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  • ask help: I need to create a demo application in Java to test my new designed Java Api

    - by Christophe
    A new programmer needs yourhelp. I'm working on a porject of re-developement of Java driver for the company's PIN pad terminals. the Java Api (CPXApplicationUpdate) will allow the applications in pinpads to be updated and to be downloaded at different speed (Baud rate). the Java Api was created. i followed the protocolto build the message. the message is to send to a RS-232 port. i'm trying to use setter and getter to let the code work as an API. import java.io.InputStream; import java.io.OutputStream; import java.util.Properties; public class CPXApplicationUpdate extends CPXCommand { private int speed; // TODO: temporary variable for baud rate test stub. // speed: baud rate of the maintenance application performing DL /** Creates a new instance of CPXApplicationUpdate */ public CPXApplicationUpdate() { speed = 9600; // no baud rate change CPXProcessor.logger.fine("-------CPXApplicationUpdate constructor"); // setParam("timeout", _cmdInfo.getDefaultParValue("timeout")); } public CPXApplicationUpdate(int speedinit) { speed = speedinit; // TODO: where to get the speed? wait for user input. CPXProcessor.logger.fine("-------CPXApplicationUpdate constructor"); // setParam("timeout", _cmdInfo.getDefaultParValue("timeout")); } public void setSpeed(int speed){ this.speed = speed; } protected void buildRequest() throws ElitePortException { String trans = ""; // build the full-qualified message trans = addToRequest(trans, (char) 0); trans = addToRequest(trans, (char) 5); trans = addToRequest(trans, (char) 6); trans = addToRequest(trans, (char) 0); trans = addToRequest(trans, (char) 0); trans = addToRequest(trans, (char) 2); switch (speed) { case 9600: trans = addToRequest(trans, (char) 0x09); break; case 19200: trans = addToRequest(trans, (char) 0x0A); break; case 115200: trans = addToRequest(trans, (char) 0x0E); break; default: // TODO: unexpected baud rate. throw(); break; } trans = EncryptBinary(trans); trans = "F0." + trans; wrapRequest(trans); } protected String addToRequest(String req, char c) { CPXProcessor.logger.fine("adding char to request: I-" + (int) c + " C-" + c + " H-" + Integer.toHexString((int) c)); return req + c; } protected String addToRequest(String req, String s) { CPXProcessor.logger.fine("adding String to request: S-" + s); return req + s; } protected String addToRequest(String req) { return req; } public void analyzeResponse() { String response_transaction, response; int absLen = _response.length(); if (absLen < 4) return; response = _response.substring(3); CPXProcessor.logger.fine("stripped response=[" + response + "]"); for (int i = 0; i < response.length(); i++) { char c = response.charAt(i); CPXProcessor.logger.fine("[" + i + "] = " + c + " <> " + Integer.toHexString((int) c)); } int status = (short) response.charAt(3); CPXProcessor.logger.fine("status = " + status); _outputValues.put("status", "" + status); } please help me to correct the code. Now, i need to create a demo application to test if this java driver (Java Api) works. the value of the speed can be input by users (command line), or creat property files. how can i do that?

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  • How to find the number of inversions in an array ?

    - by Michael
    This is an phone interview question: "Find the number of inversions in an array". I guess they mean O(N*log N) solution since O(N^2) is trivial. I guess it cannot be better than O(N*log N) since sorting is O(N*log N) I have checked a similar question from SO and can summarize the answers as follows: Calculate half the distance the elements should be moved to sort the array : copy the array and sort the copy. For each element of the original array a[i] find it's position j in the sorted copy (binary search) and sum abs(i - j)/2. Modify merge sort : modify merge to count inversions between two sorted arrays (it takes O(N)) and run merge sort with the modified merge. Does it make sense ? Are there other (maybe simpler) solution ? Isn't it too hard for a phone interview ?

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  • Why does JavaScript's getElementsByClassName provide an object that is NOT an array?

    - by Paragon
    I'm trying to get a list in JavaScript (not using jQuery) of all the elements on the page with a specific class name. I therefore employ the getElementsByClassName() function as follows: var expand_buttons = document.getElementsByClassName('expand'); console.log(expand_buttons, expand_buttons.length, expand_buttons[0]); Note that I have three anchor elements on my page with the class 'expand'. This console.log() outputs [] 0 undefined Next, for kicks, I threw expand_buttons into its own array as follows: var newArray = new Array(expand_buttons); console.log(newArray, newArray.length); This suddenly outputs [NodeList[3]] 1 and I can click through the nodelist and see the attributes of the three 'expand' anchor elements on the page. It's also worth noting that I was able to get my code working in a w3schools test page. It may also be of note that my use of document.getElementsByName actually does output (to the console) an array of elements, but when I ask for its length, it tells me 0. Similarly, if I try to access an array element using array_name[0] as normal, it outputs 'undefined', despite there clearly being an element inside of an array when I print the object to the console. Does anybody have any idea why this might be? I just want to loop through DOM elements, and I'm avoiding jQuery at the moment because I'm trying to practice coding with vanilla JavaScript. Thanks, ParagonRG

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  • function to org-sort by three (3) criteria: due date / priority / title

    - by lawlist
    Is anyone aware of an org-sort function / modification that can refile / organize a group of TODO so that it sorts them by three (3) criteria: first sort by due date, second sort by priority, and third sort by by title of the task? EDIT: If anyone can please help me to modify this so that undated TODO are sorted last, that would be greatly appreciated -- at the present time, undated TODO are not being sorted: ;; multiple sort (defun org-sort-multi (&rest sort-types) "Multiple sorts on a certain level of an outline tree, or plain list items. SORT-TYPES is a list where each entry is either a character or a cons pair (BOOL . CHAR), where BOOL is whether or not to sort case-sensitively, and CHAR is one of the characters defined in `org-sort-entries-or-items'. Entries are applied in back to front order. Example: To sort first by TODO status, then by priority, then by date, then alphabetically (case-sensitive) use the following call: (org-sort-multi '(?d ?p ?t (t . ?a)))" (interactive) (dolist (x (nreverse sort-types)) (when (char-valid-p x) (setq x (cons nil x))) (condition-case nil (org-sort-entries (car x) (cdr x)) (error nil)))) ;; sort current level (defun lawlist-sort (&rest sort-types) "Sort the current org level. SORT-TYPES is a list where each entry is either a character or a cons pair (BOOL . CHAR), where BOOL is whether or not to sort case-sensitively, and CHAR is one of the characters defined in `org-sort-entries-or-items'. Entries are applied in back to front order. Defaults to \"?o ?p\" which is sorted by TODO status, then by priority" (interactive) (when (equal mode-name "Org") (let ((sort-types (or sort-types (if (or (org-entry-get nil "TODO") (org-entry-get nil "PRIORITY")) '(?d ?t ?p) ;; date, time, priority '((nil . ?a)))))) (save-excursion (outline-up-heading 1) (let ((start (point)) end) (while (and (not (bobp)) (not (eobp)) (<= (point) start)) (condition-case nil (outline-forward-same-level 1) (error (outline-up-heading 1)))) (unless (> (point) start) (goto-char (point-max))) (setq end (point)) (goto-char start) (apply 'org-sort-multi sort-types) (goto-char end) (when (eobp) (forward-line -1)) (when (looking-at "^\\s-*$") ;; (delete-line) ) (goto-char start) ;; (dotimes (x ) (org-cycle)) )))))

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  • Is there any way to pass an anonymous array as an argument in C++?

    - by Jeremy Friesner
    Hi all, I'd like to be able to declare an array as a function argument in C++, as shown in the example code below (which doesn't compile). Is there any way to do this (other than declaring the array separately beforehand)? #include <stdio.h> static void PrintArray(int arrayLen, const int * array) { for (int i=0; i<arrayLen; i++) printf("%i -> %i\n", i, array[i]); } int main(int, char **) { PrintArray(5, {5,6,7,8,9} ); // doesn't compile return 0; }

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  • How detect length of a numpy array with only one element?

    - by mishaF
    I am reading in a file using numpy.genfromtxt which brings in columns of both strings and numeric values. One thing I need to do is detect the length of the input. This is all fine provided there are more than one value read into each array. But...if there is only one element in the resulting array, the logic fails. I can recreate an example here: import numpy as np a = np.array(2.3) len(a) returns an error saying: TypeError: len() of unsized object however, If a has 2 or more elements, len() behaves as one would expect. import numpy as np a = np.array([2.3,3.6]) len(a) returns 2 My concern here is, if I use some strange exception handling, I can't distinguish between a being empty and a having length = 1.

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  • how to represent negative number to array of integers ?

    - by stdnoit
    I must convert string of 1324312321 to array of integers in java this is fine. I could use integer parseint and string substring method but how do I repesent -12312312 to my original array of integer.. the fact that - is a char / string and convert to array of integer would alter the value ( even though I convert - to integer-equivalent , it would change the rest of 12312312) it must be an array of integers and how should I convert negative numbers and still keeep the same value somehow reminding me of two complements trick but i dont think i need to go down to binary level in my program.. any other trick for doing this? thanks!

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  • C++ Filling an 1D array to represent a n-dimensional object based on a straight line segment

    - by Ben
    I'm struggling to find a good way to put this question but here goes. I'm making a system that uses a 1D array implemented as double * parts_ = new double[some_variable];. I want to use this to hold co-ordinates for a particle system that can run in various dimensions. What I want to be able to do is write a generic fill algorithm for filling this in n-dimensions with a common increment in all direction to a variable size. Examples will serve best I think. Consider the case where the number of particles stored by the array is 4 In 1D this produces 4 elements in the array because each particle only has one co-ordinate. 1D: {0, 25, 50, 75}; In 2D this produces 8 elements in the array because each particle has two co-ordinates.. 2D: {0, 0, 0, 25, 25, 0, 25, 25} In 3D this produces 12 elements in the array because each particle now has three co-ordinates {0, 0, 0, 0, 0, 25, 0, 0, 50, ... } These examples are still not quite accurate, but they hopefully will suffice. The way I would do this normally for two dimensions: int i = 0; for(int x = 0; x < parts_size_ / dims_ / dims_ * 25; x += 25) { for(int y = 0; y < parts_size_ / dims_ / dims_ * 25; y += 25) { parts_[i] = x; parts_[i+1] = y; i+=2; // Indentation hates me today .< How can I implement this for n-dimensions where 25 can be any number? The straight line part is because it seems to me logical that a line is a somewhat regular shape in 1D, as is a square in 2D, and a cube in 3D. It seems to me that it would follow that there would be similar shapes in this family that could be implemented for 4D and higher dimensions via a similar fill pattern. This is the shape I wish to set my array to represent.

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  • Given an array of arguments, how do I send those arguments to a particular function in Ruby?

    - by Steven Xu
    Forgive the beginner question, but say I have an array: a = [1,2,3] And a function somewhere; let's say it's an instance function: class Ilike def turtles(*args) puts args.inspect end end How do I invoke Ilike.turtles with a as if I were calling (Ilike.new).turtles(1,2,3). I'm familiar with send, but this doesn't seem to translate an array into an argument list. A parallel of what I'm looking for is the Javascript apply, which is equivalent to call but converts the array into an argument list.

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  • How can I pass an array resulting from a Perl method by reference?

    - by arareko
    Some XML::LibXML methods return arrays instead of references to arrays. Instead of doing this: $self->process_items($xml->findnodes('items/item')); I want to do something like: $self->process_items(\$xml->findnodes('items/item')); So that in process_items() I can dereference the original array instead of creating a copy: sub process_items { my ($self, $items) = @_; foreach my $item (@$items) { # do something... } } I can always store the results of findnodes() into an array and then pass the array reference to my own method, but let's say I want to try a reduced version of my code. Is that the correct syntax for passing the method results or should I use something different? Thanks! EDIT: Now suppose I want to change process_items() to process_item() so I can do stuff on a single element of the referenced array inside a loop. Something like: $self->process_item($_) for ([ $xml->findnodes('items/item') ]); This doesn't work as process_item() is executed only once because a single value is passed to the for loop (the reference to the array from findnodes()). What's the proper way of using $_ in this case?

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  • JavaScript: Is there a better way to retain your array but efficiently concat or replace items?

    - by Michael Mikowski
    I am looking for the best way to replace or add to elements of an array without deleting the original reference. Here is the set up: var a = [], b = [], c, i, obj; for ( i = 0; i < 100000; i++ ) { a[ i ] = i; b[ i ] = 10000 - i; } obj.data_list = a; Now we want to concatenate b INTO a without changing the reference to a, since it is used in obj.data_list. Here is one method: for ( i = 0; i < b.length; i++ ) { a.push( b[ i ] ); } This seems to be a somewhat terser and 8x (on V8) faster method: a.splice.apply( a, [ a.length, 0 ].concat( b ) ); I have found this useful when iterating over an "in-place" array and don't want to touch the elements as I go (a good practice). I start a new array (let's call it keep_list) with the initial arguments and then add the elements I wish to retain. Finally I use this apply method to quickly replace the truncated array: var keep_list = [ 0, 0 ]; for ( i = 0; i < a.length; i++ ){ if ( some_condition ){ keep_list.push( a[ i ] ); } // truncate array a.length = 0; // And replace contents a.splice.apply( a, keep_list ); There are a few problems with this solution: there is a max call stack size limit of around 50k on V8 I have not tested on other JS engines yet. This solution is a bit cryptic Has anyone found a better way?

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  • Which of these Array Initializations is better in Ruby?

    - by Bragaadeesh
    Hi, Which of these two forms of Array Initialization is better in Ruby? Method 1: DAYS_IN_A_WEEK = (0..6).to_a HOURS_IN_A_DAY = (0..23).to_a @data = Array.new(DAYS_IN_A_WEEK.size).map!{ Array.new(HOURS_IN_A_DAY.size) } DAYS_IN_A_WEEK.each do |day| HOURS_IN_A_DAY.each do |hour| @data[day][hour] = 'something' end end Method 2: DAYS_IN_A_WEEK = (0..6).to_a HOURS_IN_A_DAY = (0..23).to_a @data = {} DAYS_IN_A_WEEK.each do |day| HOURS_IN_A_DAY.each do |hour| @data[day] ||= {} @data[day][hour] = 'something' end end The difference between the first method and the second method is that the second one does not allocate memory initially. I feel the second one is a bit inferior when it comes to performance due to the numerous amount of Array copies that has to happen. However, it is not straight forward in Ruby to find what is happening. So, if someone can explain me which is better, it would be really great! Thanks

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  • What's the best way to have functions share an array in Objective-C?

    - by editor
    I understand that in Objective-C you declare an array in the header file and interact with it in a class. So far I'm adding things and fetching them fine within a single function. I'm new to the language however and can't figure out how to share that array across other functions. I'd like to initialize array data in my viewDidLoad and access it from various functions later on. Is this possible and if so what's the best way to do it?

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  • php: possible to convert array of numbers to 'from' and 'to' pairs where consecutive?

    - by Haroldo
    I have an array of timestamps referring to the days when a holiday home is booked. each timestamp is a round day. I want to turn this into an array of 'begins' and 'ends' pairs for consecutive dates Are there any php functions I should be aware of for writing this function? Or does anyone have any pointers for this kind of thing? thanks! edit: example array: Array ( [0] => 1273536000 [1] => 1273622400 [2] => 1273708800 [3] => 1273795200 [4] => 1273881600 [5] => 1273968000 [6] => 1274054400 [7] => 1274140800 [8] => 1274227200 ) where a day = 86400 (seconds)

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  • JavaScript: String Concatenation slow performance? Array.join('')?

    - by NickNick
    I've read that if I have a for loop, I should not use string concation because it's slow. Such as: for (i=0;i<10000000;i++) { str += 'a'; } And instead, I should use Array.join(), since it's much faster: var tmp = []; for (i=0;i<10000000;i++) { tmp.push('a'); } var str = tmp.join(''); However, I have also read that string concatention is ONLY a problem for Internet Explorer and that browsers such as Safari/Chrome, which use Webkit, actually perform FASTER is using string concatention than Array.join(). I've attempting to find a performance comparison between all major browser of string concatenation vs Array.join() and haven't been able to find one. As such, what is faster and more efficient JavaScript code? Using string concatenation or Array.join()?

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  • Grading an algorithm: Readability vs. Compactness

    - by amiregelz
    Consider the following question in a test \ interview: Implement the strcpy() function in C: void strcpy(char *destination, char *source); The strcpy function copies the C string pointed by source into the array pointed by destination, including the terminating null character. Assume that the size of the array pointed by destination is long enough to contain the same C string as source, and does not overlap in memory with source. Say you were the tester, how would you grade the following answers to this question? 1) void strcpy(char *destination, char *source) { while (*source != '\0') { *destination = *source; source++; destionation++; } *destionation = *source; } 2) void strcpy(char *destination, char *source) { while (*(destination++) = *(source++)) ; } The first implementation is straightforward - it is readable and programmer-friendly. The second implementation is shorter (one line of code) but less programmer-friendly; it's not so easy to understand the way this code is working, and if you're not familiar with the priorities in this code then it's a problem. I'm wondering if the first answer would show more complexity and more advanced thinking, in the tester's eyes, even though both algorithms behave the same, and although code readability is considered to be more important than code compactness. It seems to me that since making an algorithm this compact is more difficult to implement, it will show a higher level of thinking as an answer in a test. However, it is also possible that a tester would consider the first answer not good because it's not readable. I would also like to mention that this is not specific to this example, but general for code readability vs. compactness when implementing an algorithm, specifically in tests \ interviews.

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  • Windows recv method usage

    - by vandamon taigi
    I'm making a multiplayer game and I have an issue with the recv function ( or the send one , not sure ). Server side code : char* UserName = new char[256]; ZeroMemory(UserName,256); recv(sConnect,UserName,256,0); // works char* Password = new char[256]; ZeroMemory(Password,256); recv(sConnect,Password,256,0); // works users[ ++usercount ] = new Client(UserName,Password,sConnect); if( users[usercount] ->GetLogInSuccesful() ) send(sConnect,"0x0001",6,0); // debugging shows it gets here and sends the data. Client side code : send(server->getsConnect(),User,256,0); // works send(server->getsConnect(),Pass,256,0); // works char* Response = new char[6]; ZeroMemory(Response,6); recv(server->getsConnect(),Response,6,0); // gets stuck here. Any ideea why does it get stuck on that recv ? I also tried by making response [256] or such.

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  • How should I group these variables?

    - by stariz77
    I have a shape that will be defined by: char s_type; char color; double height; double width; These variables are scanned in from a request string sent to my server and passed into my printing function, which then prints out the shape. Currently they are just local variables sitting in my main(); however, I was wondering if there would be any advantage in creating a struct containing these variables, and then passing the struct to my printing function? or how else might I improve my program's structure/style, would passing a struct by reference have any kind of performance benefit if there were many requests and therefore many printing function calls? printer(char st, char cr, double ht, double wd); int main() { // Other main functionality. char s_type; char color; double height; double width; sscanf (serv_req, "GET /%c/%c/%lf/%lf", &s_type, &color, &height, &width); printer(s_type, color, height, width); // Other main functionality. return 0; } It seemed "neater" if I had a struct or something that didn't leave me with declarations in the middle of everything else going on in main. I'm interested in structure/style as well as performance. EDIT: didn't mean to put printer declaration inside main.

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  • Drupal: Create custom search

    - by Dr. Hfuhruhurr
    I'm trying to create a custom search but getting stuck. What I want is to have a dropdownbox so the user can choose where to search in. These options can mean 1 or more content types. So if he chooses options A, then the search will look in node-type P,Q,R. But he may not give those results, but only the uid's which will be then themed to gather specific data for that user. To make it a little bit clearer, Suppose I want to llok for people. The what I'm searching in is 2 content profile types. But ofcourse you dont want to display those as a result, but a nice picture of the user and some data. I started with creating a form with a textfield and the dropdown box. Then, in the submit handler, i created the keys and redirected to another pages with those keys as a tail. This page has been defined in the menu hook, just like how search does it. After that I want to call hook_view to do the actual search by calling node_search, and give back the results. Unfortunately, it goes wrong. When i click the Search button, it gives me a 404. But am I on the right track? Is this the way to create a custom search? Thx for your help. Here's the code for some clarity: <?php // $Id$ /* * @file * Searches on Project, Person, Portfolio or Group. */ /** * returns an array of menu items * @return array of menu items */ function vm_search_menu() { $subjects = _vm_search_get_subjects(); foreach ($subjects as $name => $description) { $items['zoek/'. $name .'/%menu_tail'] = array( 'page callback' => 'vm_search_view', 'page arguments' => array($name), 'type' => MENU_LOCAL_TASK, ); } return $items; } /** * create a block to put the form into. * @param $op * @param $delta * @param $edit * @return mixed */ function vm_search_block($op = 'list', $delta = 0, $edit = array()) { switch ($op) { case 'list': $blocks[0]['info'] = t('Algemene zoek'); return $blocks; case 'view': if (0 == $delta) { $block['subject'] = t(''); $block['content'] = drupal_get_form('vm_search_general_form'); } return $block; } } /** * Define the form. */ function vm_search_general_form() { $subjects = _vm_search_get_subjects(); foreach ($subjects as $key => $subject) { $options[$key] = $subject['desc']; } $form['subjects'] = array( '#type' => 'select', '#options' => $options, '#required' => TRUE, ); $form['keys'] = array( '#type' => 'textfield', '#required' => TRUE, ); $form['submit'] = array( '#type' => 'submit', '#value' => t('Zoek'), ); return $form; } function vm_search_general_form_submit($form, &$form_state) { $subjects = _vm_search_get_subjects(); $keys = $form_state['values']['keys']; //the search keys //the content types to search in $keys .= ' type:' . implode(',', $subjects[$form_state['values']['subjects']]['types']); //redirect to the page, where vm_search_view will handle the actual search $form_state['redirect'] = 'zoek/'. $form_state['values']['subjects'] .'/'. $keys; } /** * Menu callback; presents the search results. */ function vm_search_view($type = 'node') { // Search form submits with POST but redirects to GET. This way we can keep // the search query URL clean as a whistle: // search/type/keyword+keyword if (!isset($_POST['form_id'])) { if ($type == '') { // Note: search/node can not be a default tab because it would take on the // path of its parent (search). It would prevent remembering keywords when // switching tabs. This is why we drupal_goto to it from the parent instead. drupal_goto($front_page); } $keys = search_get_keys(); // Only perform search if there is non-whitespace search term: $results = ''; if (trim($keys)) { // Log the search keys: watchdog('vm_search', '%keys (@type).', array('%keys' => $keys, '@type' => $type)); // Collect the search results: $results = node_search('search', $type); if ($results) { $results = theme('box', t('Zoek resultaten'), $results); } else { $results = theme('box', t('Je zoek heeft geen resultaten opgeleverd.')); } } } return $results; } /** * returns array where to look for * @return array */ function _vm_search_get_subjects() { $subjects['opdracht'] = array('desc' => t('Opdracht'), 'types' => array('project') ); $subjects['persoon'] = array('desc' => t('Persoon'), 'types' => array('types_specialisatie', 'smaak_en_interesses') ); $subjects['groep'] = array('desc' => t('Groep'), 'types' => array('Villamedia_groep') ); $subjects['portfolio'] = array('desc' => t('Portfolio'), 'types' => array('artikel') ); return $subjects; }

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  • Possible to migrate from non-RAID to RAID 1 and then RAID 5?

    - by stueng
    Using software RAID only Is it possible to start with a 2TB disk full of data and safely add it to a RAID 1 array? Is it then possible to add a third disk and migrate the RAID 1 array into a RAID 5 array? OR Is it possible to start with a 2 disk degraded RAID 5 array and then add the third disk later to create a health RAID 5 array? Backstory: I wish to migrate from a 2 disk NAS (RAID 1) to a 3 disk NAS and only purchase one new disk in doing so

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  • undefined reference to function, despite giving reference in c

    - by Jamie Edwards
    I'm following a tutorial, but when it comes to compiling and linking the code I get the following error: /tmp/cc8gRrVZ.o: In function `main': main.c:(.text+0xa): undefined reference to `monitor_clear' main.c:(.text+0x16): undefined reference to `monitor_write' collect2: ld returned 1 exit status make: *** [obj/main.o] Error 1 What that is telling me is that I haven't defined both 'monitor_clear' and 'monitor_write'. But I have, in both the header and source files. They are as follows: monitor.c: // monitor.c -- Defines functions for writing to the monitor. // heavily based on Bran's kernel development tutorials, // but rewritten for JamesM's kernel tutorials. #include "monitor.h" // The VGA framebuffer starts at 0xB8000. u16int *video_memory = (u16int *)0xB8000; // Stores the cursor position. u8int cursor_x = 0; u8int cursor_y = 0; // Updates the hardware cursor. static void move_cursor() { // The screen is 80 characters wide... u16int cursorLocation = cursor_y * 80 + cursor_x; outb(0x3D4, 14); // Tell the VGA board we are setting the high cursor byte. outb(0x3D5, cursorLocation >> 8); // Send the high cursor byte. outb(0x3D4, 15); // Tell the VGA board we are setting the low cursor byte. outb(0x3D5, cursorLocation); // Send the low cursor byte. } // Scrolls the text on the screen up by one line. static void scroll() { // Get a space character with the default colour attributes. u8int attributeByte = (0 /*black*/ << 4) | (15 /*white*/ & 0x0F); u16int blank = 0x20 /* space */ | (attributeByte << 8); // Row 25 is the end, this means we need to scroll up if(cursor_y >= 25) { // Move the current text chunk that makes up the screen // back in the buffer by a line int i; for (i = 0*80; i < 24*80; i++) { video_memory[i] = video_memory[i+80]; } // The last line should now be blank. Do this by writing // 80 spaces to it. for (i = 24*80; i < 25*80; i++) { video_memory[i] = blank; } // The cursor should now be on the last line. cursor_y = 24; } } // Writes a single character out to the screen. void monitor_put(char c) { // The background colour is black (0), the foreground is white (15). u8int backColour = 0; u8int foreColour = 15; // The attribute byte is made up of two nibbles - the lower being the // foreground colour, and the upper the background colour. u8int attributeByte = (backColour << 4) | (foreColour & 0x0F); // The attribute byte is the top 8 bits of the word we have to send to the // VGA board. u16int attribute = attributeByte << 8; u16int *location; // Handle a backspace, by moving the cursor back one space if (c == 0x08 && cursor_x) { cursor_x--; } // Handle a tab by increasing the cursor's X, but only to a point // where it is divisible by 8. else if (c == 0x09) { cursor_x = (cursor_x+8) & ~(8-1); } // Handle carriage return else if (c == '\r') { cursor_x = 0; } // Handle newline by moving cursor back to left and increasing the row else if (c == '\n') { cursor_x = 0; cursor_y++; } // Handle any other printable character. else if(c >= ' ') { location = video_memory + (cursor_y*80 + cursor_x); *location = c | attribute; cursor_x++; } // Check if we need to insert a new line because we have reached the end // of the screen. if (cursor_x >= 80) { cursor_x = 0; cursor_y ++; } // Scroll the screen if needed. scroll(); // Move the hardware cursor. move_cursor(); } // Clears the screen, by copying lots of spaces to the framebuffer. void monitor_clear() { // Make an attribute byte for the default colours u8int attributeByte = (0 /*black*/ << 4) | (15 /*white*/ & 0x0F); u16int blank = 0x20 /* space */ | (attributeByte << 8); int i; for (i = 0; i < 80*25; i++) { video_memory[i] = blank; } // Move the hardware cursor back to the start. cursor_x = 0; cursor_y = 0; move_cursor(); } // Outputs a null-terminated ASCII string to the monitor. void monitor_write(char *c) { int i = 0; while (c[i]) { monitor_put(c[i++]); } } void monitor_write_hex(u32int n) { s32int tmp; monitor_write("0x"); char noZeroes = 1; int i; for (i = 28; i > 0; i -= 4) { tmp = (n >> i) & 0xF; if (tmp == 0 && noZeroes != 0) { continue; } if (tmp >= 0xA) { noZeroes = 0; monitor_put (tmp-0xA+'a' ); } else { noZeroes = 0; monitor_put( tmp+'0' ); } } tmp = n & 0xF; if (tmp >= 0xA) { monitor_put (tmp-0xA+'a'); } else { monitor_put (tmp+'0'); } } void monitor_write_dec(u32int n) { if (n == 0) { monitor_put('0'); return; } s32int acc = n; char c[32]; int i = 0; while (acc > 0) { c[i] = '0' + acc%10; acc /= 10; i++; } c[i] = 0; char c2[32]; c2[i--] = 0; int j = 0; while(i >= 0) { c2[i--] = c[j++]; } monitor_write(c2); } monitor.h: // monitor.h -- Defines the interface for monitor.h // From JamesM's kernel development tutorials. #ifndef MONITOR_H #define MONITOR_H #include "common.h" // Write a single character out to the screen. void monitor_put(char c); // Clear the screen to all black. void monitor_clear(); // Output a null-terminated ASCII string to the monitor. void monitor_write(char *c); #endif // MONITOR_H common.c: // common.c -- Defines some global functions. // From JamesM's kernel development tutorials. #include "common.h" // Write a byte out to the specified port. void outb ( u16int port, u8int value ) { asm volatile ( "outb %1, %0" : : "dN" ( port ), "a" ( value ) ); } u8int inb ( u16int port ) { u8int ret; asm volatile ( "inb %1, %0" : "=a" ( ret ) : "dN" ( port ) ); return ret; } u16int inw ( u16int port ) { u16int ret; asm volatile ( "inw %1, %0" : "=a" ( ret ) : "dN" ( port ) ); return ret; } // Copy len bytes from src to dest. void memcpy(u8int *dest, const u8int *src, u32int len) { const u8int *sp = ( const u8int * ) src; u8int *dp = ( u8int * ) dest; for ( ; len != 0; len-- ) *dp++ =*sp++; } // Write len copies of val into dest. void memset(u8int *dest, u8int val, u32int len) { u8int *temp = ( u8int * ) dest; for ( ; len != 0; len-- ) *temp++ = val; } // Compare two strings. Should return -1 if // str1 < str2, 0 if they are equal or 1 otherwise. int strcmp(char *str1, char *str2) { int i = 0; int failed = 0; while ( str1[i] != '\0' && str2[i] != '\0' ) { if ( str1[i] != str2[i] ) { failed = 1; break; } i++; } // Why did the loop exit? if ( ( str1[i] == '\0' && str2[i] != '\0' || (str1[i] != '\0' && str2[i] =='\0' ) ) failed =1; return failed; } // Copy the NULL-terminated string src into dest, and // return dest. char *strcpy(char *dest, const char *src) { do { *dest++ = *src++; } while ( *src != 0 ); } // Concatenate the NULL-terminated string src onto // the end of dest, and return dest. char *strcat(char *dest, const char *src) { while ( *dest != 0 ) { *dest = *dest++; } do { *dest++ = *src++; } while ( *src != 0 ); return dest; } common.h: // common.h -- Defines typedefs and some global functions. // From JamesM's kernel development tutorials. #ifndef COMMON_H #define COMMON_H // Some nice typedefs, to standardise sizes across platforms. // These typedefs are written for 32-bit x86. typedef unsigned int u32int; typedef int s32int; typedef unsigned short u16int; typedef short s16int; typedef unsigned char u8int; typedef char s8int; void outb ( u16int port, u8int value ); u8int inb ( u16int port ); u16int inw ( u16int port ); #endif //COMMON_H main.c: // main.c -- Defines the C-code kernel entry point, calls initialisation routines. // Made for JamesM's tutorials <www.jamesmolloy.co.uk> #include "monitor.h" int main(struct multiboot *mboot_ptr) { monitor_clear(); monitor_write ( "hello, world!" ); return 0; } here is my makefile: C_SOURCES= main.c monitor.c common.c S_SOURCES= boot.s C_OBJECTS=$(patsubst %.c, obj/%.o, $(C_SOURCES)) S_OBJECTS=$(patsubst %.s, obj/%.o, $(S_SOURCES)) CFLAGS=-nostdlib -nostdinc -fno-builtin -fno-stack-protector -m32 -Iheaders LDFLAGS=-Tlink.ld -melf_i386 --oformat=elf32-i386 ASFLAGS=-felf all: kern/kernel .PHONY: clean clean: -rm -f kern/kernel kern/kernel: $(S_OBJECTS) $(C_OBJECTS) ld $(LDFLAGS) -o $@ $^ $(C_OBJECTS): obj/%.o : %.c gcc $(CFLAGS) $< -o $@ vpath %.c source $(S_OBJECTS): obj/%.o : %.s nasm $(ASFLAGS) $< -o $@ vpath %.s asem Hopefully this will help you understand what is going wrong and how to fix it :L Thanks in advance. Jamie.

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