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• const read only local copies

  - by robUK

  Hello gcc 4.4.4 c89 I am just wondering is it worth passing a const into a function. i.e. void do_something(const char *dest, const int size) The size is a read-only so I don't want to change it. However, some developers never have this as const has it is a local copy that is being used. The pointer is const as you can change the value in the calling routine. I always have a const on read-only local copies, as it confirms to anyone reading my code that it is a read-only variable. And also, when coding I don't make the mistake of changing it without realizing. Many thanks for any suggestions,

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• Perl, treat string as binary byte array

  - by Mike

  In Perl, is it appropriate to use a string as a byte array containing 8-bit data? All the documentation I can find on this subject focuses on 7-bit strings. For instance, if I read some data from a binary file into $data my $data; open FILE, "<", $filepath; binmode FILE; read FILE $data 1024; and I want to get the first byte out, is substr($data,1,1) appropriate? (again, assuming it is 8-bit data) I come from a mostly C background, and I am used to passing a char pointer to a read() function. My problem might be that I don't understand what the underlying representation of a string is in Perl.

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• How to modify TList<record> value?

  - by Astronavigator

  How to modify TList < record value ? type TTest = record a,b,c:Integer end; var List:TList<TTest>; A:TTest; P:Pointer; .... .... List[10] := A; <- OK List[10].a:=1; <- Here compiler error : Left side cannot be assined to P:=@List[10]; <- Error: Variable requied

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• What's the purpose of having a separate "operator new[]" ?

  - by sharptooth

  Looks like operator new and operator new[] have exactly the same signature: void* operator new( size_t size ); void* operator new[]( size_t size ); and do exactly the same: either return a pointer to a big enough block of raw (not initialized in any way) memory or throw an exception. Also operator new is called internally when I create an object with new and operator new[] - when I create an array of objects with new[]. Still the above two special functions are called by C++ internally in exactly the same manner and I don't se how the two calls can have different meanings. What's the purpose of having two different functions with exactly the same signatures and exactly the same behavior?

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• got a question about Linked-List in java code.

  - by glacier89

  Linked-List: Mirror Consider the following private class for a node of a singly-linked list of integers: private class Node{ public int value; public Node next; } A wrapper-class, called, ListImpl, contains a pointer, called start to the first node of a linked list of Node. Write an instance-method for ListImpl with the signature: public void mirror(); That makes a reversed copy of the linked-list pointed to by start and appends that copy to the end of the list. So, for example the list: start 1 2 3 after a call to mirror, becomes: start 1 2 3 3 2 1 Note: in your answer you do not need to dene the rest of the class for ListImpl just the mirror method.

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• How to debug macruby?

  - by Dan

  Hi, I've encountered an inconsistent bug with MacRuby and have no idea how to go about debugging this. If anyone could help would be great. I don't know if this is due to my own code or is it a bug in the MacRuby framework. I have a feeling it's my own code, something about over-retaining a piece of memory and hence the garbage collection failed. This is the error from Xcode. Thanks. CSV Wizard(30245,0x7fff704f7ca0) malloc: resurrection error for object 0x20199da20 while assigning {conservative-block}[196608](0x302360060)[117616] = Array[64](0x20199da20) garbage pointer stored into reachable memory, break on auto_zone_resurrection_error to debug CSV Wizard(30245,0x103781000) malloc: garbage block 0x20199da20(Array[64]) was over-retained during finalization, refcount = 1 This could be an unbalanced CFRetain(), or CFRetain() balanced with -release. Break on auto_zone_resurrection_error() to debug. CSV Wizard(30245,0x103781000) malloc: fatal resurrection error for garbage block 0x20199da20(Array[64]): over-retained during finalization, refcount = 1

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• how to open many files simultaneously for reading in c

  - by monkeyking

  I'm trying to port some of my c++ code into c. I have the following construct class reader{ private: FILE *fp; alot_of_data data;//updated by read_until() method public: reader(const char*filename) read_until(some conditional dependent on the contents of the file, and the arg supplied) } Im then instantiating hundreds of these object and iterate over them using several 'read_until()' for each file until allfiles is at eof. I'm failing to see any clever way to do this in c, the only solution I can come up with is making an array of FILE pointers, and do the same with all the private member data from my class. But this seems very messy, can I implement the functionality of my class as a function pointer, or anything better, I think I'm missing a fundamental design pattern? The files are way to big to have all in memory, so reading everything from every file is not feasible Thanks

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• use callback function to report stack backtrace

  - by user353394

  Assume I have the following: typedef struct { char *name; char binding; int address; } Fn_Symbol //definition of function symbol static Fn_Symbol *fnSymbols; //array of function symbols in a file statc int total; //number of symbol functions in the array and file static void PrintBacktrace(int sigum, siginfo_t * siginfo, void *context) { printf("\nSignal received %d (%s)\n", signum, strsignal(signum)); const int eip_index = 14; void *eip = (void *)((struct ucontext *)context)->uc_mcontext.gregs[eip_index]; printf("Error at [%p] %s (+0x%x), eip, fnName, offset from start); //????? exit(0); } I have this so far, but what is the best way using the fnSymbols static global pointer to identify the function where the error occured and then back trace through the stack to identify each calling function by address, name, and offset?

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• Avoiding Nested Blocks

  - by Helium3

  If there is a view controller that wants to execute a number of block based tasks one at a time, how can the control be given back to the view controller after a completion block has executed. Lets say ViewControllerOne wants to execute a number of tasks, each relying on the result of the previous one, how would this control be given back to the viewcontroller after each completion block has been executed? I started thinking about this and I was heading towards a deeply nested block pattern that will surely only cause confusion to whoever else reads or tests it. A task executes and the completion block returns the result or error which is needed by the next task, which has its own completion task, that the next task relies on and so forth. How can the control be managed in one place, the viewcontroller? Would the completion block just call the next function that handles the next task, using a pointer to the view controller?

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• Converting between unsigned and signed int safely

  - by polemic

  I have an interface between a client and a server where a client sends (1) an unsigned value, and (2) a flag which indicates if value is signed/unsigned. Server would then static cast unsigned value to appropriate type. I later found out that this is implementation defined behavior and I've been reading about it but I couldn't seem to find an appropriate solution that's completely safe? I've read about type punning, pointer conversions, and memcpy. Would simply using a union type work? A UnionType containing signed and unsigned int, along with the signed/unsigned flag. For signed values, client sets the signed part of the union, and server reads the signed part. Same for the unsigned part. Or am I completely misunderstanding something? Side question: how do I know the specific behavior in this case for a specific scenario, e.g. windriver diab on PPC? I'm a bit lost on how to find such documentation.

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• C# SendMessage to C++ WinProc

  - by jws

  I need to send a string from C# to a C++ WindowProc. There are a number of related questions on SO related to this, but none of the answers have worked for me. Here's the situation: PInvoke: [DllImport("user32", CharSet = CharSet.Auto)] public extern static int SendMessage(IntPtr hWnd, uint wMsg, IntPtr wParam, string lParam); C#: string lparam = "abc"; NativeMethods.User32.SendMessage(handle, ConnectMsg, IntPtr.Zero, lparam); C++: API LRESULT CALLBACK HookProc (int code, WPARAM wParam, LPARAM lParam) { if (code >= 0) { CWPSTRUCT* cwp = (CWPSTRUCT*)lParam; ... (LPWSTR)cwp->lParam <-- BadPtr ... } return ::CallNextHookEx(0, code, wParam, lParam); } I've tried a number of different things, Marshalling the string as LPStr, LPWStr, also tried creating an IntPtr from unmanaged memory, and writing to it with Marshal.WriteByte. The pointer is the correct memory location on the C++ side, but the data isn't there. What am I missing?

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• When to pass by value?

  - by Dervin Thunk

  Dear all. I was wondering if there are examples of situations where you would purposefully pass an argument by value in C. Let me rephrase. When do you purposefully use C's pass-by-value for large objects? Or, when do you care that the object argument is fully copied in a local variable? EDIT: Now that I think about it, if you can avoid pointers, then do. Nowadays, "deep" copying is possible for mostly everything in small apps, and shallow copying is more prone to pointer bugs. Maybe.

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• Why does accessing a member of a malloced array of structs seg fault?

  - by WSkinner

  I am working through Learn C The Hard Way and am stumped on something. I've written a simplified version of the problem I am running into to make it easier to get down to it. Here is the code: #include <stdlib.h> #define GROUP_SIZE 10 #define DATA_SIZE 64 struct Dummy { char *name; }; struct Group { struct Dummy **dummies; }; int main() { struct Group *group1 = malloc(sizeof(struct Group)); group1->dummies = malloc(sizeof(struct Dummy) * GROUP_SIZE); struct Dummy *dummy1 = group1->dummies[3]; // Why does this seg fault? dummy1->name = (char *) malloc(DATA_SIZE); return 0; } when I try to set the name pointer on one of my dummies I get a seg fault. Using valgrind it tells me this is uninitialized space. Why is this?

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• Strange error with CreateCompatibleDC

  - by sevaxx

  Maybe this is a foolish question, I can't see why I can not get a DC created in the following code : HBITMAP COcrDlg::LoadClippedBitmap(LPCTSTR pathName,UINT maxWidth,UINT maxHeight) { HBITMAP hBmp = (HBITMAP)::LoadImage(NULL, pathName, IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE | LR_CREATEDIBSECTION); if (!hBmp) return NULL; HDC hdc = (HDC)GetDC(); HDC hdcMem = CreateCompatibleDC(hdc); if (!hdcMem) { DWORD err = GetLastError(); } ... ... ... The bitmap hBmp is loaded fine and hdc has a valid value. But the call to CreateCompatibleDC() returns a NULL pointer. Then, GetLastError() returns 0 ! Anybody can guess what's going on here , please ? PS : There are no memory allocations or GDI routines called before this one...so I think memory leaks should be ruled out.

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• How do I modify the -encoding argument to javac in the Android Ant build system

  - by Paul Butcher

  Apologies if this is a stupid question - I'm an Android and Ant newbie. I have utf8 encoded source files that I need to compile with the Android Ant build system. By default, the encoding is set to ascii. I'd be very grateful for a pointer to whatever I need to do to let the build system know that my files are utf8. Incidentally, it works fine if I build in Eclipse, but I need to build from the command line. Thanks!

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• Swap bits in c++ for a double

  - by hidayat

  Im trying to change from big endian to little endian on a double. One way to go is to use double val, tmp = 5.55; ((unsigned int *)&val)[0] = ntohl(((unsigned int *)&tmp)[1]); ((unsigned int *)&val)[1] = ntohl(((unsigned int *)&tmp)[0]); But then I get a warning: "dereferencing type-punned pointer will break strict-aliasing rules" and I dont want to turn this warning off. Another way to go is: #define ntohll(x) ( ( (uint64_t)(ntohl( (uint32_t)((x << 32) >> 32) )) << 32) | ntohl( ((uint32_t)(x >> 32)) ) ) val = (double)bswap_64(unsigned long long(tmp)); //or val = (double)ntohll(unsigned long long(tmp)); But then a lose the decimals. Anyone know a good way to swap the bits on a double without using a for loop?

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• Cannot implicitly convert type 'char*' to 'bool'

  - by neeraj

  i was trying to passing pointer value in the function , i really got stuck here I am a beginner , not getting what value should be put this is programme from the reference of the book "Cracking the coding interview " By Gayle Laakmann McDowell, class Program { unsafe void reverse(char *str) { char* end = str; char tmp; if (str) //Cannot implicitly convert type 'char*' to 'bool' { while(*end) //Cannot implicitly convert type 'char*' to 'bool' { ++end; } --end; while(str<end) { tmp = *str; *str+= *end; *end-= tmp; } } } public static void Main(string[] args) { } }

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• How does C++ free the memory when a constructor throws an exception and a custom new is used

  - by Joshua

  I see the following constructs: new X will free the memory if X constructor throws. operator new() can be overloaded. The canonical definition of an operator new overload is void *operator new(heap h) and the corrisponding operator delete. The most common operator new overload is pacement new, which is void *operator new(void *p) { return p; } You almost always cannot call delete on the pointer given to placement new. This leads to a single question. How is memory cleaned up when X constructor throws and an overloaded new is used?

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• Jquery toggle should expand after Page reload

  - by James123

  I wrote below code for Collapse/Expand some section. It is working fine. Finally If I click "Save" button and I am re-loading page again in asp.net. So then sections are going default Colleapse again. I need them back to expand. How can I do that? $(function() { $('tr.subCategory') .css("cursor", "pointer") .attr("title", "Click to expand/collapse") .click(function() { $(this).siblings('.RegText-' + this.id).toggle(); }); $('tr[@class^=RegText-]').hide().children('td'); })

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• JQuery Autocomplete - Stop mouseover+Return submitting data

  - by ILT

  I'm using JQuery Autocomplete (bassistance) and have run into a problem. If the mouse rolls over one of the autocomplete suggestions and the user hits the return key (rather than clicking to make selection), the form is submitted and goes to whatever link was rolled over at the time. This is a problem as people click in the textbox, and when typing their search, leave the pointer where the autocomplete popup appears. So when they hit enter, it doesn't do the search for whatever they typed in the box but whatever was highlighted in the autocomplete suggestions. Is there a way to stop this? Using Google as the functionality I'm after... So just to clarify - I want selections via mouse and keyboard to go to the same place, but if the UP or DOWN arrow has not been pressed (user not selected an autocomplete option via the keyword), dont go to the URL specified in the autosuggest - instead submit the form (traditional method without JQuery) based on what has been typed in the textbox. I hope I'm explaining this clearly? :S

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• BufferedImage Help

  - by Eddy Freeman

  I posted a question in sun java forums sometime ago and i am finding it hard to understand the first response i received from the replier though it seems he gave me the correct approach to my problem. The link to the question is: http://forums.sun.com/thread.jspa?threadID=5436562&tstart=0 Someone replied that i should use BufferedImage and make tiles. I don't really understand what the tiles mean in connection with the BufferedImage. I would like someone to explain to me what the tiles are and how they are created in the BufferedImage. I have searched the web for a while but couldn't find any link that can help me understanding the basics of the tiles and creating the tiles. Any pointer to a site is also appreciated. I need help in understanding the tiles in connection with the BufferedImage and also how they are created.

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• Removing a UIView from its superView and expanding its frame to full screen

  - by Magic Bullet Dave

  I have an object that is a subclass of UIView that can be added to a view hierarchy as a subView. I want to be able to remove the UIView from its superView and add it as a subView of the main window and then expand to full screen. Something along the lines of: // Remove from superView and add to mainWindow [self retain]; [self removeFromSuperView]; [self addSubView:mainWindow]; // Animate to full screen [UIView beginAnimations:@"expandToFullScreen" context:nil]; [UIView setAnimationDuration:1.0]; self.frame = [[UIScreen mainScreen] applicationFrame]; [UIView commitAnimations]; [self release]; Firstly am I on the right lines? Secondly, is there an easily way for the object to get a pointer to the mainWindow? Thanks Dave

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• ASP.NET MVC, JSON & non JavaScript clients

  - by redsquare

  I need to ensure that an application I am developing is accessable and also works with JavaScript turned off. I just need a pointer to assist with the following. I had 3 'chained' select boxes and I wanted JavaScript enabled clients to have a nice Ajax experience. I can easily write the required functionality to populate the chained boxes on the change event of the preceeding select using jQuery and JSON with a WCF service. However what about the non JavaScript client? Would I wrap a submit next to the select and place these inside their own form to post back with a certain action or different querstring parameter? Can the same controller give me a partial JSON response as well as feeding the full HTML response. Can anyone point me to a good demo that utilises both JSON and normal HTTP posts to produce the same result in ASP.NET MVC. All ASP.NET MVC demo/examples I see forget about the non JavaScript enabled client.

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• Socket programming question

  - by dfddf

  I am given the following declaration: char inbuff[500], *ptr; int n, bufferlen; Write a program segement to receive a message having 500 bits from the TCP socket sock and store this message in inbuff. My answer is: n = recv( sock, inbuff, strlen( inbuff ), 0 ); However, I am not sure why *ptr is given in the declaration. So, I would like ask, what is the purpose of the pointer in this question?? Or my program segement is wrong? Thank you for all of yours help first!

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• C# PropertyGrid drag drop

  - by gametheoryonline

  I'm trying to implement drag/drop support to a propertygrid in C# using VS2005 (.NET 2.0). The propertygrid can handle the dragenter etc. events, but there doesn't seem to be a way to get the griditem under the pointer during a drag event. The best I've been able to get so far is to use the selectedgriditem property to retrieve a custom propertydescriptor and set the value, but this requires a grid item to already be selected before starting the drag/drop operation. Has anyone had any luck with implementing this? Thanks :-)

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