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

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

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  • C++ classes with members referencing each other

    - by Saad Imran.
    I'm trying to write 2 classes with members that reference each other. I'm not sure if I'm doing something wrong or it's just not possible. Can anyone help me out here... Source.cpp #include "Headers.h" using namespace std; void main() { Network* network = new Network(); system("pause"); return; } Headers.h #ifndef Headers_h #define Headers_h #include <iostream> #include <vector> #include "Network.h" #include "Router.h" #endif Network.h #include "Headers.h" class Network { protected: vector<Router> Routers; }; Router.h #include "Headers.h" class Router { protected: Network* network; public: }; The errors I'm getting are: error C2143: syntax error : missing ';' before '<' error C2238: unexpected token(s) preceding ';' error C4430: missing type specifier - int assumed. I'm pretty sure I'm not missing any semicolons or stuff like that. The program works find if I take out one of the members. I tried finding similar questions and the solution was to use pointers, but that's what I'm doing and it does't seem to be working!

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  • How to get a number closest to the average in c++?

    - by Alex Zielinski
    What I'm trying to achieve is to take the average of the numbers stored in the array and find the number which is closest to it. My code compiles, but has an error just after starting. I think it's something to do with the memory handling (I don't feel confident with pointers, etc. yet) Could some nice guy take a look at my code and tell me what's wrong with it? (don't be hard on me, I'm a beginner) #include <iostream> #include <cmath> using namespace std; double* aver(double* arr, size_t size, double& average); int main() { double arr[] = {1,2,3,4,5,7}; size_t size = sizeof(arr)/sizeof(arr[0]); double average = 0; double* p = aver(arr,size,average); cout << *p << " " << average << endl; } double* aver(double* arr, size_t size, double& average){ int i,j,sum; double* m = 0; int tmp[7]; for(i=0;i<size;i++) sum += arr[i]; average = sum/size; for(j=0;j<size;j++){ tmp[j] = arr[j] - average; if(abs(tmp[j])>*m) *m = tmp[j]; } return m; }

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  • C Nested Structure Pointer Problem

    - by Halo
    I have a shared structure, and inside it a request structure: struct shared_data { pthread_mutex_t th_mutex_queue; struct request_queue { int min; int max; char d_name[DIR_SIZE]; pid_t pid; int t_index; } request_queue[BUFSIZE]; int count; int data_buffer_allocation[BUFSIZE]; int data_buffers[BUFSIZE][100]; }; Then I prepare a request; struct shared_data *sdata_ptr; ... ... sdata_ptr->request_queue[index].pid = pid; strcpy(sdata_ptr->request_queue[index].d_name, dir_path_name); sdata_ptr->request_queue[index].min = min; sdata_ptr->request_queue[index].max = max; And the compiler warns me that I'm doing an incompatible implicit declaration in the strcpy function. I guess that's a problem with the pointers, but isn't what I wrote above supposed to be true?

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  • Mmap and structure

    - by blid..pl
    I'm working some code including communication between processes, using semaphores. I made structure like this: typedef struct container { sem_t resource, mutex; int counter; } container; and use in that way (in main app and the same in subordinate processes) container *memory; shm_unlink("MYSHM"); //just in case fd = shm_open("MYSHM", O_RDWR|O_CREAT|O_EXCL, 0); if(fd == -1) { printf("Error"); exit(EXIT_FAILURE); } memory = mmap(NULL, sizeof(container), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); ftruncate(fd, sizeof(container)); Everything is fine when I use one of the sem_ functions, but when I try to do something like memory->counter = 5; It doesn't work. Probably I got something wrong with pointers, but I tried almost everything and nothing seems to work. Maybe there's a better way to share variables, structures etc between processes ? Unfortunately I'm not allowed to use boost or something similiar, the code is for educational purposes and I'm intentend to keep as simple as it's possible.

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  • How does one create and use a pointer to an array of an unknown number of structures inside a class?

    - by user1658731
    Sorry for the confusing title... I've been playing around with C++, working on a project to parse a game's (Kerbal Space Program) save file so I can modify it and eventually send it over a network. I'm stuck with storing an unknown number of vessels and crew members, so I need to have an array of unknown size. Is this possible? I figured having a pointer to an array would be the way to go. I have: class SaveFileSystem { string version; string UT; int activeVessel; int numCrew; ??? Crews; // !! int numVessels; ??? Vessels; // !! } Where Crews and Vessels should be arrays of structures: struct Crew { string name; //Other stuff }; struct Vessel { string name; //Stuff }; I'm guessing I should have something like: this->Crews = new ???; this->Vessels = new ???; in my constructor to initialize the arrays, and attempt to access it with: this->Crews[0].name = "Ship Number One"; Does this make any sense??? I'd expect the "???"'s to involve a mess of asterisk's, like "*struct (*)Crews" but I have no real idea. I've got normal pointers down and such, but this is a tad over my head... I'd like to access the structures like in the last snippet, but if C++ doesn't like that I could do pointer arithmetic. I've looked into vectors, but I have an unhealthy obsession with efficiency, and it really pains me how you don't know what's going on behind it.

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  • Having issues with initializing character array

    - by quandrum
    Ok, this is for homework about hashtables, but this is the simple stuff I thought I was able to do from earlier classes, and I'm tearing my hair out. The professor is not being responsive enough, so I thought I'd try here. We have a hashtable of stock objects.The stock objects are created like so: stock("IBM", "International Business Machines", 2573, date(date::MAY, 23, 1967)) my constructor looks like: stock::stock(char const * const symbol, char const * const name, int sharePrice, date priceDate): symbol(NULL), name(NULL), sharePrice(sharePrice), dateOfPrice(priceDate) { setSymbol(symbol); setName(name); } and setSymbol looks like this: (setName is indentical): void stock::setSymbol(const char* symbol) { if (this->symbol) delete [] this->symbol; this->symbol = new char[strlen(symbol)+1]; strcpy(this->symbol,symbol); } and it refuses to allocate on the line this->symbol = new char[strlen(symbol)+1]; with a std::bad_alloc. name and symbol are declared char * name; char * symbol; I feel like this is exactly how I've done it in previous code.I'm sure it's something silly with pointers. Can anyone help?

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  • Hashtable resizing leaks memory

    - by thpetrus
    I wrote a hashtable and it basically consists of these two structures: typedef struct dictEntry { void *key; void *value; struct dictEntry *next; } dictEntry; typedef struct dict { dictEntry **table; unsigned long size; unsigned long items; } dict; dict.table is a multidimensional array, which contains all the stored key/value pair, which again are a linked list. If half of the hashtable is full, I expand it by doubling the size and rehashing it: dict *_dictRehash(dict *d) { int i; dict *_d; dictEntry *dit; _d = dictCreate(d->size * 2); for (i = 0; i < d->size; i++) { for (dit = d->table[i]; dit != NULL; dit = dit->next) { _dictAddRaw(_d, dit); } } /* FIXME memory leak because the old dict can never be freed */ free(d); // seg fault return _d; } The function above uses the pointers from the old hash table and stores it in the newly created one. When freeing the old dict d a Segmentation Fault occurs. How am I able to free the old hashtable struct without having to allocate the memory for the key/value pairs again?

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  • How do I cast a void pointer to a struct in C?

    - by Rowhawn
    In a project I'm writing code for, I have a void pointer, "implementation", which is a member of a "Hash_map" struct, and points to an "Array_hash_map" struct. The concepts behind this project are not very realistic, but bear with me. The specifications of the project ask that I cast the void pointer "implementation" to an "Array_hash_map" before I can use it in any functions. My question, specifically is, what do I do in the functions to cast the void pointers to the desired struct? Is there one statement at the top of each function that casts them or do I make the cast every time I use "implementation"? Here are the typedefs the structs of a Hash_map and Array_hash_map as well as a couple functions making use of them. typedef struct { Key_compare_fn key_compare_fn; Key_delete_fn key_delete_fn; Data_compare_fn data_compare_fn; Data_delete_fn data_delete_fn; void *implementation; } Hash_map; typedef struct Array_hash_map{ struct Unit *array; int size; int capacity; } Array_hash_map; typedef struct Unit{ Key key; Data data; } Unit; functions: /* Sets the value parameter to the value associated with the key parameter in the Hash_map. */ int get(Hash_map *map, Key key, Data *value){ int i; if (map == NULL || value == NULL) return 0; for (i = 0; i < map->implementation->size; i++){ if (map->key_compare_fn(map->implementation->array[i].key, key) == 0){ *value = map->implementation->array[i].data; return 1; } } return 0; } /* Returns the number of values that can be stored in the Hash_map, since it is represented by an array. */ int current_capacity(Hash_map map){ return map.implementation->capacity; }

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  • How to enforce users to create objects of class derived from mine with "new" only?

    - by sharptooth
    To implement reference counting we use an IUnknown-like interface and a smart pointer template class. The interface has implementation for all the reference-count methods, including Release(): void IUnknownLike::Release() { if( --refCount == 0 ) { delete this; } } The smart pointer template class has a copy constructor and an assignment operator both accepting raw pointers. So users can do the following: class Class : public IUnknownLike { }; void someFunction( CSmartPointer<Class> object ); //whatever function Class object; someFunction( &object ); and the program runs into undefined behavior - the object is created with reference count zero, the smart pointer is constructed and bumps it to one, then the function returns, smart pointer is destroyed, calls Release() which leads to delete of a stack-allocated variable. Users can as well do the following: struct COuter { //whatever else; Class inner;// IUnknownLike descendant }; COuter object; somefunction( &object.Inner ); and again an object not created with new is deleted. Undefined behavior at its best. Is there any way to change the IUnknownLike interface so that the user is forced to use new for creating all objects derived from IUnknownLike - both directly derived and indirectly derived (with classes in between the most derived and the base)?

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  • why i^=j^=i^=j isn't equal to *i^=*j^=*i^=*j

    - by klvoek
    In c , when there is variables (assume both as int) i less than j , we can use the equation i^=j^=i^=j to exchange the value of the two variables. For example, let int i = 3, j = 5; after computed i^=j^=i^=j, I got i = 5, j = 3 . What is so amazing to me. But, if i use two int pointers to re-do this , with *i^=*j^=*i^=*j , use the example above what i got will be i = 0 and j = 3. Then, describe it simply: In C 1 int i=3, j=5; i^=j^=i^=j; // after this i = 5, j=3 2 int i = 3, j= 5; int *pi = &i, *pj = &j; *pi^=*pj^=*pi^=*pj; // after this, $pi = 0, *pj = 5 In JavaScript var i=3, j=5; i^=j^=i^=j; // after this, i = 0, j= 3 the result in JavaScript makes this more interesting to me my sample code , on ubuntu server 11.0 & gcc #include <stdio.h> int main(){ int i=7, j=9; int *pi=&i, *pj=&j; i^=j^=i^=j; printf("i=%d j=%d\n", i, j); i=7, j==9; *pi^=*pj^=*pi^=*pj printf("i=%d j=%d\n", *pi, *pj); } however, i had spent hours to test and find out why, but nothing means. So, please help me. Or, just only i made some mistake???

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  • Split UInt32 (audio frame) into two SInt16s (left and right)?

    - by morgancodes
    Total noob to anything lower-level than Java, diving into iPhone audio, and realing from all of the casting/pointers/raw memory access. I'm working with some example code wich reads a WAV file from disc and returns stereo samples as single UInt32 values. If I understand correctly, this is just a convenient way to return the 32 bits of memory required to create two 16 bit samples. Eventually this data gets written to a buffer, and an audio unit picks it up down the road. Even though the data is written in UInt32-sized chunks, it eventually is interpreted as pairs of 16-bit samples. What I need help with is splitting these UInt32 frames into left and right samples. I'm assuming I'll want to convert each UInt32 into an SInt16, since an audio sample is a signed value. It seems to me that for efficiency's sake, I ought to be able to simply point to the same blocks in memory, and avoid any copying. So, in pseudo-code, it would be something like this: UInt32 myStereoFrame = getFramefromFilePlayer; SInt16* leftChannel = getFirst16Bits(myStereoFrame); SInt16* rightChannel = getSecond16Bits(myStereoFrame); Can anyone help me turn my pseudo into real code?

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  • Creating a new object destroys an older object with different name in C++

    - by Mikael
    First question here! So, I am having some problems with pointers in Visual C++ 2008. I'm writing a program which will control six cameras and do some processing on them so to clean things up I have created a Camera Manager class. This class handles all operations which will be carried out on all the cameras. Below this is a Camera class which interacts with each individual camera driver and does some basic image processing. Now, the idea is that when the manager is initialised it creates two cameras and adds them to a vector so that I can access them later. The catch here is that when I create the second camera (camera2) the first camera's destructor is called for some reason, which then disconnects the camera. Normally I'd assume that the problem is somewhere in the Camera class, but in this case everything works perfectly as long as I don't create the camera2 object. What's gone wrong? CameraManager.h: #include "stdafx.h" #include <vector> #include "Camera.h" class CameraManager{ std::vector<Camera> cameras; public: CameraManager(); ~CameraManager(); void CaptureAll(); void ShowAll(); }; CameraManager.cpp: #include "stdafx.h" #include "CameraManager.h" CameraManager::CameraManager() { printf("Camera Manager: Initializing\n"); [...] Camera *camera1 = new Camera(NodeInfo,1, -44,0,0); cameras.push_back(*camera1); // Adding the following two lines causes camera1's destructor to be called. Why? Camera *camera2 = new Camera(NodeInfo,0, 44,0,0); cameras.push_back(*camera2); printf("Camera Manager: Ready\n"); }

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  • C Programming - Passing a pointer to array

    - by Pedro
    How do I pass a pointer value to an array of the struct; For example, on a txt I have this: John Doe;[email protected];214425532; My code: typedef struct Person{ char name[100]; char email[100]; int phone; }PERSON; int main(){ PERSON persons[100]; FILE *fp; char *ap_name; char *ap_email; char *ap_phone; char line[100]; fp=("text.txt","r"); if(fp==NULL){ exit(1); } else{ fgets(line,100,fp); ap_name=strtok(line,";"); ap_email=strtok(NULL,";"); ap_phone=strtok(NULL,";"); } return 0; } My question is how can I pass the value of ap_name, ap_email, ap_phone to the struct? And, do I need to use all of these pointers?

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  • How can i create an n-dimensional array in c

    - by shortCircuit
    I was thinking of making a function that would accept the size of array as a parameter and create a n dimensional array. My room-mate took the liberty of making it complex. He said lets write a function that takes n parameters and returns an n-dimensional array using those parameters as the dimensions. Now i realize an one-day and d array is easy to implement with pointers. For 2d array the snippet would be something like (standard way) : int** x; int* temp; x = (int**)malloc(m * sizeof(int*)); temp = (int*)malloc(m*n * sizeof(int)); for (int i = 0; i < m; i++) { x[i] = temp + (i * n); } where the array is of size m*n; But the problem lies how do we find the nested loop parameters for a n-dimensional array? Is there any way to optimize the code?

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  • Interpretation of int (*a)[3]

    - by kapuzineralex
    When working with arrays and pointers in C, one quickly discovers that they are by no means equivalent although it might seem so at a first glance. I know about the differences in L-values and R-values. Still, recently I tried to find out the type of a pointer that I could use in conjunction with a two-dimensional array, i.e. int foo[2][3]; int (*a)[3] = foo; However, I just can't find out how the compiler "understands" the type definition of a in spite of the regular operator precedence rules for * and []. If instead I were to use a typedef, the problem becomes significantly simpler: int foo[2][3]; typedef int my_t[3]; my_t *a = foo; At the bottom line, can someone answer me the questions as to how the term int (*a)[3] is read by the compiler? int a[3] is simple, int *a[3] is simple as well. But then, why is it not int *(a[3])? EDIT: Of course, instead of "typecast" I meant "typedef" (it was just a typo).

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  • Automatically converting an A* into a B*

    - by Xavier Nodet
    Hi, Suppose I'm given a class A. I would like to wrap pointers to it into a small class B, some kind of smart pointer, with the constraint that a B* is automatically converted to an A* so that I don't need to rewrite the code that already uses A*. I would therefore want to modify B so that the following compiles... struct A { void foo() {} }; template <class K> struct B { B(K* k) : _k(k) {} //operator K*() {return _k;} //K* operator->() {return _k;} private: K* _k; }; void doSomething(A*) {} void test() { A a; A* pointer_to_a (&a); B<A> b (pointer_to_a); //b->foo(); // I don't need those two... //doSomething(b); B<A>* pointer_to_b (&b); pointer_to_b->foo(); // 'foo' : is not a member of 'B<K>' doSomething(pointer_to_b); // 'doSomething' : cannot convert parameter 1 from 'B<K> *' to 'A *' } Note that B inheriting from A is not an option (instances of A are created in factories out of my control)... Is it possible? Thanks.

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  • Pointer and malloc issue

    - by Andy
    I am fairly new to C and am getting stuck with arrays and pointers when they refer to strings. I can ask for input of 2 numbers (ints) and then return the one I want (first number or second number) without any issues. But when I request names and try to return them, the program crashes after I enter the first name and not sure why. In theory I am looking to reserve memory for the first name, and then expand it to include a second name. Can anyone explain why this breaks? Thanks! #include <stdio.h> #include <stdlib.h> void main () { int NumItems = 0; NumItems += 1; char* NameList = malloc(sizeof(char[10])*NumItems); printf("Please enter name #1: \n"); scanf("%9s", NameList[0]); fpurge(stdin); NumItems += 1; NameList = realloc(NameList,sizeof(char[10])*NumItems); printf("Please enter name #2: \n"); scanf("%9s", NameList[1]); fpurge(stdin); printf("The first name is: %s",NameList[0]); printf("The second name is: %s",NameList[1]); return 0; }

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  • Public class: Makes pointer from integer without cast

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

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  • How to queue and call actual methods (rather than immediately eval) in java?

    - by alleywayjack
    There are a list of tasks that are time sensitive (but "time" in this case is arbitrary to what another program tells me - it's more like "ticks" rather than time). However, I do NOT want said methods to evaluate immediately. I want one to execute after the other finished. I'm using a linked list for my queue, but I'm not really sure how/if I can access the actual methods in a class without evaluating them immediate. The code would look something like... LinkedList<Method> l = new LinkedList<Method>(); l.add( this.move(4) ); l.add( this.read() ); l.removeFirst().call(); //wait 80 ticks l.removeFirst().call(); move(4) would execute immediately, then 80 ticks later, I would remove it from the list and call this.read() which would then be executed. I'm assuming this has to do with the reflection classes, and I've poked around a bit, but I can't seem to get anything to work, or do what I want. If only I could use pointers...

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  • Strange code behaviour?

    - by goldenmean
    Hi, I have a C code in which i have a structure declaration which has an array of int[576] declared in it. For some reason, i had to remove this array from the structure, So i replaced this array with a pointer as int *ptr; declared some global array of same type, somewhere else in the code, and initialized this pointer by assigning the global array to this pointer. So i did not have to change the way i was accessing this array, from other parts of my code. But it works fine/gives desired output when i have the array declared in the structure, but it gives junk output when i declare it as a pointer in the structure and assign a global array to this pointer, as a part of the pointer initialization. All this code is being run on MS-VC 6.0/Windows setup/Intel-x86. I tried below things: 1)Suspected structure padding/alignment but could not get any leads? If at all structure alignment could be a culprit how can i proceed to narrow it down and confirm it? 2) I have made sure that in both cases the array is initialized to some default values, say 0 before its first use, and its not being used before initialization. 3)I tried using global array as well as malloc based memory for this newly declared array. Same result, junk output. Am i missing something? How can i zero down the problem. Any pointers would be helpful. Thanks, -AD.

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  • Misaligned Pointer Performance

    - by Elite Mx
    Aren't misaligned pointers (in the BEST possible case) supposed to slow down performance and in the worst case crash your program (assuming the compiler was nice enough to compile your invalid c program). Well, the following code doesn't seem to have any performance differences between the aligned and misaligned versions. Why is that? /* brutality.c */ #ifdef BRUTALITY xs = (unsigned long *) ((unsigned char *) xs + 1); #endif ... /* main.c */ #include <stdio.h> #include <stdlib.h> #define size_t_max ((size_t)-1) #define max_count(var) (size_t_max / (sizeof var)) int main(int argc, char *argv[]) { unsigned long sum, *xs, *itr, *xs_end; size_t element_count = max_count(*xs) >> 4; xs = malloc(element_count * (sizeof *xs)); if(!xs) exit(1); xs_end = xs + element_count - 1; sum = 0; for(itr = xs; itr < xs_end; itr++) *itr = 0; #include "brutality.c" itr = xs; while(itr < xs_end) sum += *itr++; printf("%lu\n", sum); /* we could free the malloc-ed memory here */ /* but we are almost done */ exit(0); } Compiled and tested on two separate machines using gcc -pedantic -Wall -O0 -std=c99 main.c for i in {0..9}; do time ./a.out; done

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  • How to implement a Linked List in Java?

    - by nbarraille
    Hello! I am trying to implement a simple HashTable in Java that uses a Linked List for collision resolution, which is pretty easy to do in C, but I don't know how to do it in Java, as you can't use pointers... First, I know that those structures are already implemented in Java, I'm not planning on using it, just training here... So I created an element, which is a string and a pointer to the next Element: public class Element{ private String s; private Element next; public Element(String s){ this.s = s; this.next = null; } public void setNext(Element e){ this.next = e; } public String getString(){ return this.s; } public Element getNext(){ return this.next; } @Override public String toString() { return "[" + s + "] => "; } } Of course, my HashTable has an array of Element to stock the data: public class CustomHashTable { private Element[] data; Here is my problem: For example I want to implement a method that adds an element AT THE END of the linked List (I know it would have been simpler and more efficient to insert the element at the beginning of the list, but again, this is only for training purposes). How do I do that without pointer? Here is my code (which could work if e was a pointer...): public void add(String s){ int index = hash(s) % data.length; System.out.println("Adding at index: " + index); Element e = this.data[index]; while(e != null){ e = e.getNext(); } e = new Element(s); } Thanks!

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  • C++0x Smart Pointer Comparisons: Inconsistent, what's the rationale?

    - by GManNickG
    In C++0x (n3126), smart pointers can be compared, both relationally and for equality. However, the way this is done seems inconsistent to me. For example, shared_ptr defines operator< be equivalent to: template <typename T, typename U> bool operator<(const shared_ptr<T>& a, const shared_ptr<T>& b) { return std::less<void*>()(a.get(), b.get()); } Using std::less provides total ordering with respect to pointer values, unlike a vanilla relational pointer comparison, which is unspecified. However, unique_ptr defines the same operator as: template <typename T1, typename D1, typename T2, typename D2> bool operator<(const unique_ptr<T1, D1>& a, const unique_ptr<T2, D2>& b) { return a.get() < b.get(); } It also defined the other relational operators in similar fashion. Why the change in method and "completeness"? That is, why does shared_ptr use std::less while unique_ptr uses the built-in operator<? And why doesn't shared_ptr also provide the other relational operators, like unique_ptr? I can understand the rationale behind either choice: with respect to method: it represents a pointer so just use the built-in pointer operators, versus it needs to be usable within an associative container so provide total ordering (like a vanilla pointer would get with the default std::less predicate template argument) with respect to completeness: it represents a pointer so provide all the same comparisons as a pointer, versus it is a class type and only needs to be less-than comparable to be used in an associative container, so only provide that requirement But I don't see why the choice changes depending on the smart pointer type. What am I missing? Bonus/related: std::shared_ptr seems to have followed from boost::shared_ptr, and the latter omits the other relational operators "by design" (and so std::shared_ptr does too). Why is this?

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  • How do I reset my pointer to a specific array location?

    - by ohtanya
    I am a brand new programming student, so please forgive my ignorance. My assignment states: Write a program that declares an array of 10 integers. Write a loop that accepts 10 values from the keyboard and write another loop that displays the 10 values. Do not use any subscripts within the two loops; use pointers only. Here is my code: #include "stdafx.h" #include <iostream> using namespace std; int main() { const int NUM = 10; int values[NUM]; int *p = &values[0]; int x; for(x = 0; x < NUM; ++x, ++p) { cout << "Enter a value: "; cin >> *p; } for(x = 0; x < NUM; ++x, ++p) { cout << *p << " "; } return 0; } I think I know where my problem is. After my first loop, my pointer is at values[10], but I need to get it back to values[0] to display them. How can I do that?

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