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• Read a specific range of lines from a file using c

  - by James Joy

  I have the following content in a file: hhasfghgsafjgfhgfhjf gashghfdgdfhgfhjasgfgfhsgfjdg jfshafghgfgfhfsghfgffsjgfj . . . . . startread hajshjsfhajfhjkashfjf hasjgfhgHGASFHGSHF hsafghfsaghgf . . . . . stopread . . . . . . jsfjhfhjgfsjhfgjhsajhdsa jhasjhsdabjhsagshaasgjasdhjk jkdsdsahghjdashjsfahjfsd I need to read the lines from the next line of startread till the previous line of stopread using a c code and store it to a string variable(of course with a \n for every line breaks). How can i achieve this? I have used fgets(line,sizeof(line),file); but it starts reading from the beginning. I don't have the exact line number to start and stop reading since the file is written by another C code. But there are these identifiers startread and stopread to identify whereto start reading. Operating platform is linux. Thanks in advance.

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• Declaration, allocation and assignment of an array of pointers to function pointers

  - by manneorama

  Hello Stack Overflow! This is my first post, so please be gentle. I've been playing around with C from time to time in the past. Now I've gotten to the point where I've started a real project (a 2D graphics engine using SDL, but that's irrelevant for the question), to be able to say that I have some real C experience. Yesterday, while working on the event system, I ran into a problem which I couldn't solve. There's this typedef, //the void parameter is really an SDL_Event*. //but that is irrelevant for this question. typedef void (*event_callback)(void); which specifies the signature of a function to be called on engine events. I want to be able to support multiple event_callbacks, so an array of these callbacks would be an idea, but do not want to limit the amount of callbacks, so I need some sort of dynamic allocation. This is where the problem arose. My first attempt went like this: //initial size of callback vector static const int initial_vecsize = 32; //our event callback vector static event_callback* vec = 0; //size static unsigned int vecsize = 0; void register_event_callback(event_callback func) { if (!vec) __engine_allocate_vec(vec); vec[vecsize++] = func; //error here! } static void __engine_allocate_vec(engine_callback* vec) { vec = (engine_callback*) malloc(sizeof(engine_callback*) * initial_vecsize); } First of all, I have omitted some error checking as well as the code that reallocates the callback vector when the number of callbacks exceed the vector size. However, when I run this code, the program crashes as described in the code. I'm guessing segmentation fault but I can't be sure since no output is given. I'm also guessing that the error comes from a somewhat flawed understanding on how to declare and allocate an array of pointers to function pointers. Please Stack Overflow, guide me.

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• Expand chaining hashtable. Errors on code.

  - by FILIaS

  Expanding a hashtable with linked lists there are some errors and warnings. I wanna make sure that the following code is right (expand method) and find out what happens that raise these warnings/errors typedef struct { int length; struct List *head; struct List *tail; } HashTable; //resolving collisions using linked lists - chaining typedef struct { char *number; char *name; int time; struct List *next; }List; //on the insert method i wanna check hashtable's size, //if it seems appropriate there is the following code: //Note: hashtable variable is: Hashtable * ...... hashtable = expand(hashtable,number,name,time); /**WARNING**:assignment makes pointer from integer without a cast*/ HashTable* expand( HashTable* h ,char number[10],char* name,int time) /**error**: conflicting types for ‘expand’ previous implicit declaration of ‘expand’ was here*/ { HashTable* new; int n; clientsList *node,*next; PrimesIndex++; int new_size= primes[PrimesIndex]; /* double the size,odd length */ if (!(new=malloc((sizeof( List*))*new_size))) return NULL; for(n=0; n< h->length; ++n) { for(node=h[n].head; node; node=next) { add (&new, node->number, node->name,node->time); next=node->next;//// free(node); } } free(h); return new; }

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• Hi I am facing a fragmentation error while executing this code? Can someone explain why?

  - by aks

  #include<stdio.h> struct table { char *ipAddress; char *domainName; struct table *next; }; struct table *head = NULL; void add_rec(); void show_rec(); int main() { add_rec(); show_rec(); return 0; } void add_rec() { struct table * temp = head; struct table * temp1 = (struct table *)malloc(sizeof(struct table)); if(!temp1) printf("\n Unable to allocate memory \n"); printf("Enter the ip address you want \n"); scanf("%s",temp1->ipAddress); printf("\nEnter the domain name you want \n"); scanf("%s",temp1->domainName); if(!temp) { head = temp; } else { while(temp->next!=NULL) temp = temp->next; temp->next = temp1; } } void show_rec() { struct table * temp = head; if(!temp) printf("\n No entry exists \n"); while(temp!=NULL) { printf("ipAddress = %s\t domainName = %s\n",temp->ipAddress,temp->domainName); temp = temp->next; } } When i execute this code and enters the IP address for the first node, i am facing fragmentation error. The code crashed. Can someone enlighten?

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• Problem in using a second call to send() in C

  - by Paulo Victor

  Hello. Right now I'm working in a simple Server that receives from client a code referring to a certain operation. The server receives this data and send back the signal that it's waiting for the proper data. /*Server Side*/ if (codigoOperacao == 0) { printf("A escolha foi 0\n"); int bytesSent = SOCKET_ERROR; char sendBuff[1080] = "0"; /*Here "send" returns an error msgm while trying to send back the signal*/ bytesSent = send(socketEscuta, sendBuff, 1080, 0); if (bytesSent == SOCKET_ERROR) { printf("Erro ao enviar"); return 0; } else { printf("Bytes enviados : %d\n", bytesSent); char structDesmontada[1080] = ""; bytesRecv = recebeMensagem(socketEscuta, structDesmontada); printf("structDesmontada : %s", structDesmontada); } } Following here is the client code responsible for sending the operation code and receiving the signal char sendMsg[1080] = "0"; char recvMsg[1080] = ""; bytesSent = send(socketCliente, sendMsg, sizeof(sendMsg), 0); printf("Enviei o codigo (%d)\n", bytesSent); /*Here the program blocks in a infinite loop since the server never send anything*/ while (bytesRecv == SOCKET_ERROR) { bytesRecv = recv(socketCliente, recvMsg, 1080, 0); if (bytesRecv > 0) { printf("Recebeu\n"); } Why this is happening only in the second attempt to send some data? Because the first call to send() works fine. Hope someone can help!! Thnks

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• Is there a good way to copy a Gtk widget?

  - by Jake

  Is there a way, using the Gtk library in C, to clone a Gtk button (for instance), and pack it somewhere else in the app. I know you can't pack the same widget twice. And that this code obviously wouldn't work, but shows what happens when I attempt a shallow copy of the button: GtkButton *a = g_object_new(GTK_TYPE_BUTTON, "label", "o_0", NULL); GtkButton *b = g_memdup(b, sizeof *b); gtk_box_pack_start_defaults(GTK_BOX(vbox), GTK_WIDGET(b)); There is surrounding code which creates a vbox and packs it in a window and runs gtk_main(). This will result in these hard to understand error messages: (main:6044): Gtk-CRITICAL **: gtk_widget_hide: assertion `GTK_IS_WIDGET (widget)' failed (main:6044): Gtk-CRITICAL **: gtk_widget_realize: assertion `GTK_WIDGET_ANCHORED (widget) || GTK_IS_INVISIBLE (widget)' failed ** Gtk:ERROR:/build/buildd/gtk+2.0-2.18.3/gtk/gtkwidget.c:8431:gtk_widget_real_map: assertion failed: (GTK_WIDGET_REALIZED (widget)) Along the same lines, if I were to write my own GObject (not necessarily a Gtk widget), is there a good way to write a copy constructor. Im thinking it should be an interface with optional hooks and based mostly on the properties, handling the class's hierarchy in some way. I'd want to do this: GtkButton *b = copyable_copy(COPYABLE(a)); If GtkButton could use a theoretical copyable interface.

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• PHP Preg_replace after a specific amount of characters with a conditional

  - by Marc Ripley

  I've been working on this for a bit, but my regex is weak. I need to check to see if a number is a whole number (single digit) and append a ".001" to it if so. The problem is, it's in the middle of a line with values separated by commas. MATERIALS,1,1,9999;1 4PL1 PB_Mel,,1,6,0.173,0.173,0.375,0,0.375,0,0,0,0,2,0,1,1 Needs to be MATERIALS,1,1,9999;1 4PL1 PB_Mel,,1.001,6,0.173,0.173,0.375,0,0.375,0,0,0,0,2,0,1,1 The line must start with "MATERIALS". There are more than one MATERIALS lines. The value will always be after 5 commas. I was trying something like this to even replace the number, but I don't think the approach is quite right: $stripped = preg_replace('/(MATERIALS)(,.*?){4}(,\d+?),/', '\2,', $stripped); I tried going through a preg_match_all for if process, to at least get the conditional working, but I still have to replace the lines. for($i=0;$i<sizeof($materialsLines[0]);$i++) { $section = explode(",",$materialsLines[0][$i]); if (strlen($section[5]) == 1) { $section[5] .= ".001"; } $materialsLines[0][$i] = implode(",",$section); }

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• JNI Stream binary data from C++ to Java

  - by Cliff

  I need help passing binary data into Java. I'm trying to use jbytearray but when the data gets into Java it appears corrupt. Can somebody give me a hand? Here's a snip of some example code. First the native C++ side: printf("Building audio array copy\n"); jbyteArray rawAudioCopy = env-NewByteArray(10); jbyte toCopy[10]; printf("Filling audio array copy\n"); char theBytes[10] = {0,1,2,3,4,5,6,7,8,9}; for (int i = 0; i < sizeof(theBytes); i++) { toCopy[i] = theBytes[i]; } env->SetByteArrayRegion(rawAudioCopy,0,10,toCopy); printf("Finding object callback\n"); jmethodID aMethodId = env->GetMethodID(env->GetObjectClass(obj),"handleAudio","([B)V"); if(0==aMethodId) throw MyRuntimeException("Method not found error",99); printf("Invoking the callback\n"); env->CallVoidMethod(obj,aMethodId, &rawAudioCopy); and then the Java callback method: public void handleAudio(byte[] audio){ System.out.println("Audio supplied to Java [" + audio.length + "] bytes"); byte[] expectedAudio = {0,1,2,3,4,5,6,7,8,9}; for (int i = 0; i < audio.length; i++) { if(audio[i]!= expectedAudio[i]) System.err.println("Expected byte " + expectedAudio[i] + " at byte " + i + " but got byte " + audio[i]); else System.out.print('.'); } System.out.println("Audio passed back accordingly!"); } I get the following output when the callback is invoked: library loaded! Audio supplied to Java [-2019659176] bytes Audio passed back accordingly!

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• How can I render an in-memory UIViewController's view Landscape?

  - by Aaron

  I'm trying to render an in-memory (but not in hierarchy, yet) UIViewController's view into an in-memory image buffer so I can do some interesting transition animations. However, when I render the UIViewController's view into that buffer, it is always rendering as though the controller is in Portrait orientation, no matter the orientation of the rest of the app. How do I clue this controller in? My code in RootViewController looks like this: MyUIViewController* controller = [[MyUIViewController alloc] init]; int width = self.view.frame.size.width; int height = self.view.frame.size.height; int bitmapBytesPerRow = width * 4; unsigned char *offscreenData = calloc(bitmapBytesPerRow * height, sizeof(unsigned char)); CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); CGContextRef offscreenContext = CGBitmapContextCreate(offscreenData, width, height, 8, bitmapBytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast); CGContextTranslateCTM(offscreenContext, 0.0f, height); CGContextScaleCTM(offscreenContext, 1.0f, -1.0f); [(CALayer*)[controller.view layer] renderInContext:offscreenContext]; At that point, the offscreen memory buffers contents are portrait-oriented, even when the window is in landscape orientation. Ideas?

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• C++: static assert for const variables?

  - by shoosh

  Static asserts are very convenient for checking things in compile time. A simple static assert idiom looks like this: template<bool> struct StaticAssert; template<> struct StaticAssert<true> {}; #define STATIC_ASSERT(condition) do { StaticAssert<condition>(); } while(0) This is good for stuff like STATIC_ASSERT(sizeof(float) == 4) and: #define THIS_LIMIT (1000) ... STATIC_ASSERT(THIS_LIMIT > OTHER_LIMIT); But using #define is not the "C++" way of defining constants. C++ would have you use an anonymous namespace: namespace { const int THIS_LIMIT = 1000; } or even: static const int THIS_LIMIT = 1000; The trouble with this is that with a const int you can't use STATIC_ASSERT() and you must resort to a run-time check which is silly. Is there a way to properly solve this in current C++? I think I've read C++0x has some facility to do this...

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• pthread_exit and/or pthread_join causing Abort and SegFaults.

  - by MJewkes

  The following code is a simple thread game, that switches between threads causing the timer to decrease. It works fine for 3 threads, causes and Abort(core dumped) for 4 threads, and causes a seg fault for 5 or more threads. Anyone have any idea why this might be happening? #include <stdio.h> #include <stdlib.h> #include <pthread.h> #include <errno.h> #include <assert.h> int volatile num_of_threads; int volatile time_per_round; int volatile time_left; int volatile turn_id; int volatile thread_running; int volatile can_check; void * player (void * id_in){ int id= (int)id_in; while(1){ if(can_check){ if (time_left<=0){ break; } can_check=0; if(thread_running){ if(turn_id==id-1){ turn_id=random()%num_of_threads; time_left--; } } can_check=1; } } pthread_exit(NULL); } int main(int argc, char *args[]){ int i; int buffer; pthread_t * threads =(pthread_t *)malloc(num_of_threads*sizeof(pthread_t)); thread_running=0; num_of_threads=atoi(args[1]); can_check=0; time_per_round = atoi(args[2]); time_left=time_per_round; srandom(time(NULL)); //Create Threads for (i=0;i<num_of_threads;i++){ do{ buffer=pthread_create(&threads[i],NULL,player,(void *)(i+1)); }while(buffer == EAGAIN); } can_check=1; time_left=time_per_round; turn_id=random()%num_of_threads; thread_running=1; for (i=0;i<num_of_threads;i++){ assert(!pthread_join(threads[i], NULL)); } return 0; }

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• C when to allocate and free memory - before function call, after function call...etc

  - by Keith P

  I am working with my first straight C project, and it has been a while since I worked on C++ for that matter. So the whole memory management is a bit fuzzy. I have a function that I created that will validate some input. In the simple sample below, it just ignores spaces: int validate_input(const char *input_line, char* out_value){ int ret_val = 0; /*false*/ int length = strlen(input_line); cout << "length = " << length << "\n"; out_value =(char*) malloc(sizeof(char) * length + 1); if (0 != length){ int number_found = 0; for (int x = 0; x < length; x++){ if (input_line[x] != ' '){ /*ignore space*/ /*get the character*/ out_value[number_found] = input_line[x]; number_found++; /*increment counter*/ } } out_value[number_found + 1] = '\0'; ret_val = 1; } return ret_val; } Instead of allocating memory inside the function for out_value, should I do it before I call the function and always expect the caller to allocate memory before passing into the function? As a rule of thumb, should any memory allocated inside of a function be always freed before the function returns?

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• Intel MKL memory management and exceptions

  - by Andrew

  Hello everyone, I am trying out Intel MKL and it appears that they have their own memory management (C-style). They suggest using their MKL_malloc/MKL_free pairs for vectors and matrices and I do not know what is a good way to handle it. One of the reasons for that is that memory-alignment is recommended to be at least 16-byte and with these routines it is specified explicitly. I used to rely on auto_ptr and boost::smart_ptr a lot to forget about memory clean-ups. How can I write an exception-safe program with MKL memory management or should I just use regular auto_ptr's and not bother? Thanks in advance. EDIT http://software.intel.com/sites/products/documentation/hpc/mkl/win/index.htm this link may explain why I brought up the question UPDATE I used an idea from the answer below for allocator. This is what I have now: template <typename T, size_t TALIGN=16, size_t TBLOCK=4> class aligned_allocator : public std::allocator<T> { public: pointer allocate(size_type n, const void *hint) { pointer p = NULL; size_t count = sizeof(T) * n; size_t count_left = count % TBLOCK; if( count_left != 0 ) count += TBLOCK - count_left; if ( !hint ) p = reinterpret_cast<pointer>(MKL_malloc (count,TALIGN)); else p = reinterpret_cast<pointer>(MKL_realloc((void*)hint,count,TALIGN)); return p; } void deallocate(pointer p, size_type n){ MKL_free(p); } }; If anybody has any suggestions, feel free to make it better.

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• How do I create an inheritable Semaphore in .NET?

  - by pauldoo

  I am trying to create a Win32 Semaphore object which is inheritable. This means that any child processes I launch may automatically have the right to act on the same Win32 object. My code currently looks as follows: Semaphore semaphore = new Semaphore(0, 10); Process process = Process.Start(pathToExecutable, arguments); But the semaphore object in this code cannot be used by the child process. The code I am writing is a port of come working C++. The old C++ code achieves this by the following: SECURITY_ATTRIBUTES security = {0}; security.nLength = sizeof(security); security.bInheritHandle = TRUE; HANDLE semaphore = CreateSemaphore(&security, 0, LONG_MAX, NULL); Then later when CreateProcess is called the bInheritHandles argument is set to TRUE. (In both the C# and C++ case I am using the same child process (which is C++). It takes the semaphore ID on command line, and uses the value directly in a call to ReleaseSemaphore.) I suspect I need to construct a special SemaphoreSecurity or ProcessStartInfo object, but I haven't figured it out yet.

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• java: "downcasting" to new object / opposite of slicing

  - by rhavin

  Sorry, i really dont know how to make a headline for that question; maybe there is a name for what im trying to do that i dont know, but i can explain it with some code: Guess you have a class that unfortunately neither has a copy-constructor nor a public static copy method. class A { private int i; // <- private, cant access String x; // <- even worse: cant access unless in same pkg! /* … other stuff, ctor, etc. … */ public A clone() { A a = new A(); a.i = i; a.x = x; return x; } } Guess further, there is some function that returns an object of that class: public static A someFn(x,y,z); Now the problem: I want to derive from that class to add some functionality. Unfortunately, i neither have a sizeof in java nor a cc or static copy method. So when i do a class B extends A { protected w; public B clone() { /* as usual */ } } then i can clone my B and get a new one, but how can i convert the returned A from someFn() into a B. Is there anyway to do the opposite of slicing in java? if i clone it, it's still an A, and i cant copy it field by field. This is all simple in c++, but how to do this in Java?

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• C : files manipulation Can't figure out how to simplify this code with files manipulation.

  - by Bon_chan

  Hey guys, I have been working on this code but I can't find out what is wrong. This program does compile and run but it ends up having a fatal error. I have a file called myFile.txt, with the following content : James------ 07.50 Anthony--- 17.00 And here is the code : int main() { int n =2, valueTest=0,count=0; FILE* file = NULL; float temp= 00.00f, average= 00.00f, flTen = 10.00f; float *totalNote = (float*)malloc(n*sizeof(float)); int position = 0; char selectionNote[5+1], nameBuffer[10+1], noteBuffer[5+1]; file = fopen("c:\\myFile.txt","r"); fseek(file,10,SEEK_SET); while(valueTest<2) { fscanf(file,"%5s",&selectionNote); temp = atof(selectionNote); totalNote[position]= temp; position++; valeurTest++; } for(int counter=0;counter<2;counter++) { average += totalNote[counter]; } printf("The total is : %f \n",average); rewind(file); printf("here is the one with less than 10.00 :\n"); while(count<2) { fscanf(file,"%10s",&nameBuffer); fseek(file,10,SEEK_SET); fscanf(file,"%5s",&noteBuffer); temp = atof(noteBuffer); if(temp<flTen) { printf("%s who has %f\n",nameBuffer,temp); } fseek(file,1,SEEK_SET); count++; } fclose(file); } I am pretty new to c and find it more difficult than c# or java. And I woud like to get some suggestions to help me to get better. I think this code could be simplier. Do you think the same ?

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• Reading a C/C++ data structure in C# from a byte array

  - by Chris Miller

  What would be the best way to fill a C# struct from a byte[] array where the data was from a C/C++ struct? The C struct would look something like this (my C is very rusty): typedef OldStuff { CHAR Name[8]; UInt32 User; CHAR Location[8]; UInt32 TimeStamp; UInt32 Sequence; CHAR Tracking[16]; CHAR Filler[12];} And would fill something like this: [StructLayout(LayoutKind.Explicit, Size = 56, Pack = 1)]public struct NewStuff{ [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)] [FieldOffset(0)] public string Name; [MarshalAs(UnmanagedType.U4)] [FieldOffset(8)] public uint User; [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 8)] [FieldOffset(12)] public string Location; [MarshalAs(UnmanagedType.U4)] [FieldOffset(20)] public uint TimeStamp; [MarshalAs(UnmanagedType.U4)] [FieldOffset(24)] public uint Sequence; [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 16)] [FieldOffset(28)] public string Tracking;} What is best way to copy OldStuff to NewStuff, if OldStuff was passed as byte[] array? I'm currently doing something like the following, but it feels kind of clunky. GCHandle handle;NewStuff MyStuff;int BufferSize = Marshal.SizeOf(typeof(NewStuff));byte[] buff = new byte[BufferSize];Array.Copy(SomeByteArray, 0, buff, 0, BufferSize);handle = GCHandle.Alloc(buff, GCHandleType.Pinned);MyStuff = (NewStuff)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(NewStuff));handle.Free(); Is there better way to accomplish this?

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• object / class methods serialized as well?

  - by Mat90

  I know that data members are saved to disk but I was wondering whether object's/class' methods are saved in binary format as well? Because I found some contradictionary info, for example: Ivor Horton: "Class objects contain function members as well as data members, and all the members, both data and functions, have access specifiers; therefore, to record objects in an external file, the information written to the file must contain complete specifications of all the class structures involved." and: Are methods also serialized along with the data members in .NET? Thus: are method's assembly instructions (opcodes and operands) stored to disk as well? Just like a precompiled LIB or DLL? During the DOS ages I used assembly so now and then. As far as I remember from Delphi and the following site (answer by dan04): Are methods also serialized along with the data members in .NET? sizeof(<OBJECT or CLASS>) will give the size of all data members together (no methods/procedures). Also a nice C example is given there with data and members declared in one class/struct but at runtime these methods are separate procedures acting on a struct of data. However, I think that later class/object implementations like Pascal's VMT may be different in memory.

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• How can I modified the value of a string defined in a struc?

  - by Eric

  Hi, I have the following code in c++: define TAM 4000 define NUMPAGS 512 struct pagina { bitset<12 direccion; char operacion; char permiso; string *dato; int numero; }; void crearPagina(pagina* pag[], int pos, int dir) { pagina * paginas = (pagina*)malloc(sizeof(char) * TAM); paginas - direccion = bitset<12 (dir); paginas - operacion = 'n'; paginas - permiso = 'n'; string **tempDato = &paginas - dato; char *temp = " "; **tempDato = temp; paginas - numero = 0; pag[pos] = paginas; } I want to modify the value of the variable called "string *dato" in the struct pagina but, everytime I want to assing a new value, the compiler throws a segmentation fault. In this case I'm using a pointer to string, but I have also tried with a string. In a few words I want to do the following: pagina - dato = "test"; Any idea? Thanks in advance!!!

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• Delphi fast large bitmap creation (without clearing)

  - by Ritsaert Hornstra

  When using the TBitmap wrapper for a GDI bitmap from the unit Graphics I noticed it will always clear out the bitmap (using a PatBlt call) when setting up a bitmap with SetSize( w, h ). When I copy in the bits later on (see routine below) it seems ScanLine is the fastest possibility and not SetDIBits. function ToBitmap: TBitmap; var i, N, x: Integer; S, D: PAnsiChar; begin Result := TBitmap.Create(); Result.PixelFormat := pf32bit; Result.SetSize( width, height ); S := Src; D := Result.ScanLine[ 0 ]; x := Integer( Result.ScanLine[ 1 ] ) - Integer( D ); N := width * sizeof( longword ); for i := 0 to height - 1 do begin Move( S^, D^, N ); Inc( S, N ); Inc( D, x ); end; end; The bitmaps I need to work with are quite large (150MB of RGB memory). With these iomages it takes 150ms to simply create an empty bitmap and a further 140ms to overwrite it's contents. Is there a way of initializing a TBitmap with the correct size WITHOUT initializing the pixels itself and leaving the memory of the pixels uninitialized (eg dirty)? Or is there another way to do such a thing. I know we could work on the pixels in place but this still leaves the 150ms of unnessesary initializtion of the pixels.

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• error in C++, what to do ?: could not find an match for ostream::write(long *, unsigned int)

  - by Shantanu Gupta

  I am trying to write data stored in a binary file using turbo C++. But it shows me an error could not find an match for ostream::write(long *, unsigned int) I want to write a 4 byte long data into that file. When i tries to write data using char pointer. It runs successfully. But i want to store large value i.e. eg. 2454545454 Which can be stored in long only. I dont know how to convert 1 byte into bit. I have 1 byte of data as a character. Moreover what i m trying to do is to convert 4 chars into long and store data into it. And at the other side i want to reverse this so as to retrieve how many bytes of data i have written. long *lmem; lmem=new long; *lmem=Tsize; fo.write(lmem,sizeof(long));// error occurs here delete lmem; I am implementing steganography and i have successfully stored txt file into image but trying to retrieve that file data now.

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• What happens to class members when malloc is used instead of new?

  - by Felix

  I'm studying for a final exam and I stumbled upon a curious question that was part of the exam our teacher gave last year to some poor souls. The question goes something like this: Is the following program correct, or not? If it is, write down what the program outputs. If it's not, write down why. The program: #include<iostream.h> class cls { int x; public: cls() { x=23; } int get_x(){ return x; } }; int main() { cls *p1, *p2; p1=new cls; p2=(cls*)malloc(sizeof(cls)); int x=p1->get_x()+p2->get_x(); cout<<x; return 0; } My first instinct was to answer with "the program is not correct, as new should be used instead of malloc". However, after compiling the program and seeing it output 23 I realize that that answer might not be correct. The problem is that I was expecting p2->get_x() to return some arbitrary number (whatever happened to be in that spot of the memory when malloc was called). However, it returned 0. I'm not sure whether this is a coincidence or if class members are initialized with 0 when it is malloc-ed. Is this behavior (p2->x being 0 after malloc) the default? Should I have expected this? What would your answer to my teacher's question be? (besides forgetting to #include <stdlib.h> for malloc :P)

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• Modify existing struct alignment in Visual C++

  - by Crend King

  Is there a way to modify the member alignment of an existing struct in Visual C++? Here is the background: I use an 3rd-party library, which uses several structs. To fill up the structs, I pass the address of the struct instance to some functions. Unfortunately, the functions only returns unaligned buffer, so that data of some members are always wrong. /Zp is out of choice, since it breaks the other parts of the program. I know #pragma pack modifies the alignment of the following struct, but I do not want to copy the structs into my code, for the definitions in the library might change in the future. Sample code: test.h: struct am_aligned { BYTE data1[10]; ULONG data2; }; test.cpp: include "test.h" // typedef alignment(1) struct am_aligned am_unaligned int APIENTRY wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow) { char buffer[20] = {}; for (int i = 0; i < sizeof(unaligned_struct); i++) { buffer[i] = i; } am_aligned instance = *(am_aligned*) buffer; return 0; } instance.data2 is 0x0f0e0d0c, while 0x0d0c0b0a is desired. The commented line does not work of course. Thanks for help!

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• How to store an interger value of 4 bytes in a memory of chunk which is malloced as type char

  - by Adi

  Dear all, Hello Guys!! This is my first post in the forum . I am really looking forward to having good fun in this site. My question is : int mem_size = 10; char *start_ptr; if((start_ptr= malloc(mem_size*1024*1024*sizeof(char)))==NULL) {return -1;} I have allocated a chunk of memory of type char and size is say 10 MB (i.e mem_size = 10 ); Now I want to store the size information in the header of the memory chunk, To make myself more clear Lets Say : start_ptr = 0xaf868004 (This is the value I got from my execution, it changes every time) Now I want to put the size information in the start of this pointer.. i.e *start_ptr = mem_size*1024*1024; But I am not able to put this information in the start_ptr. I think the reason is because my ptr is of type char which only takes one byte but I am trying to store int which takes 4 bytes, is the problem . I am not sure how to fix this problem.. I would greatly appreciate your suggestions. Cheers!! Aditya

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• Pointer arithmetic.

  - by Knowing me knowing you

  Having code: int** a = new int*[2]; a[0] = new int(1); a[1] = new int(2); cout << "a[0] " << a[0] << '\n'; cout << "a[1] " << a[1] << '\n'; cout << "a[2] " << a[2] << '\n'; cout << "a[0] + 1 " << a[0] + 1 << '\n';//WHY THIS ISN'T == a[1] ? cout << "*(a + 1): " << *(a + 1) << '\n'; //WHY THIS IS == a[1] ? cout << "a[0] - a[1] " << static_cast<int>(a[0] - a[1])<< '\n';//WHY THIS IS == 16 not 4? cout << sizeof(int**); Questions are included right next to relevant lines in code.

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