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• Understanding c++ block of code

  - by kotoko

  I was given a c++ main and have to code it so it works. I am having some trouble understanding the code as I am a bit new to cpp. Here is the code int main(int argc, char *argv[]) { Class::setAtribute("string"); Class(Class::CONSTANT) << "starting up..."; } Some questions: How can the first line work with no variables? Is it static? The second line is really strange for me, what I can make out is a Constructor that takes in a class constante and then prints it out somehow? If someone could explain me this bit of code it would be great! Thanks in advance.

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• C++ Structure within itself?

  - by Douglas

  I've been trying to port this code to python, but there is something I do not quite understand in C++ (I do know a bit of C++ but this is beyond me): typedef struct huffnode_s { struct huffnode_s *zero; struct huffnode_s *one; unsigned char val; float freq; } huffnode_t; What I don't get is how huffnode_s can be within itself, I've never seen this before and don't quite understand it. What does this mean, and if someone can, what would be the python equivalent?

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• Can anyone tell me were I am making mistake in the snippet

  - by Solitaire

  public partial class Form1 : Form { [DllImport("coredll.dll")] static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong); const int GWL_WNDPROC = -4; public delegate int WindProc(IntPtr hWnd, uint msg, long Wparam, long lparam); public Form1() { InitializeComponent(); WindProc SampleProc = new WindProc (SubclassWndProc); SetWindowLong(this .Handle , GWL_WNDPROC, SampleProc.Method .MethodHandle.Value.ToInt32()); } public int SubclassWndProc(IntPtr hwnd, uint msg, long Wparam, long lparam) { return 1; } Here is the sample which i was trying to take the window procedure of a form, this is how i do in C++ i get the windwproc easlily if i try the same in C# .net 3.5 i am unable to get the window proc,, after calling SetWindowLong API application hangs and it pops up some dont send report... i have read this is the way to get the window proc.. please let me know were i am making mistake...

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• What is on the 68000 stack when classic MacOS enters a program?

  - by John Källén

  I'm trying to understand an old classic Mac application's entry point. I've disassembled the first CODE resource (not CODE#0, which is the jump table). The code refers to some variables off the stack: a word at 0004(A7), an array of long words of starting at 000C(A7) whose length is the value at 0004(A7), and a final long word beyond that array that seems to be a pointer to a character string. The array of long words looks like strings at first glance, so it looks superficially like we're dealing with an (int argc, char ** argv) situation, except the "argv" array is inline in the stack frame. What should a program be expecting on its stack / registers when it first gets called by the Mac OS?

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• Does C++ have a proper implementation of interface that does not use vtable?

  - by gilbertc

  Does C++ have a proper implementation of interface that does not use vtable? for example class BaseInterface{ public: virtual void func() const = 0; } class BaseInterfaceImpl:public BaseInterface{ public: void func(){ std::cout<<"called."<<endl; } } BaseInterface* obj = new BaseInterfaceImpl(); obj->func(); the call to func at the last line goes to vtable to find the func ptr of BaseInterfaceImpl::func, but is there any C++ way to do that directly as the BaseInterfaceImpl is not subclassed from any other class besides the pure interface class BaseInterface? Thanks. Gil.

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• Query on the scope of local variables in C

  - by darkie15

  All, Consider the following code: void func(void) { int a; printf ("%d", a); } int main(int argc, char **argv) { int a = 3; func(); printf("%d", a); } According to my understanding, the output should be: <junk value><3> Can anyone please confirm my understanding? My basic query is, does the compiler refer to the outer scope for a variable that has been declared but not defined? Regards, darkie

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• How can I load a SQLITE database from a buffer with the C API ?

  - by rockeye

  Hello, I am trying to load a database from the memory instead of opening a .sqlite file. I have read the C/C++ API reference but I can not find the proper method. The buffer I am trying to load is simply an sqlite file loaded in memory. I just want to use this buffer (a const char* array) without using the filesystem (I could have saved this buffer in a file, then load the file, but no). First, I create a memory DB : mErrorCode = sqlite3_open_v2(":memory:", &mSqlDatabase, lMode, NULL); This returns SQLITE_OK, then I tried to use the buffer as a statement and call preparev2(MyDB, MyBufferData, MyBufferLength, MyStatement, NULL) but it's not really a statement, and it returns an error. Same result if I call directly exec(MyDB, MyBufferData, NULL, NULL, NULL); I guess there is an appropriate method to achieve this as it might be common to load a DB from a stream or from decrypted data... Thanks.

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• When do I need to deallocate memory? C++

  - by extintor

  I am using this code inside a class to make a webbrowser control visit a website: void myClass::visitWeb(const char *url) { WCHAR buffer[MAX_LEN]; ZeroMemory(buffer, sizeof(buffer)); MultiByteToWideChar(CP_ACP, MB_ERR_INVALID_CHARS, url, strlen(url), buffer, sizeof(buffer)-1); VARIANT vURL; vURL.vt = VT_BSTR; vURL.bstrVal = SysAllocString(buffer); // webbrowser navigate code... VariantClear(&vURL); } Do I need to do some memory deallocation here?, I see vURL is being deallocated by VariantClear but should I deallocate memory for buffer? I've been told that in another bool I have in the same app I shouldn't deallocate anything because everything clear out when the bool return true/false, but what happens on this void?

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• small string optimization for vector?

  - by BuschnicK

  I know several (all?) STL implementations implement a "small string" optimization where instead of storing the usual 3 pointers for begin, end and capacity a string will store the actual character data in the memory used for the pointers if sizeof(characters) <= sizeof(pointers). I am in a situation where I have lots of small vectors with an element size <= sizeof(pointer). I cannot use fixed size arrays, since the vectors need to be able to resize dynamically and may potentially grow quite large. However, the median (not mean) size of the vectors will only be 4-12 bytes. So a "small string" optimization adapted to vectors would be quite useful to me. Does such a thing exist? I'm thinking about rolling my own by simply brute force converting a vector to a string, i.e. providing a vector interface to a string. Good idea?

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• Copying pointers in C++

  - by tunnuz

  Hello, I have a class A containing two pointers to objects of another class B. I want to initialize one pointer or the other depending on which one is passed to init(), which also takes other parameters. My situation is thus the following: class A { public: A(); init(int parameter, int otherParameter, B* toBeInitialized); protected: B* myB; B* myOtherB; }; Now my point is that I want to call init() as: init(640, 480, this->myB); or init(640, 480, this->myOtherB); Now, my init is implemented as: void init( int parameter, int otherParameter, B* toBeInitialized ) { toBeInitialized = someConstructorFunction(parameter, otherParameter); } The problem is that the two pointers are not initialized, I suspect that toBeInitialized is overwritten, but the original parameter is not modified. I am doing something wrong? Should I use references to pointers? Thank you Tommaso

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• Excel VBA : Changing string in cells

  - by user1265125

  I have cells with data like these: ABCD123XYZ MPOP345MLU . . . . What I want to do is, to remove the 3rd and 4th character from all these cells, hence giving AB123XYZ MP345MLU How do I do this in VBA? I have no idea about this language, and if someone can guide me in the right direction, it'd be great :) I understand I have to: 1. Declare 2 string variables st1 and st2 2. Store data from cell A1 into the variable st1 3. Copy all but the 2nd and 3rd char into str2 4. Output Str2 into B1 5. Move to A2

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• SQL Server 2008 Stored Procedure

  - by user238319

  I cannot store the date data type variables using stored procedure. My code is: ALTER PROCEDURE [dbo].[Access1Register] -- Add the parameters for the stored procedure here @MobileNumber int, @CitizenName varchar(50), @Dob char(8), @VerificationCode int AS BEGIN -- SET NOCOUNT ON added to prevent extra result sets from -- interfering with SELECT statements. SET NOCOUNT ON; -- Insert statements for procedure here select CAST(@dob As DATE) Insert Into Access1 (MobileNo,CitizenName,Dob,VerificationCode) values(@MobileNumber,@CitizenName,@Dob,@VerificationCode) go If I exec this procedure it is executing, but there is an error occured in the date type variable. It's raising the error as invalid item '-'.

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• How do I get the size of the boost buffer

  - by Anonymous

  I am trying to make an asynchronised server in visual studio and I use boost::asio::async_read(m_socket, boost::asio::buffer(m_buffer), boost::bind(&tcp_connection::handle_read, shared_from_this(), boost::asio::placeholders::error)); to get the buffer to be put in m_buffer boost::array<char, 256> m_buffer; but how do I get the size of this thing, m_buffer? size() didn't work, end() didn't work.. Any help would be fantastic. Thanks in advance.

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• sysklogd ignores my log facilities

  - by Synther Lawrence

  I'm using sysklogd 1.5.5. All I want is to get local0 entries in /var/log/vr file. My conf: *.*;local0.none /var/log/messages local0.* /var/log/vr When I do logger -p local0.info "local0 test from logger" the message appear in /var/log/vr file. That's ok. But the following sends message to /var/log/messages instead of /var/log/vr: #include <stdlib.h> #include <syslog.h> int main(int argc, char const* argv[]) { openlog(NULL, LOG_PID, LOG_LOCAL0); syslog(LOG_INFO, "local0 test from app\n"); closelog(); return 0; } Where am I wrong?

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• EXC_BAD_ACCESS from AudioBuffer

  - by jfalexvijay

  I am trying to do the record using AudioUnit for iPhone app. Changes: (start) I have added the following code bufferList = (AudioBufferList *)malloc(sizeof(AudioBuffer)); bufferList-mNumberBuffers = 1; bufferList-mBuffers[0].mNumberChannels = 2; bufferList-mBuffers[0].mDataByteSize = 1024; bufferList-mBuffers[0].mData = calloc(256, sizeof(uint32_t)); Changes: (end) static OSStatus recordingCallback(void *inRefCon, AudioUnitRenderActionFlags *ioActionFlags, const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList *ioData) { OSStatus status; status = AudioUnitRender(appdelegate-audioUnit, ioActionFlags, inTimeStamp, inBusNumber, inNumberFrames, appdelegate-bufferList); if(status != 0) NSLog(@"AudioUnitRender status is %d", status); SInt16* samples = (SInt16*)(ioData-mBuffers[0].mData); ..... } fixed: (I am getting OSStatus -50 error code)- Because I didn't initialize the bufferList. I am EXC_BAD_ACCESS from AudioBuffer (ioData-mBuffers[0].mData). I am not sure with this error. Please help me to resolve it.

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• How to default-initialize local variables of built-in types in C++?

  - by sharptooth

  How do I default-initialize a local variable of primitive type in C++? For example if a have a typedef: typedef unsigned char boolean;//that's Microsoft RPC runtime typedef I'd like to change the following line: boolean variable = 0; //initialize to some value to ensure reproduceable behavior retrieveValue( &variable ); // do actual job into something that would automagically default-initialize the variable - I don't need to assign a specific value to it, but instead I only need it to be intialized to the same value each time the program runs - the same stuff as with a constructor initializer list where I can have: struct Struct { int Value; Struct() : Value() {} }; and the Struct::Value will be default-initialized to the same value every time an instance is cinstructed, but I never write the actual value in the code. How can I get the same behavior for local variables?

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• How to generate random strings that match a given regexp?

  - by Pies

  Duplicate: Random string that matches a regexp No, it isn't. I'm looking for an easy and universal method, one that I could actually implement. That's far more difficult than randomly generating passwords. I want to create an application that takes a regular expression, and shows 10 randomly generated strings that match that expression. It's supposed to help people better understand their regexps, and to decide i.e. if they're secure enough for validation purposes. Does anyone know of an easy way to do that? One obvious solution would be to write (or steal) a regexp parser, but that seems really over my head. I repeat, I'm looking for an easy and universal way to do that. Edit: Brute force approach is out of the question. Assuming the random strings would just be [a-z0-9]{10} and 1 million iterations per second, it would take 65 years to iterate trough the space of all 10-char strings.

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• C# (ASP.Net) Linking selection values to constants in Codebehind

  - by jasonvogel

  ASPX Code <asp:RadioButtonList ID="rbServer" runat="server" > <asp:ListItem Value=<%=ServerDeveloper%>> Developer </asp:ListItemv <asp:ListItem Value="dev.ahsvendor.com"> dev.test.com</asp:ListItem> <asp:ListItem Value="staging.ahsvendor.com"> staging.test.com</asp:ListItem> </asp:RadioButtonList> ASPX.CS - Codebehind const string ServerDeveloper = "developer"; ASPX Error: Code blocks are not supported in this context. Question: So what is the correct way to tie an dropdown/radio buttion/... ASPX value to a constant that is shared with the CodeBehind code? I know that I could do rbServer.Add.Item("developer") [from the CodeBehind], but is there a way to achieve it from the Presentation side of things?

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• When is C++ covariance the best solution?

  - by Neil Butterworth

  This question was asked here a few hours ago and made me realise that I have never actually used covariant return types in my own code. For those not sure what covariance is, it's allowing the return type of (typically) virtual functions to differ provided the types are part of the same inheritance hierarchy. For example: struct A { virtual ~A(); virtual A * f(); ... }; struct B : public A { virtual B * f(); ... }; The different return types of the two f() functions are said to be covariant. Older versions of C++ required the return types to be the same, so B would have to look like: struct B : public A { virtual A * f(); ... }; So, my question: Does anyone have a real-world example where covariant return types of virtual functions are required, or produce a superior solution to simply returning a base pointer or reference?

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• How to create an image from canvas data?

  - by Jakub Hampl

  In my application I am trying to save an arbitrary part of a rendered HTML canvas to an image file. In my Javascript I call ctx.getImageData(x, y, w, h) and pass the resulting object to my macruby code (though if you know a solution in objc I am also very interested). There I'm trying to create a NSBitmapImageRep object so that I can then save to an image format the user desires. This is my code so far (the function gets a WebScriptObject as it's argument): def setimagedata(d) w = d.valueForKey("width").to_i h = d.valueForKey("height").to_i data = Pointer.new(:char, d.valueForKey("data").valueForKey("length").to_i) d.valueForKey("data").valueForKey("length").to_i.times do |i| data[i] = d.valueForKey("data").webScriptValueAtIndex(i).to_i end puts "data complete" # get's called @exported_image = NSBitmapImageRep.alloc.initWithBitmapDataPlanes(data, pixelsWide: w, pixelsHigh:h, bitsPerSample: 32, samplesPerPixel: 4, hasAlpha: true, isPlanar: false, colorSpaceName: NSCalibratedRGBColorSpace, bitmapFormat: NSAlphaNonpremultipliedBitmapFormat, bytesPerRow: 0, bitsPerPixel: 0) puts "done" # doesn't get called end The code doesn't seem to get through the initWithBitmapDataPlanes function but gives no error. My question is: what am I doing wrong? Is this approach reasonable (if not, what would be better?).

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• C++'s unordered_map / hash_map / Google's dense_hash - how to input binary data (buf+len) and insert

  - by shlomif

  Hi all, I have two questions about Google's dense_hash_map, which can be used instead of the more standard unordered_map or hash_map: How do I use an arbitrary binary data memory segment as a key: I want a buffer+length pair, which may still contain some NUL (\0) characters. I can see how I use a NUL-terminated char * string , but that's not what I want. How do I implement an operation where I look if a key exists, and if not - insert it and if it does return the pointer to the existing key and let me know what actually happened. I'd appreciate it if anyone can shed any light on this subject. Regards, -- Shlomi Fish

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• Fastest algorithm to check if a number is pandigital?

  - by medopal

  Pandigital number is a number that contains the digits 1..number length. For example 123, 4312 and 967412385. I have solved many Project Euler problems, but the Pandigital problems always exceed the one minute rule. This is my pandigital function: private boolean isPandigital(int n){ Set<Character> set= new TreeSet<Character>(); String string = n+""; for (char c:string.toCharArray()){ if (c=='0') return false; set.add(c); } return set.size()==string.length(); } Create your own function and test it with this method int pans=0; for (int i=123456789;i<=123987654;i++){ if (isPandigital(i)){ pans++; } } Using this loop, you should get 720 pandigital numbers. My average time was 500 millisecond. I'm using Java, but the question is open to any language.

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• Is it possible to establish default values for inherited fields in subclasses?

  - by Christian Mann

  I'm trying to establish a default value for inherited fields from superclasses. So, my class hierarchy is thus: Character - Enemy - Boss                 \                   - Hero Each Character has a public static char avatar to represent him on an ASCII playing field. How do I set a default value for the avatar of each class inherited from Character? Thank you!

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• using arrays to get best memory alignment and cache use, is it necessary?

  - by Alberto Toglia

  I'm all about performance these days cause I'm developing my first game engine. I'm no c++ expert but after some research I discovered the importance of the cache and the memory alignment. Basically what I found is that it is recommended to have memory well aligned specially if you need to access them together, for example in a loop. Now, In my project I'm doing my Game Object Manager, and I was thinking to have an array of GameObjects references. meaning I would have the actual memory of my objects one after the other. static const size_t MaxNumberGameObjects = 20; GameObject mGameObjects[MaxNumberGameObjects]; But, as I will be having a list of components per object -Component based design- (Mesh, RigidBody, Transformation, etc), will I be gaining something with the array at all? Anyway, I have seen some people just using a simple std::map for storing game objects. So what do you guys think? Am I better off using a pure component model?

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• Why would you precede the main() function in C with a data type?

  - by Milktrader

  Many are familiar with the hello world program in C #include <stdio.h> main () { printf ("hello world"); return 0; } Why do some precede the main () function with int as in: int main() Also, I've seen the word 'void' entered inside the () as in: int main(void) It seems like extra typing for nothing, but maybe it's a best practice that pays dividends in other situations? Also, why precede main() with an int if you're returning a character string? If anything, one would expect: char main(void) I'm also foggy about why we return 0 at the end of the function.

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