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• Problem using the find function in MATLAB

  - by Peter Etchells

  I have two arrays of data that I'm trying to amalgamate. One contains actual latencies from an experiment in the first column (e.g. 0.345, 0.455... never more than 3 decimal places), along with other data from that experiment. The other contains what is effectively a 'look up' list of latencies ranging from 0.001 to 0.500 in 0.001 increments, along with other pieces of data. Both data sets are X-by-Y doubles. What I'm trying to do is something like... for i = 1:length(actual_latency) row = find(predicted_data(:,1) == actual_latency(i)) full_set(i,1:4) = [actual_latency(i) other_info(i) predicted_info(row,2) ... predicted_info(row,3)]; end ...in order to find the relevant row in predicted_data where the look up latency corresponds to the actual latency. I then use this to created an amalgamated data set, full_set. I figured this would be really simple, but the find function keeps failing by throwing up an empty matrix when looking for an actual latency that I know is in predicted_data(:,1) (as I've double-checked during debugging). Moreover, if I replace find with a for loop to do the same job, I get a similar error. It doesn't appear to be systematic - using different participant data sets throws it up in different places. Furthermore, during debugging mode, if I use find to try and find a hard-coded value of actual_latency, it doesn't always work. Sometimes yes, sometimes no. I'm really scratching my head over this, so if anyone has any ideas about what might be going on, I'd be really grateful.

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• comma separated values in oracle function body

  - by dmitry

  I've got following oracle function but it does not work and errors out. I used Ask Tom's way to convert comma separated values to be used in select * from table1 where col1 in <> declared in package header: TYPE myTableType IS table of varchar2 (255); Part of package body: l_string long default iv_value_with_comma_separated|| ','; l_data myTableType := myTableType(); n NUMBER; begin begin LOOP EXIT when l_string is null; n := instr( l_string, ',' ); l_data.extend; l_data(l_data.count) := ltrim( rtrim( substr( l_string, 1, n-1 ) ) ); l_string := substr( l_string, n+1 ); END LOOP; end; OPEN my_cursor FOR select * from table_a where column_a in (select * from table (l_data)); CLOSE my_cursor END; above fails but it works fine when I remove select * from table (l_data) Can someone please tell me what I might be doing wrong here??

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• Prototype function to set onclick event observer in checkboxes

  - by xain

  Hi, I want to set an observer for each of the following checkboxes: <div id="listr"> <ul id="lr" style="list-style-type: none"> <p class="tir">Text 1</p> <li class="ro"><input type="checkbox" name="r1" id="r1"/>A1</li> <li class="ro"><input type="checkbox" name="r2" />A2</li> <p class="tir">Text 2</p> <li class="rubro"><input type="checkbox" name="r3" />B1</li> <p class="tir">Text 3</p> <li class="ro"><input type="checkbox" name="r4" />B2</li> </ul> </div> It works if I write one observer per checkbox, but I want to do it in a short fashion, so I need something like $$('listr.lr.li.input').invoke('observe',click,function(field) { alert(this.name + ' clicked ' + this.checked); // other stuff ... }); Which is not working Thanks in advance

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• SWIG interface to receive an opaque struct reference in Java through function argument

  - by Beeo

  I am trying to use SWIG in order to use the Spotify API (libspotify) for Android: https://developer.spotify.com/technologies/libspotify/ I am having trouble defining the SWIG interface file to be able to successfully call the following native C function: sp_error sp_session_create(const sp_session_config * config, sp_session ** sess); Which in C would be called like this: //config struct defined previously sp_session *sess; sp_session_create(&config, &sess); But in Java I would need to call it like this: //config object defined previously sp_session javaSess = new sp_session(); sp_session_create(config, javaSess); sp_session is an opaque struct and is only defined in libspotify's API.h file as: typedef struct sp_session sp_session; I'm expecting the libspotify library to create it and give me a reference to it. The only thing I need that reference for then is to pass to other functions in the API. I believe the answer lies within the SWIG interface and typemaps, but I have been unsuccessful in trying to apply the examples I found in the documentation: http://www.swig.org/Doc2.0/SWIGDocumentation.html#Java_struct_pointer_pointer `http://www.swig.org/Doc2.0/SWIGDocumentation.html#Java_using_typemaps_return_arguments Help!

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• Adding an Array inside an array in a PHP function

  - by bateman_ap

  I have created a function in PHP that calls a webservice and parses through the result, assinging values to variables and returning them all as an Array. This all works perfectly, however I have come across a need to have an "array within my array" I am assigning values as below: $productName = $product->Name; $productID = $product->ID; $productArray = array( 'productName' => "$productName", 'productID' => "$productID" ); return $productArray; However I now have a piece of data that comes back with multiple results so I need to have a additional array to store these, I am getting the values from the returned XML using a foreach loop, however I want to be able to add them to the array with a name so I can reference them in the returned data, this is where I have a problem... $bestForLists = $product->BestFors; foreach( $bestForLists as $bestForList ) { $productBestFors = $bestForList->BestFor; foreach( $productBestFors as $productBestFor ) { $productBestForName = $productBestFor->Name; $productBestForID = $productBestFor->ID; } } I tried creating an array for these using the below code: $bestForArray[] = (array( "productBestForID" => "$productBestForID", "productBestForName" => "$productBestForName" )); And then at the end merging these together: $productArray= array_merge($productArray,$bestForArray); If I print out the returned value I get: Array ( [productName] => Test Product [productID] => 14128 [0] => Array ( [productBestForID] => 56647 [productBestForName] => Lighting ) [1] => Array ( [productBestForID] => 56648 [productBestForName] => Sound ) ) I would like to give the internal Array a name so I can reference it in my code, or is there a better way of doing this, at the moment I am using the following in my PHP page to get values: $productName = $functionReturnedValues['productName']; I would like to use the following to access the array I could then loop through: $bestForArray = $functionReturnedValues['bestForArray']; Hope someone can help

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• Parsing HTML: Call to a member function > children() on a non-object

  - by sm56d

  Hello all, I was just helped with this question but I can't get it to move to the next block of HTML. $html = file_get_html('http://music.banadir24.com/singer/aasha_abdoo/247.html'); $urls = $html->find('table[width=100%] table tr'); foreach($urls as $url){ $song_name = $url->children(2)->plaintext; $url = $url->children(6)->children(0)->href; } It returns the list of the names of the first album (Deesco) but it does not continue to the next album (The Best Of Aasha)? It just gives me this error: Notice: Trying to get property of non-object in C:\wamp\www\test3.php on line 26 Fatal error: Call to a member function children() on a non-object in C:\wamp\www\test3.php on line 28 Why is this and how can I get it to continue to the next table element? I appreciate any help on this! Please note: This is legal as the songs are not bound by copyright and they are available to download freely, its just I need to download a lot of them and I can't sit there clicking a button all day. Having said that, its taken me an hour to get this far.

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• Best solution for an StringToInt function in C#

  - by StefanE

  Hi, I were asked to do an StringToInt / Int.parse function on the white board in an job interview last week and did not perform very good but I came up with some sort of solution. Later when back home I made one in Visual Studion and I wonder if there are any better solution than mine below. Have not bothred with any more error handling except checking that the string only contains digits. private int StrToInt(string tmpString) { int tmpResult = 0; System.Text.Encoding ascii = System.Text.Encoding.ASCII; byte[] tmpByte = ascii.GetBytes(tmpString); for (int i = 0; i <= tmpString.Length-1; i++) { // Check whatever the Character is an valid digit if (tmpByte[i] > 47 && tmpByte[i] <= 58) // Here I'm using the lenght-1 of the string to set the power and multiply this to the value tmpResult += (tmpByte[i] - 48) * ((int)Math.Pow(10, (tmpString.Length-i)-1)); else throw new Exception("Non valid character in string"); } return tmpResult; }

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• Using a function found in a different file in a loop

  - by Anders

  This question is related to BuddyPress, and a follow-up question from this question I have a .csv-file with 790 rows and 3 columns where the first column is the group name, second is the group description and last (third) the slug. As far as I've been told I can use this code: <?php $groups = array(); if (($handle = fopen("groupData.csv", "r")) !== FALSE) { while (($data = fgetcsv($handle, 1000, ",")) !== FALSE) { $group = array('group_id' = 'SOME ID', 'name' = $data[0], 'description' = $data[1], 'slug' = groups_check_slug(sanitize_title(esc_attr($data[2]))), 'date_created' = gmdate( "Y-m-d H:i:s" ), 'status' = 'public' ); $groups[] = $group; } fclose($handle); } foreach ($groups as $group) { groups_create_group($group); } With http://www.nomorepasting.com/getpaste.php?pasteid=35217 which is called bp-groups.php. The thing is that I can't make it work. I've created a new file with the code written above called groupgenerator.php uploaded the .csv file to the same folder and opened groupgenerator.php in my browser. But, i get this error: Fatal error: Call to undefined function groups_check_slug() in What am I doing wrong?

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• C# function called after dependency property have been set

  - by mizipzor

  My code currently looks like this: private Foo myFoo; public Foo CurrentFoo { get { return myFoo; } set { SetFoo(value); } } private void SetFoo(Foo newFoo) { // Do stuff // Here be dragons myFoo = newFoo; } To be able to bind it in XAML/WPF I need to turn Foo into a dependency property: public static DependencyProperty CurrentFooProperty = DependencyProperty.Register("CurrentFoo", typeof(Foo), typeof(FooHandler), new PropertyMetadata(false)); public Foo CurrentFoo { get { return (Foo)GetValue(CurrentFooProperty); } set { SetValue(CurrentFooProperty, value); } } Ive heard that you shouldnt do magic inside the actual C# property set {}, since it might not be called but the value is written directly to the dependency property. If this is false, let me know, it seems like the most obvious and simple route to take. I know I can add a validation function to the dependency property but I assume that it shouldnt be used for this? I need to communicate the change to legacy systems that cannot yet be bound in XAML. Whats the best way to approach this problem?

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• Execute a function to affect different template class instances

  - by Samer Afach

  I have a complicated problem, and I need help. I have a base case, class ParamBase { string paramValue; //... } and a bunch of class templates with different template parameters. template <typename T> class Param : public ParamBase { T value; //... } Now, each instance of Param has different template parameter, double, int, string... etc. To make it easier, I have a vector to their base class pointers that contains all the instances that have been created: vector<ParamBase*> allParamsObjects; The question is: How can I run a single function (global or member or anything, your choice), that converts all of those different instances' strings paramValue with different templates arguments and save the conversion result to the appropriate type in Param::value. This has to be run over all objects that are saved in the vector allParamsObjects. So if the template argument of the first Param is double, paramValue has to be converted to double and saved in value; and if the second Param's argument is int, then the paramValue of the second has to be converted to int and saved in value... etc. I feel it's almost impossible... Any help would be highly appreciated :-)

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• tiemout for a function that waits indefiinitely (like listen())

  - by Fantastic Fourier

  Hello, I'm not quite sure if it's possible to do what I'm about to ask so I thought I'd ask. I have a multi-threaded program where threads share a memory block to communicate necessary information. One of the information is termination of threads where threads constantly check for this value and when the value is changed, they know it's time for pthread_exit(). One of the threads contains listen() function and it seems to wait indefinitely. This can be problematic if there are nobody who wants to make connection and the thread needs to exit but it can't check the value whether thread needs to terminate or not since it's stuck on listen() and can't move beyond. while(1) { listen(); ... if(value == 1) pthread_exit(NULL); } My logic is something like that if it helps illustrate my point better. What I thought would solve the problem is to allow listen() to wait for a duration of time and if nothing happens, it moves on to next statement. Unfortunately, none of two args of listen() involves time limit. I'm not even sure if I'm going about the right way with multi-threaded programming, I'm not much experienced at all. So is this a good approach? Perhaps there is a better way to go about it? Thanks for any insightful comments.

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• Invoking a function (main()) from a binary file in C

  - by Dhara Darji

  I have simple c program like, my_bin.c: #include <stdio.h> int main() { printf("Success!\n"); return 0; } I compile it with gcc and got executable: my_bin. Now I want to invoke main (or run this my_bin) using another C program. That I did with mmap and function pointer like this: #include <stdio.h> #include <fcntl.h> #include <sys/mman.h> int main() { void (*fun)(); int fd; int *map; fd = open("./my_bin", O_RDONLY); map = mmap(0, 8378, PROT_READ, MAP_SHARED, fd, 0); fun = map; fun(); return 0; } PS: I went through some tutorial, for how to read binary file and execute. But this gives Seg fault, any help appreciated! Thanks!

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• Replace without the replace function

  - by Molly Potter

  Assignment: Let X and Y be two words. Find/Replace is a common word processing operation that finds each occurrence of word X and replaces it with word Y in a given document. Your task is to write a program that performs the Find/Replace operation. Your program will prompt the user for the word to be replaced (X), then the substitute word (Y ). Assume that the input document is named input.txt. You must write the result of this Find/Replace operation to a file named output.txt. Lastly, you cannot use the replace() string function built into Python (it would make the assignment much too easy). To test your code, you should modify input.txt using a text editor such as Notepad or IDLE to contain different lines of text. Again, the output of your code must look exactly like the sample output. This is my code: input_data = open('input.txt','r') #this opens the file to read it. output_data = open('output.txt','w') #this opens a file to write to. userStr= (raw_input('Enter the word to be replaced:')) #this prompts the user for a word userReplace =(raw_input('What should I replace all occurences of ' + userStr + ' with?')) #this prompts the user for the replacement word for line in input_data: words = line.split() if userStr in words: output_data.write(line + userReplace) else: output_data.write(line) print 'All occurences of '+userStr+' in input.txt have been replaced by '+userReplace+' in output.txt' #this tells the user that we have replaced the words they gave us input_data.close() #this closes the documents we opened before output_data.close() It won't replace anything in the output file. Help!

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• Appending a function to an existing onclick event at page load

  - by tonsils

  Hi, I have the following html code that is pre written by the app I am using, which I do not have access to, i.e. <td align="center" class="shuttleControl"> <img src="/i/mydb/icons/shuttle_reload.png" onclick="g_Shuttlep_v61.reset();" alt="Reset" title="Reset"/> <img src="/i/mydb/icons/shuttle_last.png" onclick="g_Shuttlep_v61.move_all();" alt="Move All" title="Move All"/> <img src="/i/mydb/icons/shuttle_right.png" onclick="g_Shuttlep_v61.move();" alt="Move" title="Move" /> <img src="/i/mydb/icons/shuttle_left.png" onclick="g_Shuttlep_v61.remove();" alt="Remove" title="Remove" /> <img src="/i/mydb/icons/shuttle_first.png" onclick="g_Shuttlep_v61.remove_all();" alt="Remove All" title="Remove All" /> </td> Based on the above code, using jQuery, would it be possible that when the page finishes loading, search for the img src "shuttle_last.png" and append to it's onclick call, my own function get_Count(); ? That is, I would then see the following code when I do a view page source for this particular line, i.e.: <img src="/i/mydb/icons/shuttle_last.png" onclick="g_Shuttlep_v61.move_all();get_Count();" alt="Move All" title="Move All"/> Is this possible - if so, would really appreciate a code sample? Thanks.

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• Java Function Analysis

  - by khan

  Okay..I am a total Python guy and have very rarely worked with Java and its methods. The condition is that I have a got a Java function that I have to explain to my instructor and I have got no clue about how to do so..so if one of you can read this properly, kindly help me out in breaking it down and explaining it. Also, i need to find out any flaw in its operation (i.e. usage of loops, etc.) if there is any. Finally, what is the difference between 'string' and 'string[]' types? public static void search(String findfrom, String[] thething){ if(thething.length > 5){ System.err.println("The thing is quite long"); } else{ int[] rescount = new int[thething.length]; for(int i = 0; i < thething.length; i++){ String[] characs = findfrom.split("[ \"\'\t\n\b\f\r]", 0); for(int j = 0; j < characs.length; j++){ if(characs[j].compareTo(thething[i]) == 0){ rescount[i]++; } } } for (int j = 0; j < thething.length; j++) { System.out.println(thething[j] + ": " + rescount[j]); } } }

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• What is the rationale to not allow overloading of C++ conversions operator with non-member function

  - by Vicente Botet Escriba

  C++0x has added explicit conversion operators, but they must always be defined as members of the Source class. The same applies to the assignment operator, it must be defined on the Target class. When the Source and Target classes of the needed conversion are independent of each other, neither the Source can define a conversion operator, neither the Target can define a constructor from a Source. Usually we get it by defining a specific function such as Target ConvertToTarget(Source& v); If C++0x allowed to overload conversion operator by non member functions we could for example define the conversion implicitly or explicitly between unrelated types. template < typename To, typename From > operator To(const From& val); For example we could specialize the conversion from chrono::time_point to posix_time::ptime as follows template < class Clock, class Duration> operator boost::posix_time::ptime( const boost::chrono::time_point<Clock, Duration>& from) { using namespace boost; typedef chrono::time_point<Clock, Duration> time_point_t; typedef chrono::nanoseconds duration_t; typedef duration_t::rep rep_t; rep_t d = chrono::duration_cast<duration_t>( from.time_since_epoch()).count(); rep_t sec = d/1000000000; rep_t nsec = d%1000000000; return posix_time::from_time_t(0)+ posix_time::seconds(static_cast<long>(sec))+ posix_time::nanoseconds(nsec); } And use the conversion as any other conversion. For a more complete description of the problem, see here or on my Boost.Conversion library.. So the question is: What is the rationale to non allow overloading of C++ conversions operator with non-member functions?

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• function working fine in IE but the same funtion is not working for mozilla 3.6

  - by anand-juventus

  function VisibleDiv(obj) { if (obj == BaseLog) { var objStyle = document.getElementById('DivCalls').style; if (objStyle.display == "block") objStyle.display = "none"; else objStyle.display = "block"; } else if (obj == ViewReports) { var objStyle = document.getElementById('DivReports').style; if (objStyle.display == "block") objStyle.display = "none"; else objStyle.display = "block"; } else if (obj ==Management) { var objStyle = document.getElementById('DivManage').style; if (objStyle.display == "block") objStyle.display = "none"; else objStyle.display = "block"; } <a href="#" id="BaseLog" class="TextHeader" onclick="VisibleDiv(this)">Base Log </a> in the above code is working in IE but not working in mozilla 3.6. I have checked that obj==BaseLog is not working in the above code. I have tried many options like event.srcelement window.event.srcelement but all in vain. when I debug the code ,I found that obj is having complete value for IE but the same obj is having all the names .ie. the name of tag,id and class for "Base Log" seperated by #. i.e a#BaseLog#TextHeader# Please suggest what shoud I do?

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• Matlab fft function

  - by CTZStef

  The code below is from the Matlab 2011a help about fft function. I think there is a problem here : why do they multiply t(1:50) by Fs, and then say it's time in millisecond ? Certainly, it happens to be true in this very particular case, but change the value of Fs to, say, 2000, and it won't work anymore, obviously because of this factor of 2. Right ? Quite misleading, isn't it ? What do I miss ? Fs = 1000; % Sampling frequency T = 1/Fs; % Sample time L = 1000; % Length of signal t = (0:L-1)*T; % Time vector % Sum of a 50 Hz sinusoid and a 120 Hz sinusoid x = 0.7*sin(2*pi*50*t) + sin(2*pi*120*t); y = x + 2*randn(size(t)); % Sinusoids plus noise plot(Fs*t(1:50),y(1:50)) title('Signal Corrupted with Zero-Mean Random Noise') xlabel('time (milliseconds)') Clearer with this : fs = 2000; % Sampling frequency T = 1 / fs; % Sample time L = 1000; % Length of signal t2 = (0:L-1)*T; % Time vector f = 50; % signal frequency s2 = sin(2*pi*f*t2); figure, plot(fs*t2(1:50),s2(1:50)); % NOT good figure, plot(t2(1:50),s2(1:50)); % good

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• passing multidimensional arrays to function

  - by Pegah

  hi! I have a method in my class which uses a 3dimensional tfpairexp as input parameter. and I need to use the values in tfpairexp later. void calctfpairexp (int tf1, int tf2, double tfpairexp[][2][3]) { int ctr,c; for (int j = 0; j < cchips && (c = chips[j].crepls); j += c) { int ctrl_no=0; for (int *p = chips[j].ctrl ; p && (ctr=*p)>=0; ++p,ctrl_no++) { for (int k = 0; k < c; ++k) { tfpairexp[j][ctrl_no][k]=interactionFunc(2,3,1); } } } } I call the method inside the class like this: calctfpairexp(tf1,tf2,tfpairexp); and I need to use values inside tfpairexp in next lines. but the compiler gives error in this line: tfpairexp[j][ctrl_no][k]=interactionFunc(2,3,1); and says that the tfpairexp variable is not defined in the calctfpairexp function. any idea?

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• How to access widgets created within functions in later function calls in Qt

  - by Inanepenguin

  So currently I have code, in C++, that creates a few QLabels, a QLineEdit, and a QCheckBox when a selection is made from a QComboBox. However, I would like to be able to access the widgets I have created in a later function to destroy them if a new selection is made from the combo box. I am able to access the objects created from using the Designer by doing ui-Object but i am not able to do that with objects created by using my own code. Can I do that some how, because I know how to work with that. In short, I would like to be able to dynamically create/destroy QWidgets based on selections made by the user. Is there a reference I should know of to do this, or any documentation? Or am I just completely going about this the wrong way? Here is the code I presently have for creating the objects: if (eventType == QString::fromStdString("Birthday")) { QLabel *label1 = new QLabel ("Celebrant: "); QLabel *label2 = new QLabel ("Surprise: "); QLineEdit *lineEdit = new QLineEdit; QCheckBox *box = new QCheckBox; ui->gridLayout->addWidget(label1,3,0,1,1, 0); ui->gridLayout->addWidget(label2,4,0,1,1,0); ui->gridLayout->addWidget(lineEdit,3,1,1,1,0); ui->gridLayout->addWidget(box,4,1,1,2,0); }

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• What's the SQL function for timestamp manipulation?

  - by Eric Leroy

  I'm new to SQL and the time functions are different than mySQL so I'm having a terrible time finding a good site reference with USEFUL timestamp queries. I'm not able to locate the correct way of doing this query in SQL: Id Timestamp ----------------------------------- 1145744 2012-10-10 18:15:11.500 1145743 2012-10-10 18:15:11.313 1145742 2012-10-10 18:15:11.313 1145741 2012-10-10 18:15:11.253 1145740 2012-10-10 18:15:11.190 1145739 2012-10-10 18:15:11.190 1145738 2012-10-10 18:15:11.127 1145737 2012-10-10 18:15:11.067 1145736 2012-10-10 18:15:11.063 1145735 2012-10-10 18:15:10.940 1145734 2012-10-10 18:15:10.817 SELECT * from table WHERE Timestamp ... RANGE I need the range of 2 timestamps so I can select rows by the following parameters: second range minute range hour range day range week range month range year range Is there one function to put in 2 timestamps and get the range? or is this a mix of functions I need? Any good site references would be greatly appriceated. MSDN site isn't helping me isolate the proper way of doing this. I've been searching for about an hour trying to get the last day from 1:30PM to 1:30PM today.

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• struct constructor + function parameter

  - by Oops

  Hi, I am a C++ beginner. I have the following code, the reult is not what I expect. The question is why, resp. what is wrong. For sure, the most of you see it at the first glance. struct Complex { float imag; float real; Complex( float i, float r) { imag = i; real = r; } Complex( float r) { Complex(0, r); } std::string str() { std::ostringstream s; s << "imag: " << imag << " | real: " << real << std::endl; return s.str(); } }; class Complexes { std::vector<Complex> * _complexes; public: Complexes(){ _complexes = new std::vector<Complex>; } void Add( Complex elem ) { _complexes->push_back( elem ); } std::string str( int index ) { std::ostringstream oss; Complex c = _complexes->at(index); oss << c.str(); return oss.str(); } }; int main(){ Complexes * cs = new Complexes(); //cs->Add(123.4f); cs->Add(Complex(123.4f)); std::cout << cs->str(0); return 0; } for now I am interested in the basics of c++ not in the complexnumber theory ;-) it would be nice if the "Add" function does also accept one real (without an extra overloading) instead of only a Complex-object is this possible? many thanks in advance Oops

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• Image Gurus: Optimize my Python PNG transparency function

  - by ozone

  I need to replace all the white(ish) pixels in a PNG image with alpha transparency. I'm using Python in AppEngine and so do not have access to libraries like PIL, imagemagick etc. AppEngine does have an image library, but is pitched mainly at image resizing. I found the excellent little pyPNG module and managed to knock up a little function that does what I need: make_transparent.py pseudo-code for the main loop would be something like: for each pixel: if pixel looks "quite white": set pixel values to transparent otherwise: keep existing pixel values and (assuming 8bit values) "quite white" would be: where each r,g,b value is greater than "240" AND each r,g,b value is within "20" of each other This is the first time I've worked with raw pixel data in this way, and although works, it also performs extremely poorly. It seems like there must be a more efficient way of processing the data without iterating over each pixel in this manner? (Matrices?) I was hoping someone with more experience in dealing with these things might be able to point out some of my more obvious mistakes/improvements in my algorithm. Thanks!

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• Time complexity of a powerset generating function

  - by Lirik

  I'm trying to figure out the time complexity of a function that I wrote (it generates a power set for a given string): public static HashSet<string> GeneratePowerSet(string input) { HashSet<string> powerSet = new HashSet<string>(); if (string.IsNullOrEmpty(input)) return powerSet; int powSetSize = (int)Math.Pow(2.0, (double)input.Length); // Start at 1 to skip the empty string case for (int i = 1; i < powSetSize; i++) { string str = Convert.ToString(i, 2); string pset = str; for (int k = str.Length; k < input.Length; k++) { pset = "0" + pset; } string set = string.Empty; for (int j = 0; j < pset.Length; j++) { if (pset[j] == '1') { set = string.Concat(set, input[j].ToString()); } } powerSet.Add(set); } return powerSet; } So my attempt is this: let the size of the input string be n in the outer for loop, must iterate 2^n times (because the set size is 2^n). in the inner for loop, we must iterate 2*n times (at worst). 1. So Big-O would be O((2^n)*n) (since we drop the constant 2)... is that correct? And n*(2^n) is worse than n^2. if n = 4 then (4*(2^4)) = 64 (4^2) = 16 if n = 100 then (10*(2^10)) = 10240 (10^2) = 100 2. Is there a faster way to generate a power set, or is this about optimal?

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• C++ compiler unable to find function (namespace related)

  - by CS student

  I'm working in Visual Studio 2008 on a C++ programming assignment. We were supplied with files that define the following namespace hierarchy (the names are just for the sake of this post, I know "namespace XYZ-NAMESPACE" is redundant): (MAIN-NAMESPACE){ a bunch of functions/classes I need to implement... (EXCEPTIONS-NAMESPACE){ a bunch of exceptions } (POINTER-COLLECTIONS-NAMESPACE){ Set and LinkedList classes, plus iterators } } The MAIN-NAMESPACE contents are split between a bunch of files, and for some reason which I don't understand the operator<< for both Set and LinkedList is entirely outside of the MAIN-NAMESPACE (but within Set and LinkedList's header file). Here's the Set version: template<typename T> std::ostream& operator<<(std::ostream& os, const MAIN-NAMESPACE::POINTER-COLLECTIONS-NAMESPACE::Set<T>& set) Now here's the problem: I have the following data structure: Set A Set B Set C double num It's defined to be in a class within MAIN-NAMESPACE. When I create an instance of the class, and try to print one of the sets, it tells me that: error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'const MAIN-NAMESPACE::POINTER-COLLECTIONS-NAMESPACE::Set' (or there is no acceptable conversion) However, if I just write a main() function, and create Set A, fill it up, and use the operator- it works. Any idea what is the problem? (note: I tried any combination of using and include I could think of).

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