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• I am getting null pointer exception while publishing dynamic web project on jboss using eclipse

  - by Rozer

  I am getting null pointer exception while publishing dynamic web project on jboss using eclipse Environment details Version: 3.3.2 Build id: M20080221-1800 Jboss: 3.2.3 JDK 1.5 I have checked with google, but nothing work, can anyone suggest me what is the root cause for that Following is the log trace may be help to understance the situation !ENTRY org.eclipse.wst.server.core 4 0 2010-06-13 19:03:44.568 !MESSAGE Error calling delegate restart() JBOSS 4.0 !ENTRY org.eclipse.wst.server.core 4 0 2010-06-13 19:39:34.365 !MESSAGE Could not publish to the server. !STACK 0 java.lang.NullPointerException at org.eclipse.wst.common.componentcore.internal.util.ComponentUtilities.getDeployUriOfComponent(ComponentUtilities.java:327) at org.eclipse.jst.j2ee.internal.deployables.J2EEFlexProjDeployable.getURI(J2EEFlexProjDeployable.java:429) at org.eclipse.jst.server.generic.core.internal.publishers.AntPublisher.guessModuleName(AntPublisher.java:259) at org.eclipse.jst.server.generic.core.internal.publishers.AntPublisher.getPublishProperties(AntPublisher.java:224) at org.eclipse.jst.server.generic.core.internal.publishers.AntPublisher.publish(AntPublisher.java:110) at org.eclipse.jst.server.generic.core.internal.GenericServerBehaviour.publishModule(GenericServerBehaviour.java:84) at org.eclipse.wst.server.core.model.ServerBehaviourDelegate.publishModule(ServerBehaviourDelegate.java:749) at org.eclipse.wst.server.core.model.ServerBehaviourDelegate.publishModules(ServerBehaviourDelegate.java:835) at org.eclipse.wst.server.core.model.ServerBehaviourDelegate.publish(ServerBehaviourDelegate.java:669) at org.eclipse.wst.server.core.internal.Server.doPublish(Server.java:887) at org.eclipse.wst.server.core.internal.Server.publish(Server.java:874) at org.eclipse.wst.server.core.internal.PublishServerJob.run(PublishServerJob.java:72) at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)

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• boost bind callback function pointer as a parameter

  - by Takashi-kun

  I am trying to pass a function pointer using boost::bind. void Class::ThreadFunction(Type(*callbackFunc)(message_type::ptr&)) { } boost::shared_ptr<boost::thread> Class::Init(Type(*callbackFunc)(message_type::ptr&)) { return boost::shared_ptr<boost::thread> ( new boost::thread(boost::bind(&Class::ThreadFunction, callbackFunc)) ); } I get the following errors: 1>C:\dev\sapphire\boost_1_46_1\boost/bind/mem_fn.hpp(362) : warning C4180: qualifier applied to function type has no meaning; ignored 1>C:\dev\sapphire\boost_1_46_1\boost/bind/mem_fn.hpp(333) : error C2296: '->*' : illegal, left operand has type 'Type (__cdecl **)(message_type::ptr &)' However, I was able to change to the following, it works fine: void ThreadFunction(Type(*callbackFunc)(message_type::ptr&)) { } boost::shared_ptr<boost::thread> Class::Init(Type(*callbackFunc)(message_type::ptr&)) { return boost::shared_ptr<boost::thread> ( new boost::thread(boost::bind(&ThreadFunction, callbackFunc)) ); } Why do I get those errors if I declare the method in the Class class?

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• how to set UISwitch pointer to access switch from one uiviewcontroller another uiviewcontroller

  - by Rkm

  System UIViewcontroller has button event.Tap on Button fire InfoTableviewController. InfoTableview has UISwitch . How to set NSMutableArray of UIswitch pointer for System UIViewcontroller to access switch . SystemUIviewcontroller button event - (IBAction) Info_Button_Clicked:(id) sender { // pushcontroller Info *info = [[Info alloc]initWithNibName:@"Info" bundle:[NSBundle mainBundle]]; [self.navigationController pushViewController:info animated:YES]; [info release]; } Here for Info TableviewController // Customize the appearance of table view cells. - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell = nil; if ([indexPath section] == 0) { static NSString *kDisplayCell_ID = @"DisplayCellID"; cell = [self.tableView dequeueReusableCellWithIdentifier: kDisplayCell_ID]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier: kDisplayCell_ID] autorelease]; cell.selectionStyle = UITableViewCellSelectionStyleNone; } else { // the cell is being recycled, remove old embedded controls UIView *viewToRemove = nil; viewToRemove = [cell.contentView viewWithTag:1]; if (viewToRemove) [viewToRemove removeFromSuperview]; } cell.textLabel.text = [[self.Soundarray objectAtIndex: indexPath.row] valueForKey:@"labelKey"]; UIControl *control = [[self.Soundarray objectAtIndex: indexPath.row] valueForKey:@"viewKey"]; [cell.contentView addSubview:control]; return cell; } }

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• Query doesn't use a covering-index when applicable

  - by Dor

  I've downloaded the employees database and executed some queries for benchmarking purposes. Then I noticed that one query didn't use a covering index, although there was a corresponding index that I created earlier. Only when I added a FORCE INDEX clause to the query, it used a covering index. I've uploaded two files, one is the executed SQL queries and the other is the results. Can you tell why the query uses a covering-index only when a FORCE INDEX clause is added? The EXPLAIN shows that in both cases, the index dept_no_from_date_idx is being used anyway. To adapt myself to the standards of SO, I'm also writing the content of the two files here: The SQL queries: USE employees; /* Creating an index for an index-covered query */ CREATE INDEX dept_no_from_date_idx ON dept_emp (dept_no, from_date); /* Show `dept_emp` table structure, indexes and generic data */ SHOW TABLE STATUS LIKE "dept_emp"; DESCRIBE dept_emp; SHOW KEYS IN dept_emp; /* The EXPLAIN shows that the subquery doesn't use a covering-index */ EXPLAIN SELECT SQL_NO_CACHE * FROM dept_emp INNER JOIN ( /* The subquery should use a covering index, but isn't */ SELECT SQL_NO_CACHE emp_no, dept_no FROM dept_emp WHERE dept_no="d001" ORDER BY from_date DESC LIMIT 20000,50 ) AS `der` USING (`emp_no`, `dept_no`); /* The EXPLAIN shows that the subquery DOES use a covering-index, thanks to the FORCE INDEX clause */ EXPLAIN SELECT SQL_NO_CACHE * FROM dept_emp INNER JOIN ( /* The subquery use a covering index */ SELECT SQL_NO_CACHE emp_no, dept_no FROM dept_emp FORCE INDEX(dept_no_from_date_idx) WHERE dept_no="d001" ORDER BY from_date DESC LIMIT 20000,50 ) AS `der` USING (`emp_no`, `dept_no`); The results: -------------- /* Creating an index for an index-covered query */ CREATE INDEX dept_no_from_date_idx ON dept_emp (dept_no, from_date) -------------- Query OK, 331603 rows affected (33.95 sec) Records: 331603 Duplicates: 0 Warnings: 0 -------------- /* Show `dept_emp` table structure, indexes and generic data */ SHOW TABLE STATUS LIKE "dept_emp" -------------- +----------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+ | Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment | +----------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+ | dept_emp | InnoDB | 10 | Compact | 331883 | 36 | 12075008 | 0 | 21544960 | 29360128 | NULL | 2010-05-04 13:07:49 | NULL | NULL | utf8_general_ci | NULL | | | +----------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+ 1 row in set (0.47 sec) -------------- DESCRIBE dept_emp -------------- +-----------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------+---------+------+-----+---------+-------+ | emp_no | int(11) | NO | PRI | NULL | | | dept_no | char(4) | NO | PRI | NULL | | | from_date | date | NO | | NULL | | | to_date | date | NO | | NULL | | +-----------+---------+------+-----+---------+-------+ 4 rows in set (0.05 sec) -------------- SHOW KEYS IN dept_emp -------------- +----------+------------+-----------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | +----------+------------+-----------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ | dept_emp | 0 | PRIMARY | 1 | emp_no | A | 331883 | NULL | NULL | | BTREE | | | dept_emp | 0 | PRIMARY | 2 | dept_no | A | 331883 | NULL | NULL | | BTREE | | | dept_emp | 1 | emp_no | 1 | emp_no | A | 331883 | NULL | NULL | | BTREE | | | dept_emp | 1 | dept_no | 1 | dept_no | A | 7 | NULL | NULL | | BTREE | | | dept_emp | 1 | dept_no_from_date_idx | 1 | dept_no | A | 13 | NULL | NULL | | BTREE | | | dept_emp | 1 | dept_no_from_date_idx | 2 | from_date | A | 165941 | NULL | NULL | | BTREE | | +----------+------------+-----------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 6 rows in set (0.23 sec) -------------- /* The EXPLAIN shows that the subquery doesn't use a covering-index */ EXPLAIN SELECT SQL_NO_CACHE * FROM dept_emp INNER JOIN ( /* The subquery should use a covering index, but isn't */ SELECT SQL_NO_CACHE emp_no, dept_no FROM dept_emp WHERE dept_no="d001" ORDER BY from_date DESC LIMIT 20000,50 ) AS `der` USING (`emp_no`, `dept_no`) -------------- +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+-------------+ | 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 50 | | | 1 | PRIMARY | dept_emp | eq_ref | PRIMARY,emp_no,dept_no,dept_no_from_date_idx | PRIMARY | 16 | der.emp_no,der.dept_no | 1 | | | 2 | DERIVED | dept_emp | ref | dept_no,dept_no_from_date_idx | dept_no_from_date_idx | 12 | | 21402 | Using where | +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+-------------+ 3 rows in set (0.09 sec) -------------- /* The EXPLAIN shows that the subquery DOES use a covering-index, thanks to the FORCE INDEX clause */ EXPLAIN SELECT SQL_NO_CACHE * FROM dept_emp INNER JOIN ( /* The subquery use a covering index */ SELECT SQL_NO_CACHE emp_no, dept_no FROM dept_emp FORCE INDEX(dept_no_from_date_idx) WHERE dept_no="d001" ORDER BY from_date DESC LIMIT 20000,50 ) AS `der` USING (`emp_no`, `dept_no`) -------------- +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+--------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+--------------------------+ | 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 50 | | | 1 | PRIMARY | dept_emp | eq_ref | PRIMARY,emp_no,dept_no,dept_no_from_date_idx | PRIMARY | 16 | der.emp_no,der.dept_no | 1 | | | 2 | DERIVED | dept_emp | ref | dept_no_from_date_idx | dept_no_from_date_idx | 12 | | 37468 | Using where; Using index | +----+-------------+------------+--------+----------------------------------------------+-----------------------+---------+------------------------+-------+--------------------------+ 3 rows in set (0.05 sec) Bye

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• Warning: passing Argument 1 of "sqlite3_bind_text" from incompatible pointer type" What should I do

  - by Amarpreet

  Hi All, i am pretty new in iphone development. I have created one function to insert data into database. The code compiles successfully. But when comes to statement sqlite3_bind_text(sqlStatement, 1, [s UTF8String], -1, SQLITE_TRANSIENT); it does not do anything but hangs AND in warning it says "passing Argument 1 of "sqlite3_bind_text" from incompatible pointer type"" for all statements in Red colour The same code i am using to fetch the data from database and its working on other viewController. Below in the code. Its pretty straightforward. Please help guys. -(void) SaveData: (NSString *)FirstName: (NSString *)LastName: (NSString *)State: (NSString *)Street: (NSString *)PostCode { databaseName = @"Zen.sqlite"; NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDire ctory, NSUserDomainMask,YES); NSString *documentsDir=[documentPaths objectAtIndex:0]; databasePath=[documentsDir stringByAppendingPathComponent:databaseName]; sqlite3 *database; if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) { const char *sqlStatement = "insert into customers (FirstName, LastName, State, Street, PostCode) values(?, ?, ?, ?, ?)"; sqlite3_stmt *compiledStatement; sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL); sqlite3_bind_text(sqlStatement, 1, [FirstName UTF8String], -1, SQLITE_TRANSIENT); sqlite3_bind_text(sqlStatement,2,[LastName UTF8String],-1,SQLITE_TRANSIENT); sqlite3_bind_text(sqlStatement,3,[State UTF8String],-1,SQLITE_TRANSIENT); sqlite3_bind_text(sqlStatement,4,[Street UTF8String],-1,SQLITE_TRANSIENT); sqlite3_bind_text(sqlStatement,5,[PostCode UTF8String],-1,SQLITE_TRANSIENT); sqlite3_step(sqlStatement); sqlite3_finalize(compiledStatement); } sqlite3_close(database); }

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• How do I repass a function pointer in C++

  - by fneep

  Firstly, I am very new to function pointers and their horrible syntax so play nice. I am writing a method to filter all pixels in my bitmap based on a function that I pass in. I have written the method to dereference it and call it in the pixel buffer but I also need a wrapper method in my bitmap class that takes the function pointer and passes it on. How do I do it? What is the syntax? I'm a little stumped. Here is my code with all the irrelevant bits stripped out and files combined (read all variables initialized filled etc.). struct sColour { unsigned char r, g, b, a; }; class cPixelBuffer { private: sColour* _pixels; int _width; int _height; int _buffersize; public: void FilterAll(sColour (*FilterFunc)(sColour)); }; void cPixelBuffer::FilterAll(sColour (*FilterFunc)(sColour)) { // fast fast fast hacky FAST for (int i = 0; i < _buffersize; i++) { _pixels[i] = (*FilterFunc)(_pixels[i]); } } class cBitmap { private: cPixelBuffer* _pixels; public: inline void cBitmap::Filter(sColour (*FilterFunc)(sColour)) { //HERE!! } };

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• Deleting a non-owned dynamic array through a pointer

  - by ayanzo

  Hello all, I'm relatively novice when it comes to C++ as I was weened on Java for much of my undergraduate curriculum (tis a shame). Memory management has been a hassle, but I've purchased a number books on ansi C and C++. I've poked around the related questions, but couldn't find one that matched this particular criteria. Maybe it's so obvious nobody mentions it? This question has been bugging me, but I feel as if there's a conceptual point i'm not utilizing. Suppose: char original[56]; cstr[0] = 'a'; cstr[1] = 'b'; cstr[2] = 'c'; cstr[3] = 'd'; cstr[4] = 'e'; cstr[5] = '\0'; char *shaved = shavecstr(cstr); delete[] cstrn; where char* shavecstr(char* cstr) { size_t len = strlen(cstr); char* ncstr = new char[len]; strcpy(ncstr,cstr); return ncstr; } In that the whole point is to have 'original' be a buffer that fills with characters and routinely has its copy shaved and used elsewhere. To prevent leaks, I want to free up the memory held by 'shaved' to be used again after it passes through some arguments. There is probably a good reason for why this is restricted, but there should be some way to free the memory as by this configuration, there is no way to access the original owner (pointer) of the data.

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• set static member pointer variables

  - by Chris

  I'm trying to set a static pointer variable in a class but I'm getting these errors for each variable I try to set. error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2040: 'xscroll' : 'int' differs in levels of indirection from 'float *' error C2440: 'initializing' : cannot convert from 'float **' to 'int' Here is the code Enemy.h #include <windows.h> #include "Player.h" class Enemy { public: Enemy(float xPos, float yPos); Enemy(void); ~Enemy(void); //update the position of the user controlled object. void updatePosition(float timeFactor); //loads all the enemy textures void static loadTextures(); //creates a set number of enemies void static createEnemies(int numEnemies, Enemy * enemyArray); GLuint static enemyTex; static float * xscroll; static float * yscroll; static Player * player; private: bool checkCollison(float x, float y, int radius); float XPos; float YPos; }; trying to set variables Enemy::xscroll = &xscroll; Enemy::yscroll = &yscroll; Enemy::player = &player;

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• handling pointer to member functions within hierachy in C++

  - by anatoli

  Hi, I'm trying to code the following situation: I have a base class providing a framework for handling events. I'm trying to use an array of pointer-to-member-functions for that. It goes as following: class EH { // EventHandler virtual void something(); // just to make sure we get RTTI public: typedef void (EH::*func_t)(); protected: func_t funcs_d[10]; protected: void register_handler(int event_num, func_t f) { funcs_d[event_num] = f; } public: void handle_event(int event_num) { (this->*(funcs_d[event_num]))(); } }; Then the users are supposed to derive other classes from this one and provide handlers: class DEH : public EH { public: typedef void (DEH::*func_t)(); void handle_event_5(); DEH() { func_t f5 = &DEH::handle_event_5; register_handler(5, f5); // doesn't compile ........ } }; This code wouldn't compile, since DEH::func_t cannot be converted to EH::func_t. It makes perfect sense to me. In my case the conversion is safe since the object under this is really DEH. So I'd like to have something like that: void EH::DEH_handle_event_5_wrapper() { DEH *p = dynamic_cast<DEH *>(this); assert(p != NULL); p->handle_event_5(); } and then instead of func_t f5 = &DEH::handle_event_5; register_handler(5, f5); // doesn't compile in DEH::DEH() put register_handler(5, &EH::DEH_handle_event_5_wrapper); So, finally the question (took me long enough...): Is there a way to create those wrappers (like EH::DEH_handle_event_5_wrapper) automatically? Or to do something similar? What other solutions to this situation are out there? Thanks.

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• Problem in printing array of char pointer passing from Python

  - by Yan Cheng CHEOK

  My following C code works quite well, till my Python code trying to pass an array of char pointer to it. The output I obtain is The file_name is python-file Another 3 string is not being printed out. Anything I had missed out? C Code #include <iostream> #include "c_interface.h" int foo(const char* file_name, const char** names) { std::cout << "The file_name is " << file_name << std::endl; while (*names) { std::cout << "The name is " << *names << std::endl; names++; } return 0; } /* int main() { const char *c[] = {"123gh", "456443432", "789", 0}; foo("hello", c); getchar(); } */ Python Code #!c:/Python27/python.exe -u from ctypes import * name0 = "NAME0" name1 = "NAME1" name2 = "NAME2" names = ((c_char_p * 1024) * 4)() names[0].value = name0 names[1].value = name1 names[2].value = name2 names[3].value = 0 libc = CDLL("foo.dll") libc.foo("python-file", names)

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• Passing pointer into function, data appears initialized in function, on return appears uninitialize

  - by Luke Mcneice

  Im passing function GetCurrentDate() the pointer to a tm struct. Within that function I printf the uninitialized data, then the initialized. Expected results. However when i return the tm struct appears uninitialized. See console output bellow. What am i doing wrong? uninitialized date:??? ???-1073908332 01:9448278:-1073908376 -1217355836 initialized date:Wed May 5 23:08:40 2010 Caller date:??? ???-1073908332 01:9448278:-1073908376 -121735583 int main() { test(); } int test() { struct tm* CurrentDate; GetCurrentDate(CurrentDate); printf("Caller date:%s\n",asctime (CurrentDate)); return 1; } int GetCurrentDate(struct tm* p_ReturnDate) { printf("uninitialized date:%s\n",asctime (p_ReturnDate)); time_t m_TimeEntity; m_TimeEntity = time(NULL); //setting current time into a time_t struct p_ReturnDate = localtime(&m_TimeEntity); //converting time_t to tm struct printf("initialized date:%s\n",asctime (p_ReturnDate)); return 1; }

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• null pointer exception comparing two strings in java.

  - by David

  I got this error message and I'm not quite sure whats wrong: Exception in thread "main" java.lang.NullPointerException at Risk.runTeams(Risk.java:384) at Risk.blobRunner(Risk.java:220) at Risk.genRunner(Risk.java:207) at Risk.main(Risk.java:176) Here is the relevant bits of code (i will draw attention to the line numbers within the error message via comments in the code as well as inputs i put into the program while its running where relevant) public class Risk { ... public static void main (String[]arg) { String CPUcolor = CPUcolor () ; genRunner (CPUcolor) ; //line 176 ... } ... public static void genRunner (String CPUcolor) // when this method runs i select 0 and run blob since its my only option. Theres nothing wrong with this method so long as i know, this is only significant because it takes me to blob runner and because another one of our relelvent line numbers apears. { String[] strats = new String[1] ; strats[0] = "0 - Blob" ; int s = chooseStrat (strats) ; if (s == 0) blobRunner (CPUcolor) ; // this is line 207 } ... public static void blobRunner (String CPUcolor) { System.out.println ("blob Runner") ; int turn = 0 ; boolean gameOver = false ; Dice other = new Dice ("other") ; Dice a1 = new Dice ("a1") ; Dice a2 = new Dice ("a2") ; Dice a3 = new Dice ("a3") ; Dice d1 = new Dice ("d1") ; Dice d2 = new Dice ("d2") ; space (5) ; Territory[] board = makeBoard() ; IdiceRoll (other) ; String[] colors = runTeams(CPUcolor) ; //this is line 220 Card[] deck = Card.createDeck () ; System.out.println (StratUtil.canTurnIn (deck)) ; while (gameOver == false) { idler (deck) ; board = assignTerri (board, colors) ; checkBoard (board, colors) ; } } ... public static String[] runTeams (String CPUcolor) { boolean z = false ; String[] a = new String[6] ; while (z == false) { a = assignTeams () ; printOrder (a) ; boolean CPU = false ; for (int i = 0; i<a.length; i++) { if (a[i].equals(CPUcolor)) CPU = true ; //this is line 384 } if (CPU==false) { System.out.println ("ERROR YOU NEED TO INCLUDE THE COLOR OF THE CPU IN THE TURN ORDER") ; runTeams (CPUcolor) ; } System.out.println ("is this turn order correct? (Y/N)") ; String s = getIns () ; while (!((s.equals ("y")) || (s.equals ("Y")) || (s.equals ("n")) || (s.equals ("N")))) { System.out.println ("try again") ; s = getIns () ; } if (s.equals ("y") || s.equals ("Y") ) z = true ; } return a ; } ... } // This } closes the class The reason i don't think i should be getting a Null:pointerException is because in this line: a[i].equals(CPUcolor) a at index i holds a string and CPUcolor is a string. Both at this point definatly have a value neither is null. Can anyone please tell me whats going wrong?

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• How to handle 'this' pointer in constructor?

  - by Kyle

  I have objects which create other child objects within their constructors, passing 'this' so the child can save a pointer back to its parent. I use boost::shared_ptr extensively in my programming as a safer alternative to std::auto_ptr or raw pointers. So the child would have code such as shared_ptr<Parent>, and boost provides the shared_from_this() method which the parent can give to the child. My problem is that shared_from_this() cannot be used in a constructor, which isn't really a crime because 'this' should not be used in a constructor anyways unless you know what you're doing and don't mind the limitations. Google's C++ Style Guide states that constructors should merely set member variables to their initial values. Any complex initialization should go in an explicit Init() method. This solves the 'this-in-constructor' problem as well as a few others as well. What bothers me is that people using your code now must remember to call Init() every time they construct one of your objects. The only way I can think of to enforce this is by having an assertion that Init() has already been called at the top of every member function, but this is tedious to write and cumbersome to execute. Are there any idioms out there that solve this problem at any step along the way?

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• Strange error(dereferencing pointer to incomplete type)

  - by SMiX

  void get_cwd(char* buf) { char *result; current->fs->pwd; result = get_dentry_path(current->fs->pwd); memcpy(buf, result, strlen(result)+1); kfree(result); } error: dereferencing pointer to incomplete type The error points to current-fs-pwd; includes: #include <asm/stat.h> #include <linux/fs.h> #include <linux/file.h> #include <linux/module.h> #include <linux/kernel.h> #include <linux/string.h> #include <linux/dirent.h> #include <linux/sched.h> #include <asm/uaccess.h> #include <asm/current.h> #include <linux/path.h> If I type current-fs; on 5th line gcc don't give error on this line. The problem is with pwd field.

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• Initializing static pointer in templated class.

  - by Anthony

  This is difficult for me to formulate in a Google query (at least one that gives me what I'm looking for) so I've had some trouble finding an answer. I'm sure I'm not the first to ask though. Consider a class like so: template < class T > class MyClass { private: static T staticObject; static T * staticPointerObject; }; ... template < class T > T MyClass<T>::staticObject; // <-- works ... template < class T > T * MyClass<T>::staticPointerObject = NULL; // <-- cannot find symbol staticPointerObject. I am having trouble figuring out why I cannot successfully create that pointer object. Edit: The above code is all specified in the header, and the issue I mentioned is an error in the link step, so it is not finding the specific symbol.

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• Casting pointer to object to void * in C++

  - by JB

  I've been reading StackOverflow too much and started doubting all the code I've ever written, I keep thinking "Is that undefined behavour?" even in code that has been working for ages. So my question - Is it safe and well defined behavour to cast a pointer to an object (In this case abstract interface classes) to a void* and then later on cast them back to the original class and call method using them? I'm fully aware that the code that does this is probably awful. I wouldn't even consider writing it like this now (this is old code which I don't really want to change), so I'm not looking for a discussion of better ways to do this. I already know how to write it better if I ever did this again. But if it's actually broken to rely on this in C++ then I'll have to look at changing the code, if it's merely awful code then changing it won't be a priority. I would have had no doubts about something this simple a year or two ago but as my understanding of C++ increases I actually find I have more and more worries about code being safe under the standards even if it works perfectly well. Perhaps reading too much stack overflow is a bad thing for productivity sometimes :P

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• "assignment makes integer from pointer without a cast " warning in c

  - by mekasperasky

  #include<stdio.h> /* this is a lexer which recognizes constants , variables ,symbols, identifiers , functions , comments and also header files . It stores the lexemes in 3 different files . One file contains all the headers and the comments . Another file will contain all the variables , another will contain all the symbols. */ int main() { int i=0,j; char a,b[20],c[30]; FILE *fp1,*fp2; c[0]='"if"; c[1]="then"; c[2]="else"; c[3]="switch"; c[4]="printf"; c[5]="scanf"; c[6]="NULL"; c[7]="int"; c[8]="char"; c[9]="float"; c[10]="long"; c[11]="double"; c[12]="char"; c[13]="const"; c[14]="continue"; c[15]="break"; c[16]="for"; c[17]="size of"; c[18]="register"; c[19]="short"; c[20]="auto"; c[21]="while"; c[22]="do"; c[23]="case"; fp1=fopen("source.txt","r"); //the source file is opened in read only mode which will passed through the lexer fp2=fopen("lext.txt","w"); //now lets remove all the white spaces and store the rest of the words in a file if(fp1==NULL) { perror("failed to open source.txt"); //return EXIT_FAILURE; } i=0; while(!feof(fp1)) { a=fgetc(fp1); if(a!=' ') { b[i]=a; } else { for (j=0;j<23;j++) { if(c[j]==b) { fprintf(fp2, "%.20s\n", c[j]); continue ; } b[i]='\0'; fprintf(fp2, "%.20s\n", b); i=0; continue; } //else if //{ i=i+1; /*Switch(a) { case EOF :return eof; case '+':sym=sym+1; case '-':sym=sym+1; case '*':sym=sym+1; case '/':sym=sym+1; case '%':sym=sym+1; case ' */ } fclose(fp1); fclose(fp2); return 0; } This is my c code for lexical analysis .. its giving warnings and also not writing anything into the lext file ..

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• Pointer inside a struct / thread

  - by bruno

  Hi! I have this warning "warning: assignment from incompatible pointer type " in this line: data1->transformed_block[l] = &transformed_block[l]; - void print_message_function ( void *ptr ) { dt *data; data = (dt *) ptr; printf("Dentro da thread Numero0: %ld\n", data->L_norm_NewBlock); pthread_exit(0); } typedef struct data_thread { long L_norm_NewBlock; int Bsize_X; int Bsize_Y; int *transformed_block[MAX_LEVEL]; long L_norm_OrigBlock; } dt; void function() { int *transformed_block[MAX_LEVEL]; pthread_t thread1; dt *data1; pthread_attr_t attr; pthread_attr_init(&attr); //Fills structure data1 = (dt *) malloc(sizeof(dt)); data1->transformed_block[l] = &transformed_block[l]; data1->L_norm_NewBlock=0; data1->Bsize_Y = Bsize_Y; data1->Bsize_X = Bsize_X; pthread_create(&thread1, &attr, (void *) &print_message_function, (void *) &data1); } I want to get rid of that warning, and the values i get inside the thread are wrong. For example data1-L_norm_NewBlock=0; in the thread guives me a differente value (not 0 like it should be).

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• Updating Pointer using signals and slots

  - by Umesha MS

  Hi, I am very new to the QT; please help me to solve the problem. I am using thread to perform intensive operation in back ground. Meanwhile I want to update the UI, so I am using SIGNALS and SLOTS. To update UI I emit a signal and update UI. Let us consider bellow sample code, struct sample { QString name; QString address; }; void Update(sample *); void sampleFunction() { sample a; a.name = "Sachin Tendulkar"; a.address = "India" emit Update(&a); } In the above code we are creating a local object and passing the address of local object. In the QT document, it says that when we emit a signal it will be placed in the queue and late it will be delivered to the windows. Since my object is in local scope it will be delete once it goes out of the scope. Please tell me a way to send a pointer in a signal.

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• C++: why a self pointer of a struct automatically changes to void*

  - by Stone

  struct ptr{ int node; ptr *next; ptr(){} ptr(int _node, ptr *_next){ node=_node; next=_next; } }; struct list_t{ ptr *sht; int size; void push(int node){ size++; sht=new ptr(node,sht); } }shthead[100001], comp[200001], tree[200001]; The struct ptr is a smart pointer, be used as a linked list. But when I debug the code in gdb, I found that the ptr*'s were all converted to void*. GDB output: (gdb) pt ptr type = struct ptr { int node; void *next; public: ptr(void); ptr(int, void *); } However, I can still see the data of the struct if I covert them back to ptr* in gdb. What's the reason for this please?

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• Accessing derived class members with a base class pointer

  - by LRB

  I am making a simple console game in C++ I would like to know if I can access members from the 'entPlayer' class while using a pointer that is pointing to the base class ( 'Entity' ): class Entity { public: void setId(int id) { Id = id; } int getId() { return Id; } protected: int Id; }; class entPlayer : public Entity { string Name; public: entPlayer() { Name = ""; Id = 0; } void setName(string name) { Name = name; } string getName() { return Name; } }; Entity *createEntity(string Type) { Entity *Ent = NULL; if (Type == "player") { Ent = new entPlayer; } return Ent; } void main() { Entity *ply = createEntity("player"); ply->setName("Test"); ply->setId(1); cout << ply->getName() << endl; cout << ply->getId() << endl; delete ply; } How would I be able to call ply-setName etc? OR If it's not possible that way, what would be a better way?

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• NULL pointer dereference in swiotlb_unmap_sg_attrs() on disk IO

  - by Inductiveload

  I'm getting an error I really don't understand when reading or writing files using a PCIe block device driver. I seem to be hitting an issue in swiotlb_unmap_sg_attrs(), which appears to be doing a NULL dereference of the sg pointer, but I don't know where this is coming from, as the only scatterlist I use myself is allocated as part of the device info structure and persists as long as the driver does. There is a stacktrace to go with the problem. It tends to vary a bit in exact details, but it always crashes in swiotlb_unmap_sq_attrs(). I think it's likely I have a locking issue, as I am not sure how to handle the locks around the IO functions. The lock is already held when the request function is called, I release it before the IO functions themselves are called, as they need an (MSI) IRQ to complete. The IRQ handler updates a "status" value, which the IO function is waiting for. When the IO function returns, I then take the lock back up and return to request queue handling. The crash happens in blk_fetch_request() during the following: if (!__blk_end_request(req, res, bytes)){ printk(KERN_ERR "%s next request\n", DRIVER_NAME); req = blk_fetch_request(q); } else { printk(KERN_ERR "%s same request\n", DRIVER_NAME); } where bytes is updated by the request handler to be the total length of IO (summed length of each scatter-gather segment).

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• Function returning pointer to struct

  - by GammaGuy

  I am having some issues with code that is returning a pointer to a struct declared inside a class. Here is my code so far: SortedList.h #ifndef SORTEDLIST_H #define SORTEDLIST_H class SortedList{ public: SortedList(); ... private: struct Listnode { Student *student; Listnode *next; }; static Listnode *copyList (Listnode *L); }; #endif SortedList.cpp #include "SortedList.h" ... // Here is where the problem lies Listnode SortedList::*copyList(Listnode *L) { return 0; // for NULL } Apparently, the copy list method wont compile. I am using Microsoft Visual Studio and the compiler tells me that "Listnode" is unidentified. When I try to compile, here is whhat I get: 1>------ Build started: Project: Program3, Configuration: Debug Win32 ------ 1> SortedList.cpp 1>c:\users\owner\documents\college\fall 2012\cs 368 - learn c++\program3\program3\sortedlist.cpp(159): error C2657: 'SortedList::*' found at the start of a statement (did you forget to specify a type?) 1>c:\users\owner\documents\college\fall 2012\cs 368 - learn c++\program3\program3\sortedlist.cpp(159): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 1>c:\users\owner\documents\college\fall 2012\cs 368 - learn c++\program3\program3\sortedlist.cpp(159): error C2065: 'L' : undeclared identifier 1>c:\users\owner\documents\college\fall 2012\cs 368 - learn c++\program3\program3\sortedlist.cpp(159): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 1>c:\users\owner\documents\college\fall 2012\cs 368 - learn c++\program3\program3\sortedlist.cpp(159): fatal error C1903: unable to recover from previous error(s); stopping compilation ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== Help would be greatly appreciated...ASAP

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• Public class: Makes pointer from integer without cast

  - by meridimus

  I have written a class to help save and load data for the sake of persistence for my iPhone application but I have a problem with some NSUIntegers that I'm passing across. Basically, I have the code to use pointers, but eventually it has to start out being an actual value right? So I get this error warning: passing argument 1 of 'getSaveWithCampaign:andLevel:' makes pointer from integer without a cast My code is laid out like so. (Persistence is the name of the class) NSDictionary *saveData = [Persistence getSaveWithCampaign:currentCampaign andLevel:[indexPath row]]; Here's Persistence.m #import "Persistence.h" @implementation Persistence + (NSString *)dataFilePath { NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; return [documentsDirectory stringByAppendingPathComponent:kSaveFilename]; } + (NSDictionary *)getSaveWithCampaign:(NSUInteger *)campaign andLevel:(NSUInteger *)level { NSString *filePath = [self dataFilePath]; if([[NSFileManager defaultManager] fileExistsAtPath:filePath]) { NSDictionary *saveData = [[NSDictionary alloc] initWithContentsOfFile:filePath]; NSString *campaignAndLevelKey = [self makeCampaign:campaign andLevelKey:level]; NSDictionary *campaignAndLevelData = [saveData objectForKey:campaignAndLevelKey]; [saveData release]; return campaignAndLevelData; } else { return nil; } } + (NSString *)makeCampaign:(NSUInteger *)campaign andLevelKey:(NSUInteger *)level { return [[NSString stringWithFormat:@"%d - ", campaign+1] stringByAppendingString:[NSString stringWithFormat:@"%d", level+1]]; } @end

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• When to use pointer to a class and when to just instantiate it as a variable

  - by Enders

  Im sort of confused by it. The best I could find was reading through the cplusplus.com tutorial and all they have to say about pointers to classes. "It is perfectly valid to create pointers that point to classes. We simply have to consider that once declared, a class becomes a valid type, so we can use the class name as the type for the pointer" Which tells me nothing about when to use them over the normal instantiation. I've seen the - operator many times, and looked at some codes but cant really decipher why they did it. Generic examples will be appreciated; but more specifically related to gui programming. Its where I encountered it first. QGridLayout *mainLayout = new QGridLayout; mainLayout->addWidget(nameLabel, 0, 0); mainLayout->addWidget(nameLine, 0, 1); mainLayout->addWidget(addressLabel, 1, 0, Qt::AlignTop); mainLayout->addWidget(addressText, 1, 1); Why not QGridLayout mainLayout mainLayout.addWidget ... (It doesnt compile if I change the sample code to that and try it but you get the point) Thanks in advance

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