr($fileName, rindex($fileName,"/")+1);
	}	
	
	return $bytes;
}

# open the directory and scan all the contents
sub scanDir {
	my $curDir = shift;
		
	opendir DIR, $curDir or die "Unable to open $curDir: $!\n";	
	my @contents = readdir(DIR) or die "Unable to read $curDir: $!\n";
	closedir(DIR);
		
	for (@contents) {
		# ignore the "." and ".." listings
		next if ($_ eq "." || $_ eq "..");
		
		if (-d "$curDir/$_") {			
			my $abs_path = abs_path("$curDir/$_");
			my $dirSize = evaluateFile("$abs_path");
			print "$abs_path" . " is a dir of size " . $dirSize . " descending into...\n";			
			scanDir("$abs_path");
		}
		elsif (-f "$curDir/$_") {
			my $fileSize = evaluateFile("$curDir/$_");			
			print "$_" . " is a file, size = " . $fileSize . "\n";
		}		
	}	
}

# validate parameter is a readable dir and only 1 argument passed
if ( !defined($ARGV[0]) || scalar @ARGV > 1 ) {
	print STDERR "Enter a directory\n";
	exit 1;
} elsif ( (!(-d $ARGV[0])) || (!(-r $ARGV[0])) ) {
	print STDERR "Enter a readable directory\n";
	exit 1;
}

scanDir($ARGV[0]);

print "Total size is " . $totalSize . " Bytes\n";
print "Last file modified was: " . $lastModName . "\n";
print "Last mod was " . $lastModTime . "\n";
print scalar localtime($lastModTime);	# easy conversion, but does not list timezone EDT

supereddie

Netherlands151 Posts

August 12 2012 16:59 GMT

#3106

Personall I would count the totalSize within the scanDir function and return it as a value. Something like:


sub scanDir {
    ....
    my $totalSize = 0;
    ....
    for .....
        $totalSize += scanDir if isDir;
        $totalSize += evaluateFile if isFile;
    ....
    print "total size (incl. subfolders) of dir " . $dirName . " = " . $totalSize . " bytes";
    return $totalSize;
}

....
print "Total size is " . scanDir($ARGV[0]) . " Bytes\n";

I feel like it would be easier to maintain/expand later on if needed.

EscPlan9

United States2777 Posts

August 12 2012 17:08 GMT

#3107

My professor is really specific with the formatting and instructions. He would mark off if I did something like that, though I understand what you're getting at. My output exactly matches his required now and I've submitted the script in the dropbox. Thanks for all the help!

SiPa

Germany129 Posts

August 13 2012 11:45 GMT

#3108

Quick Question:
I have a few lines of code, written in C++.
I have to write code, that does the same stuff in C.
the C++-code contains vectors (std::vector<>)
It uses the push_back-function and clear-function of the vector.
Is there an equivalent to the C++-vector in C? (Array with variable size?)
Google pretty much tells me to make my own thing.

Deleted User 101379

4849 Posts

August 13 2012 11:53 GMT

#3109

On August 13 2012 20:45 SiPa wrote:
Quick Question:
I have a few lines of code, written in C++.
I have to write code, that does the same stuff in C.
the C++-code contains vectors (std::vector<>)
It uses the push_back-function and clear-function of the vector.
Is there an equivalent to the C++-vector in C? (Array with variable size?)
Google pretty much tells me to make my own thing.

There is no equivalent. You can make your own implementation of a variable size array, though depending on the actual use, it might actually be easier to go with a linked list instead.

heishe

Germany2284 Posts

August 13 2012 11:59 GMT

#3110

There's not, but things without inheritance are convertible to C in a pretty straightforward manner (and inheritance is easy, too, just a bit bothersome), with some handicaps. But templates just won't work, you flat out won't be able to get that in C. So if you want multiple types to be handled by that vector, you either have to implement it multiple times each time for one certain type, or you have to store void* in the pointer and cast ("with certainty") around to get the types into and out of that you want. The rest works like this:

If you have some class with some method, e.g.


class vector
{
    attribute a;
    attribute b;
    attribute c;
    public:
         //...
        size_t size() 
        {
            //...
        }
}

it can be done by creating a struct vector and a free method size(vector* vec);


struct vector
{
   attribute a;
   attribute b;
   attribute c;
}

size_t size(vector *vec)
{
   //...
}

Similarly, methods with parameters would transform from return_type class::method(a,b,c) to return_type method(class*,a,b,c) (this is actually exactly like it looks in assembly code, without optimizations). Constructors can be implemented by simply making a free method Constructor[yourstructname](struct *str) or something.

Of course, usage changes too, from classobject.method(params); to method(&classobject,params);

Converting the vector class like this should be trivial, since you can look up its source code of whatever compiler/IDE you're using.

However, you can not recreate other built-in features to C++ like RAII, unfortunately.

waxypants

United States479 Posts

August 14 2012 02:05 GMT

#3111

Not in standard C. I like to use glib for generic data structures among other things.

http://developer.gnome.org/glib/stable/glib-data-types.html
http://developer.gnome.org/glib/stable/

Olsson

Sweden931 Posts

August 15 2012 12:41 GMT

#3112

Does anyone know a good website to learn C#? You guys got me interested, I tried C++ abit but I think it was too much like most of you guys told me.

bo1b

Australia12814 Posts

August 15 2012 19:02 GMT

#3113

I just noticed a new edition of c++ primer was released, does anyone think it would be a good idea to buy it or are they're better resources for learning c++?

IreScath

Canada521 Posts

August 15 2012 20:38 GMT

#3114

edit: nvm... I figured it out.

tofucake

Hyrule19264 Posts

August 15 2012 20:40 GMT

#3115

I'm sure this doesn't really help you at all but personally I hate handbrake.

...yeah

IreScath

Canada521 Posts

August 15 2012 20:53 GMT

#3116

On August 16 2012 05:40 tofucake wrote:
I'm sure this doesn't really help you at all but personally I hate handbrake.

...yeah

open scource + opencl = yay.

but I think I go it now.

SiPa

Germany129 Posts

August 16 2012 09:02 GMT

#3117

GLib is awesome!
Now some questions regarding GLib:
I get tons of "expression must be an lvalue or a function designator" and "a nonstatic member reference must be relative to a specific object" errors. I get, that this isnt necessarily connected to GLib, so i will just give you the code:

	struct trajectory{
	GArray *position1;
	GArray *position2;
	GArray *velocity1;
	GArray *velocity2;
	position1 = g_array_new(FALSE, FALSE, sizeof (double));
	velocity1 = g_array_new(FALSE, FALSE, sizeof (double));
	position2 = g_array_new(FALSE, FALSE, sizeof (GArray));
	velocity2 = g_array_new(FALSE, FALSE, sizeof (GArray));
	_Fragment fragment;
	};

	
	GArray *startVelocity;
	startVelocity = g_array_new(FALSE, FALSE, sizeof(double));
	g_array_append_val(startVelocity, g_array_index(iDir, double, 0) * iFragment.Speed);
	g_array_append_val(startVelocity, g_array_index(iDir, double, 1) * iFragment.Speed);
	g_array_append_val(startVelocity, g_array_index(iDir, double, 2) * iFragment.Speed);

	g_array_free(trajectory.velocity2, TRUE);
	g_array_append_val(trajectory.velocity2, startVelocity);
	g_array_free(trajectory.position2, TRUE);
	g_array_append_val(trajectory.position2, iPos);

iPos and iDir are pointers to GArrays.

 trajectory calcTrajectory( _Fragment iFragment, GArray *iPos, GArray *iDir ){}

Errors are at g_array_append_val, velocity2, position2

I hope some1 could provide help, thx in advance!

Edit: I also would love to know how to get the size of a GArray, meaning how many Elements it contains.

waxypants

United States479 Posts

August 17 2012 03:18 GMT

#3118

Don't have time to figure out what you are trying to do right now, but I can tell you:

1)

position1 = g_array_new(FALSE, FALSE, sizeof (double));

In C, you can't have member initialization inside the struct definition.

2)

trajectory.velocity2

In C, you can't have static struct members.

waxypants

United States479 Posts

August 17 2012 03:50 GMT

#3119

This is a response to a PM about where to get Glib. I put installation instructions for Visual Studio. These instructions are actually pretty much the same for most of the "open source" projects you may want to download and use with Visual Studio. Let me know if it doesn't work and I will try to fix my instructions if I left something out or something.

You can build it yourself (enormous pain), or get it from here:

http://www.gtk.org/download/win32.php

Not the newest version, but fairly recent. You may be able to find a newer version elsewhere but this one has worked well enough for me.

I'm assuming you are using Visual Studio. In that case you will need to do the following:

To build your program:
1) Download the Glib "Dev".
2) Extract it to something like C:\glib-dev_2.28.8-1_win32 (or whatever directory you want)
3) In your project properties, go to Configuration Properties->C/C++->General and add "C:\glib-dev_2.28.8-1_win32\lib\glib-2.0\include" and "C:\glib-dev_2.28.8-1_win32\include\glib-2.0" to the list of Additional Include Directories.
4) In your project properties, go to Configuration Properties->Linker->General and add "C:\glib-dev_2.28.8-1_win32\lib" to your list of Additional Library Directories.
5) In your project properties, go to Configuration Properties->Linker->Input and add "glib-2.0.lib" to your list of Additional Dependencies.

For steps 3 and 5 you may need to add other directories and/or other lib files to the list, but these things have been enough for what I have done. You will know what you need to add whenever it complains that it can't find "blahblah.h" or "blahblah.lib".

To run your program:
1) Download the Glib "Run-time"
2) Extract whatever files you need from the bin directory into the same directory as your program's exe file. You can add one at a time until your program is able to run, or you can just copy all of them if you don't care about having extra unnecessary files. In theory, I think could also put them in C:\Windows\System32 if you want, and then you won't have to copy them to all of your projects, but if somebody else wants to run your program they will need to download the necessary dll's.

waxypants

United States479 Posts

August 17 2012 11:23 GMT

#3120

The lvalue error is because the second argument in g_array_append_val has to have an address (in other words it has to be a variable). It's because it seems that they have defined g_array_append_val as:

#define g_array_append_val(a,v)	  g_array_append_vals (a, &(v), 1)

The &(v) is what is throwing the error. Anyway it sucks, but you can do something like:

double speed;

speed = g_array_index(iDir, double, 0) * iFragment.Speed;
g_array_append_val(startVelocity, speed);
speed = g_array_index(iDir, double, 1) * iFragment.Speed;
g_array_append_val(startVelocity, speed);
speed = g_array_index(iDir, double, 2) * iFragment.Speed;
g_array_append_val(startVelocity, speed);

Or even:

double speeds[3];

speeds[0] = g_array_index(iDir, double, 0) * iFragment.Speed;
speeds[1] = g_array_index(iDir, double, 1) * iFragment.Speed;
speeds[2] = g_array_index(iDir, double, 2) * iFragment.Speed;
g_array_append_vals(startVelocity, speeds, 3);

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