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• ctypes and pointer manipulation

  - by Chris

  I am dealing with image buffers, and I want to be able to access data a few lines into my image for analysis with a c library. I have created my 8-bit pixel buffer in Python using create_string_buffer. Is there a way to get a pointer to a location within that buffer without re-creating a new buffer? My goal is to analyze and change data within that buffer in chunks, without having to do a lot of buffer creation and data copying. In this case, ultimately, the C library is doing all the manipulation of the buffer, so I don't actually have to change values within the buffer using Python. I just need to give my C function access to data within the buffer.

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• Access violation of member of pointer object

  - by Martin Lauridsen

  So I am coding this client/server program. This code is from the client side. The client has an instance of an object mpqs_sieve *instance_; The reason I make it as a pointer is, that mpqs_sieve only has a constructor that takes 3 arguments, and I want to instantiate it at a later point in time. The client first gets some data from the server, and uses this to instantiate instance_. After this, it will request some more data, and upon receiving this (these are three coeffecients for a quadratic polynomial), it should set these in the instance_ object. However upon calling a member function of instance_, I get an access violation on one of the members of instance_ within that function call. I posted my code here: on pastebin, and I get the error on line 100. The call comes from line 71, and before that line 21. Any ideas to solve this? Thanks!

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• Purpose of dereferencing a pointer as a parameter in C.

  - by Leif Andersen

  I recently came along this line of code: CustomData_em_free_block(&em->vdata, &eve->data); And I thought, isn't: a->b just syntactic sugar for: (*a).b With that in mind, this line could be re-written as: CustomData_em_free_block(&(*em).vdata, &(*eve).data); If that's the case, what is the point of passing in &(*a), as a parameter, and not just a? It seems like the pointer equivalent of -(-a) is being passed in in, is there any logic for this? Thank you.

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• How to do pointer work with accessor methods in Objective-C

  - by Jasconius

  Basic problem statement: I have a very good reason for doing some pointer fanciness in an app where I need to pass a decimal by reference. So I have a class which stores many a decimal, so let's say is has a property as such: @property (nonatomic) double myDecimalValue; I want to pass it by reference to some other class. [someOtherObject sendMyDecimalByReference:&myDecimalValue]; But, a problem emerges! The way that actually has to be written (because it's a property) is [someOtherObject sendMyDecimalByReference:&decimalOrigin.myDecimalValue]; This fails to compile in objective-c I get around it by writing the following - (double *) myDecimalValueRef; [someOtherObject sendMyDecimalByReference:[decimalOrigin myDecimalValue]]; Except I have dozens of these decimals and I don't want to write that stupid wrapper function for every value. Is there a shorthand way to do this in Objective-C using just the Getter functions? Let's just assume I have a great reason for not using NSNumber. Thanks!

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• How to set the pointer to the current row in the Datagridview in C Sharp

  - by user286546

  I have a datagridview on the Windows Form in c#. I am updating and filling the table adapter on the cell event. The problem is that When I go to lower half of the datagrid which is not visible until I scroll down, as I click any cell, the table adapter is filled and updated and the pointerpoints to the very first row. Any suggestion on how to fix it. I have a ideas to record the top row of the datagridview that is visible and set the pointer to that row. But how to do it?

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• GLib Hash Table - Pointer

  - by Mike

  I'm trying to increment the value of some specific key if it was found. For some reason I keep getting the (pointer) address when I dump all keys:values from the hash table. Output a: 153654132 // should be 5 b: 1 c: 153654276 // should be 3 d: 1 e: 1 f: 153654420 // should be 3 int proc() { struct st stu; gpointer ok, ov; //... some non-related code here if(!g_hash_table_lookup_extended(ht, key, &ok, &ov)){ stu.my_int = g_malloc(sizeof(guint)); *(stu.my_int) = 0; g_hash_table_insert(table, g_strdup(key), GINT_TO_POINTER(1)); }else{ stu.my_int = g_malloc(sizeof(guint)); *(stu.my_int)++; g_hash_table_insert(table, g_strdup(key), stu.my_int); } } Any ideas will be appreciate it.

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• GLib Hash Table - Pointer

  - by Mike

  I'm trying to increment the value of some specific key if it was found. For some reason I keep getting the (pointer) address when I dump all keys:values from the hash table. Output a: 153654132 // should be 5 b: 1 c: 153654276 // should be 3 d: 1 e: 1 f: 153654420 // should be 3 int proc() { struct st stu; gpointer ok, ov; //... some non-related code here if(!g_hash_table_lookup_extended(table, key, &ok, &ov)){ stu.my_int = g_malloc(sizeof(guint)); *(stu.my_int) = 0; g_hash_table_insert(table, g_strdup(key), GINT_TO_POINTER(1)); }else{ stu.my_int = g_malloc(sizeof(guint)); *(stu.my_int)++; g_hash_table_insert(table, g_strdup(key), stu.my_int); } } Any ideas will be appreciate it.

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• Pointer initialization doubt

  - by Jestin Joy

  We could initialize a character pointer like this in C. char *c="test"; Where c points to the first character(t). But when I gave code like below. It gives segmentation fault. #include<stdio.h> #include<stdlib.h> main() { int *i=0; printf("%d",*i); } Also when I give #include<stdio.h> #include<stdlib.h> main() { int *i; i=(int *)malloc(2); printf("%d",*i); } It worked(gave output 0). When I gave malloc(0), it worked(gave output 0). Please tell what is happening

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• HTML Chrome Audit Specify Image Dimensions

  - by AKRamkumar

  I just started using the chrome developer tools for some basic html websites and I used the audit tool. I had two identical images, one with the height and width attribute, and one without. On the Resources section, both the latency and the download time were identical. However, the Audit showed Specify image dimensions (1) A width and height should be specified for all images in order to speed up page display. Does this actually help? And are there any other ways to speed up page time? This is only a splash page for the website I am building and as such it is only html, no css or javascript or anything. I have already compressed the images but I want to speed up load time even more. Is there a way?

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• Array pointer arithmetic question

  - by Konrad

  Is there a way to figure out where in an array a pointer is? Lets say we have done this: int nNums[10] = {'11','51','23', ... }; // Some random sequence int* pInt = nNums[4]; // Some index in the sequence. ... pInt++; // Assuming we have lost track of the index by this stage. ... Is there a way to determine what element index in the array pInt is 'pointing' to without walking the array again?

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• Referring to this pointer in a static assert?

  - by Tyson Jacobs

  Is it possible to write a static assert referring to the 'this' pointer? I do not have c++11 available, and BOOST_STATIC_ASSERT doesn't work. struct blah { void func() {BOOST_STATIC_ASSERT(sizeof(*this));} }; Produces: error C2355: 'this' : can only be referenced inside non-static member functions error C2027: use of undefined type 'boost::STATIC_ASSERTION_FAILURE' In MSVC 2008. Motivation: #define CLASS_USES_SMALL_POOL() \ void __small_pool_check() {BOOST_STATIC_ASSERT(sizeof(*this) < SMALL_MALLOC_SIZE;} \ void* operator new(size_t) {return SmallMalloc();} \ void operator delete(void* p) {SmallFree(p);}

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• Heap corruption detected error when attempting to free pointer

  - by AndyGeek

  Hi, I'm pretty new to C++ and have run into a problem which I have not been able to solve. I'm trying to convert a System::String to a wchar_t pointer that I can keep for longer than the scope of the function. Once I'm finished with it, I want to clean it up properly. Here is my code: static wchar_t* g_msg; int TestConvert() { pin_ptr<const wchar_t> wchptr = PtrToStringChars("Test"); g_msg = (wchar_t*)realloc(g_msg, wcslen(wchptr) + 1); wcscpy(g_msg, wchptr); free (g_msg); // Will be called from a different method } When the free is called, I'm getting "HEAP CORRUPTION DETECTED: after Normal block (#137) at 0x02198F90." Why would I be getting this error? Andrew L

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• C++ - dynamic pointer of array

  - by Eagle

  Hi to all, first i would like to say i am Newbie in C++. As part of my master thesis i am writing a program in C++ which also get as parameters the variables m and d (both integers). Were d is the power of 2 (this means 2^d elements). Parameter m define the number of possible interactions between one element and the total group (2^d elements). The number of possible interactions is computed as following: \kappa = \sum_{i=0}^m\binom{d}{i} (at present i generate vector of vectors for 2^d x \kappa, but my Prof. would like me to create different statistics to different m's. My first though was to to generate a dynamic array of m arrays of different sizes... Then i though of defining a 3-dim array with the biggest needed 2d array, but also program speed is important (e.g d = 20). i would like to ask for your advice how to define such kind of dynamic array that will also be fast. Regards

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• Paypal - DoExpressCheckoutPayment null pointer

  - by user969894

  String nvpstr = "&TOKEN=" + token + "&PAYERID=" + payerID + "&PAYMENTREQUEST_0_PAYMENTACTION=" + paymentType + "&PAYMENTREQUEST_0_AMT=" + finalPaymentAmount + "&PAYMENTREQUEST_0_CURRENCYCODE=" + currencyCodeType + "&IPADDRESS=" + serverName; Having done an earlier call to SetExpressCheckout, I had to change a few parameter names because Paypal had changed it in the documentation but not in the code from the integration wizard. Now for DoExpressCheckoutPayment I've modified a few but I get a null pointer at strAck: HashMap nvp = httpcall("DoExpressCheckoutPayment", nvpstr); String strAck = nvp.get("ACK").toString(); if (strAck.equalsIgnoreCase("Success")) { return nvp; } Not sure what is wrong, any suggestions for debugging this or possible solutions?

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• C++ smart pointer for a non-object type?

  - by Brian

  Hi, I'm trying to use smart pointers such as auto_ptr, shared_ptr. However, I don't know how to use it in this situation. CvMemStorage *storage = cvCreateMemStorage(); ... use the pointer ... cvReleaseMemStorage(&storage); I'm not sure, but I think that the storage variable is just a malloc'ed memory, not a C++ class object. Is there a way to use the smart pointers for the storage variable? Thank you.

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• C++ smart pointer for non-object type?

  - by Brian

  Hi, I'm trying to use smart pointers such as auto_ptr, shared_ptr. However, I don't know how to use it in this situation. CvMemStorage *storage = cvCreateMemStorage(); ... use the pointer ... cvReleaseMemStorage(&storage); I'm not sure, but I think that the storage variable is just malloc'ed memory, not object. Is there a way to use the smart pointers for the storage variable? Thank you.

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• How to handle JPA annotations for a pointer to a generic interface

  - by HDave

  I have a generic class that is also a mapped super class that has a private field that holds a pointer to another object of the same type: @MappedSuperclass public abstract class MyClass<T extends MyIfc<T>> implements MyIfc<T> { @OneToOne() @JoinColumn(name = "previous", nullable = true) private T previous; ... } My problem is that Eclipse is showing an error in the file at the OneToOne "Target Entity "T" for previous is not an Entity." All of the implementations of MyIfc are, in fact, Entities. I should also add that each concrete implementation that inherit from MyClass uses a different value for T (because T is itself) so I can't use the "targetEntity" attribute. I guess if there is no answer then I'll have to move this JPA annotation to all the concrete subclasses of MyClass. It just seems like JPA/Hibernate should be smart enough to know it'll all work out at run-time. Makes me wonder if I should just ignore this error somehow.

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• Comparison between pointer and integer (cocoa)

  - by Cal S

  Hi, I'm just learning cocoa (coming from C#) but I'm getting a strange error for something that seems really simple... (charsSinceLastUpdate=36) #import "CSMainController.h" @implementation CSMainController //global vars int *charsSinceLastUpdate = 0; NSString *myString = @"Hello world"; // - (void)applicationDidFinishLaunching:(NSNotification *)aNotification { ... } //other functions - (void)textDidChange:(NSNotification *)aNotification { NSLog(@"charsSinceLastUpdate=%i",charsSinceLastUpdate); if (charsSinceLastUpdate>=36) { // <- THIS line returns the error: Comparison between pointer and integer charsSinceLastUpdate=0; [statusText setStringValue:@"Will save now!"]; } else { charsSinceLastUpdate++; [statusText setStringValue:@"Not saving"]; } } //my functions - (void)showNetworkErrorAlert:(BOOL)showContinueWithoutSavingOption { ... } // @end Any help would be appreciated, thanks!

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• Forked Function not assigning pointer

  - by Luke Mcneice

  In the code below I have a function int GetTempString(char Query[]); calling it in main works fine. However, when calling the function from a fork the fork hangs (stops running, no errors, no output) before this line: pch = strtok (Query," ,"); the printf shows that the pointer to pch is null. Again this only happens when the fork is executing it. What am I doing doing wrong? int main() { if((Timer =fork())==-1) printf("Timer Fork Failed"); else if(Timer==0) { while(1) { sleep(2); GetTempString("ch 1,2,3,4"); } } else { //CODE GetTempString("ch 1,2,3,4"); } } int GetTempString(char Query[]) { char * pch; printf("DEBUG: '%s'-'%d'\n",Query,pch); pch = strtok (Query," ,");//* PROBLEM HERE* //while loop for strtok... return 1; }

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• storing an integral value in a pointer variable while declaration

  - by benjamin button

  int main() { int *d=0; printf("%d\n",*d); return 0; } this works fine. >cc legal.c > ./a.out 0 if i change the statement int *d=0; to int *d=1; i see the error. cc: "legal.c", line 6: error 1522: Cannot initialize a pointer with an integer constant other than zero. so its obvious that it will allow only zero.i want to know what happens inside the memory when we do this int *d=0 which is making it valid syntax. I am just asking this out of curiosity!

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• Dangling pointer

  - by viswanathan

  Does this piece of code lead to dangling pointer. My guess is no. class Sample { public: int *ptr; Sample(int i) { ptr = new int(i); } ~Sample() { delete ptr; } void PrintVal() { cout << "The value is " << *ptr; } }; void SomeFunc(Sample x) { cout << "Say i am in someFunc " << endl; } int main() { Sample s1 = 10; SomeFunc(s1); s1.PrintVal(); }

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• C++ run error: pointer being freed was not allocated

  - by Dale Reves

  I'm learning c++ and am working on a program that keeps giving me a 'pointer being freed was not allocated' error. It's a grocery store program that inputs data from a txt file, then user can enter item# & qty. I've read through similar questions but what's throwing me off is the 'pointer' issue. I would appreciate if someone could take a look and help me out. I'm using Netbeans IDE 7.2 on a Mac. I'll just post the whole piece I have so far. Thx. #include <iostream> #include <fstream> #include <string> #include <vector> using namespace std; class Product { public: // PLU Code int getiPluCode() { return iPluCode; } void setiPluCode( int iTempPluCode) { iPluCode = iTempPluCode; } // Description string getsDescription() { return sDescription; } void setsDescription( string sTempDescription) { sDescription = sTempDescription; } // Price double getdPrice() { return dPrice; } void setdPrice( double dTempPrice) { dPrice = dTempPrice; } // Type..weight or unit int getiType() { return iType; } void setiType( int iTempType) { iType = iTempType; } // Inventory quantity double getdInventory() { return dInventory; } void setdInventory( double dTempInventory) { dInventory = dTempInventory; } private: int iPluCode; string sDescription; double dPrice; int iType; double dInventory; }; int main () { Product paInventory[21]; // Create inventory array Product paPurchase[21]; // Create customer purchase array // Constructor to open inventory input file ifstream InputInventory ("inventory.txt", ios::in); //If ifstream could not open the file if (!InputInventory) { cerr << "File could not be opened" << endl; exit (1); }//end if int x = 0; while (!InputInventory.eof () ) { int iTempPluCode; string sTempDescription; double dTempPrice; int iTempType; double dTempInventory; InputInventory >> iTempPluCode >> sTempDescription >> dTempPrice >> iTempType >> dTempInventory; paInventory[x].setiPluCode(iTempPluCode); paInventory[x].setsDescription(sTempDescription); paInventory[x].setdPrice(dTempPrice); paInventory[x].setiType(iTempType); paInventory[x].setdInventory(dTempInventory); x++; } bool bQuit = false; //CREATE MY TOTAL VARIABLE HERE! int iUserItemCount; do { int iUserPLUCode; double dUserAmount; double dAmountAvailable; int iProductIndex = -1; //CREATE MY SUBTOTAL VARIABLE HERE! while(iProductIndex == -1) { cout<<"Please enter the PLU Code of the product."<< endl; cin>>iUserPLUCode; for(int i = 0; i < 21; i++) { if(iUserPLUCode == paInventory[i].getiPluCode()) { dAmountAvailable = paInventory[i].getdInventory(); iProductIndex = i; } } //PLU code entry validation if(iProductIndex == -1) { cout << "You have entered an invalid PLU Code."; } } cout<<"Enter the quantity to buy.\n"<< "There are "<< dAmountAvailable << "available.\n"; cin>> dUserAmount; while(dUserAmount > dAmountAvailable) { cout<<"That's too many, please try again"; cin>>dUserAmount; } paPurchase[iUserItemCount].setiPluCode(iUserPLUCode);// Array of objects function calls paPurchase[iUserItemCount].setdInventory(dUserAmount); paPurchase[iUserItemCount].setdPrice(paInventory[iProductIndex].getdPrice()); paInventory[iProductIndex].setdInventory( paInventory[iProductIndex].getdInventory() - dUserAmount ); iUserItemCount++; cout <<"Are you done purchasing items? Enter 1 for yes and 0 for no.\n"; cin >> bQuit; //NOTE: Put Amount * quantity for subtotal //NOTE: Put code to update subtotal (total += subtotal) // NOTE: Need to create the output txt file! }while(!bQuit); return 0; }

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• C Class Instance from Void Pointer using Ctypes

  - by g.d.d.c

  I've got a C DLL that exposes a handful of methods that return void pointers to a Class like so: void *GetLicense() { static AppLicenseImpl ipds_; return (void *) &ipds_; } In C++, after loading the DLL, I'd do this to work with it: typedef void *(* FPGetLicense)(); GetLicense_ = (FPGetLicense)GetAddress("GetLicense"); license_ = (AppLicense *) GetLicense_(); license_->GetApplicationStatus(); // Load data so that other calls don't fail I can't figure out how to parallel that in Python. This gets me the pointer: d = ctypes.cdll.LoadLibrary('license.dll') d.GetLicense.restype = ctypes.c_void_p p = d.GetLicense() # returns ptr loc, something like 8791433660848L But I obviously can't call p.GetApplicationStatus() in Python. Does anyone have a suggestion on how I'd instantiate that Class the rest of the way in Python so that I can call GetApplicationStatus()?

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• Avoid incompatible pointer warning when dealing with double-indirection

  - by fnawothnig

  Assuming this program: #include <stdio.h> #include <string.h> static void ring_pool_alloc(void **p, size_t n) { static unsigned char pool[256], i = 0; *p = &pool[i]; i += n; } int main(void) { char *str; ring_pool_alloc(&str, 7); strcpy(str, "foobar"); printf("%s\n", str); return 0; } ... is it possible to somehow avoid the GCC warning test.c:12: warning: passing argument 1 of ‘ring_pool_alloc’ from incompatible pointer type test.c:4: note: expected ‘void **’ but argument is of type ‘char **’ ... without casting to (void**) (or simply disabling the compatibility checks)? Because I would very much like to keep compatibility warnings regarding indirection-level...

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• storing an integer constant other than zero in a pointer variable

  - by benjamin button

  int main() { int *d=0; printf("%d\n",*d); return 0; } this works fine. >cc legal.c > ./a.out 0 if i change the statement int *d=0; to int *d=1; i see the error. cc: "legal.c", line 6: error 1522: Cannot initialize a pointer with an integer constant other than zero. so its obvious that it will allow only zero.i want to know what happens inside the memory when we do this int *d=0 which is making it valid syntax. I am just asking this out of curiosity!

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