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• How to implement square root and exponentiation on arbitrary length numbers?

  - by tomp

  I'm working on new data type for arbitrary length numbers (only non-negative integers) and I got stuck at implementing square root and exponentiation functions (only for natural exponents). Please help. I store the arbitrary length number as a string, so all operations are made char by char. Please don't include advices to use different (existing) library or other way to store the number than string. It's meant to be a programming exercise, not a real-world application, so optimization and performance are not so necessary. If you include code in your answer, I would prefer it to be in either pseudo-code or in C++. The important thing is the algorithm, not the implementation itself. Thanks for the help.

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• Specialization of template method - what's wrong with my code?

  - by Vincenzo

  What's wrong with this code? class School { public: template<typename T> size_t count() const; private: vector<Boy*> boys; vector<Girl*> girls; } template<> size_t School::count<Boy>() const { return boys.size(); } My compile says that "specialization of .. after initialization". Could you please help?

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• Should I call class destructor in this code?

  - by peterg

  I am using this sample to decode/encode some data I am retrieving/sending from/to a web server, and I want to use it like this: BOOL HandleMessage(UINT uMsg,WPARAM wParam,LPARAM lParam,LRESULT* r) { if(uMsg == WM_DESTROY) { PostQuitMessage(0); return TRUE; } else if(uMsg == WM_CREATE) { // Start timer StartTimer(); return TRUE; } else if(uMsg == WM_TIMER) { //get data from server char * test = "test data"; Base64 base64; char *temp = base64.decode(test); MessageBox(TEXT(temp), 0, 0); } } The timer is set every 5 minutes. Should I use delete base64 at the end? Does delete deallocates everything used by base64?

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• error in encryption program

  - by Raja

  #include<iostream> #include<math.h> #include<string> using namespace std; int gcd(int n,int m) { if(m<=n && n%m ==0) return m; if(n<m) return gcd(m,n); else return gcd(m,n%m); } int REncryptText(char m) { int p = 11, q = 3; int e = 3; int n = p * q; int phi = (p - 1) * (q - 1); int check1 = gcd(e, p - 1); int check2 = gcd(e, q - 1); int check3 = gcd(e, phi); // // Compute d such that ed = 1 (mod phi) //i.e. compute d = e-1 mod phi = 3-1 mod 20 //i.e. find a value for d such that phi divides (ed-1) //i.e. find d such that 20 divides 3d-1. //Simple testing (d = 1, 2, ...) gives d = 7 // double d = Math.Pow(e, -1) % phi; int d = 7; // public key = (n,e) // (33,3) //private key = (n,d) //(33 ,7) double g = pow(m,e); int ciphertext = g %n; // Now say we want to encrypt the message m = 7, c = me mod n = 73 mod 33 = 343 mod 33 = 13. Hence the ciphertext c = 13. //double decrypt = Math.Pow(ciphertext, d) % n; return ciphertext; } int main() { char plaintext[80],str[80]; cout<<" enter the text you want to encrpt"; cin.get(plaintext,79); int l =strlen(plaintext); for ( int i =0 ; i<l ; i++) { char s = plaintext[i]; str[i]=REncryptText(s); } for ( int i =0 ; i<l ; i++) { cout<<"the encryption of string"<<endl; cout<<str[i]; } return 0; }

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• help me with xor encryption in c#

  - by x86shadow

  I wrote this code in c# to encrypt a text with a key : using System; using System.Linq; using System.Collections.Generic; using System.Text; namespace ENCRYPT { class XORENC { private static int Bin2Dec(string num) { int _num = 0; for (int i = 0; i < num.Length; i++) { _num += (int)Math.Pow(2, num.Length - i - 1) * int.Parse(num[i].ToString()); } return _num; } private static string Dec2Bin(int num) { if (num < 2) return num.ToString(); return Dec2Bin(num / 2) + (num % 2).ToString(); } public static string StrXor(string str, string key) { string _str = ""; string _key = ""; string _dec = ""; string _temp = ""; for (int i = 0; i < str.Length; i++) { _temp = Dec2Bin(str[i]); for (int j = 0; j < 8 - _temp.Length + 1; j++) { _temp = '0' + _temp; } _str += _temp; } for (int i = 0; i < key.Length; i++) { _temp = Dec2Bin(key[i]); for (int j = 0; j < 8 - _temp.Length + 1; j++) { _temp = '0' + _temp; } _key += _temp; } while (_key.Length < _str.Length) { _key += _key; } if (_key.Length > _str.Length) _key = _key.Substring(0, _str.Length); for (int i = 0; i < _str.Length; i++) { if (_str[i] == _key[i]) { _dec += '0'; } else { _dec += '1'; } } _str = ""; for (int i = 0; i < _dec.Length; i = i + 8) { char _chr = (char)0; _chr = (char)Bin2Dec(_dec.Substring(i, 8)); _str += _chr; } return _str; } } } the problem is that I always get error when I want to decrypt an encryted text with this code. see the example below for more info : string enc_text = ENCRYPT.XORENC("abc","a"); //enc_text = " ??" string dec_text = ENCRYPT.XORENC(enc_text,"a"); //ERROR any one can help ?

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• Can someone explain how pointer to pointer works?

  - by user3549560

  I don't really understand how the pointer to pointer works. Any way to do the same work without using pointer to pointer? struct customer{ char name[20]; char surname[20]; int code; float money; }; typedef struct customer customer; void inserts(customer **tmp) { *tmp = (customer*)malloc(sizeof(customer)); puts("Give me a customer name, surname code and money"); scanf("%s %s %d %f", (*tmp)->name, (*tmp)->surname, &(*tmp)->code,&(*tmp)->money); }

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• How return a std::string from C's "getcwd" function

  - by rubenvb

  Sorry to keep hammering on this, but I'm trying to learn :). Is this any good? And yes, I care about memory leaks. I can't find a decent way of preallocating the char*, because there simply seems to be no cross-platform way. const string getcwd() { char* a_cwd = getcwd(NULL,0); string s_cwd(a_cwd); free(a_cwd); return s_cwd; } UPDATE2: without Boost or Qt, the most common stuff can get long-winded (see accepted answer)

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• How to free memory in try-catch blocks?

  - by Kra

  Hi, I have a simple question hopefully - how does one free memory which was allocated in the try block when the exception occurs? Consider the following code: try { char *heap = new char [50]; //let exception occur here delete[] heap; } catch (...) { cout << "Error, leaving function now"; //delete[] heap; doesn't work of course, heap is unknown to compiler return 1; } How can I free memory after the heap was allocated and exception occurred before calling delete[] heap? Is there a rule not to allocate memory on heap in these try .. catch blocks? Thanks

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• C pointer array scope and function calls

  - by juvenis

  I have this situation: { float foo[10]; for (int i = 0; i < 10; i++) { foo[i] = 1.0f; } object.function1(foo); // stores the float pointer to a const void* member of object } object.function2(); // uses the stored void pointer Are the contents of the float pointer unknown in the second function call? It seems that I get weird results when I run my program. But if I declare the float foo[10] to be const and initialize it in the declaration, I get correct results. Why is this happening?

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• Haskell. Numbers in binary numbers. words

  - by Katja

  Hi! I need to code words into binary numbers. IN: "BCD..." OUT:1011... I have written already funktion for coding characters into siple numbers IN: 'C' OUT: 3 IN: 'c' OUT: 3 lett2num :: Char -> Int lett2num x | (ord 'A' <= ord x) && (ord x <= ord 'Z') = (ord x - ord 'A') + 1 | (ord 'a' <= ord x) && (ord x <= ord 'z') = (ord x - ord 'a') +1 num2lett :: Int -> Char num2lett n | (n <= ord 'A') && (n <= ord 'Z') = chr(ord 'A'+ n - 1) | (n <= ord 'a') && (n <= ord 'Z') = chr(ord 'A'+ n - 1) I wrote as well function for codind simple numbers into binary. num2bin :: Int->[Int] num2bin 0 = [] num2bin n | n>=0 = n `mod` 2 : (num2bin( n `div` 2)) | otherwise = error but I donw want those binary numbers to be in a list how can I get rid of the lists? Thanks

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• How to return a string literal from a function

  - by skydoor

  Hi I am always confused about return a string literal or a string from a function. I was told that there might be memory leak because you don't know when the memory will be deleted? For example, in the code below, how to implement foo() so that make the output of the code is "Hello World"? void foo ( ) // you can add parameters here. { } int main () { char *c; foo ( ); printf ("%s",c); return 0; } Also if the return type of foo() is not void, but you can return char*, what should it be.

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• How to sanely read and dump structs to disk when some fields are pointers?

  - by bp

  Hello, I'm writing a FUSE plugin in C. I'm keeping track of data structures in the filesystem through structs like: typedef struct { block_number_t inode; filename_t filename; //char[SOME_SIZE] some_other_field_t other_field; } fs_directory_table_item_t; Obviously, I have to read (write) these structs from (to) disk at some point. I could treat the struct as a sequence of bytes and do something like this: read(disk_fd, directory_table_item, sizeof(fs_directory_table_item_t)); ...except that cannot possibly work as filename is actually a pointer to the char array. I'd really like to avoid having to write code like: read(disk_df, *directory_table_item.inode, sizeof(block_number_t)); read(disk_df, directory_table_item.filename, sizeof(filename_t)); read(disk_df, *directory_table_item.other_field, sizeof(some_other_field_t)); ...for each struct in the code, because I'd have to replicate code and changes in no less than three different places (definition, reading, writing). Any DRYer but still maintainable ideas?

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• number of months between two dates - using boost's date

  - by MartinP

  I've used boost::gregorian::date a bit now. I can see that there are the related months & years & weeks duration types. I can see how to use known durations to advance a given date. Qu: But how can I get the difference between two dates in months (or years or weeks) ? I was hoping to find a function like: template<typename DURATION> DURATION date_diff<DURATION>(const date& d1,const date& d2); There would need to be some handling of rounding too.

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

  - by WSkinner

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

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• some logical error in taking up character in java

  - by Himanshu Aggarwal

  This is my code... class info{ public static void main (String[]args) throws IOException{ char gen; while(true) { //problem occurs with this while System.out.print("\nENTER YOUR GENDER (M/F) : "); gen=(char)System.in.read(); if(gen=='M' || gen=='F' || gen=='m' || gen=='f'){ break; } } System.out.println("\nGENDER = "+gen); } } This is my output... ENTER YOUR GENDER (M/F) : h ENTER YOUR GENDER (M/F) : ENTER YOUR GENDER (M/F) : ENTER YOUR GENDER (M/F) : m GENDER = m Could someone please help me understand why it is asking for the gender so many times.

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• Assigning large UInt32 constants in VB.Net

  - by Kumba

  I inquired on VB's erratic behavior of treating all numerics as signed types back in this question, and from the accepted answer there, was able to get by. Per that answer: Visual Basic Literals Also keep in mind you can add literals to your code in VB.net and explicitly state constants as unsigned. So I tried this: Friend Const POW_1_32 As UInt32 = 4294967296UI And VB.NET throws an Overflow error in the IDE. Pulling out the integer overflow checks doesn't seem to help -- this appears to be a flaw in the IDE itself. This, however, doesn't generate an error: Friend Const POW_1_32 As UInt64 = 4294967296UL So this suggests to me that the IDE isn't properly parsing the code and understanding the difference between Int32 and UInt32. Any suggested workarounds and/or possible clues on when MS will make unsigned data types intrinsic to the framework instead of the hacks they currently are?

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• C# StringBuilder question

  - by andrew

  in a C# file i have a class Archiver { [DllImport("Archiver.dll")] public static extern void archive(string data, StringBuilder response); } string data is an input, and StringBuilder response is where the function writes something the archive function prototype (written in C) looks like this: void archive(char * dataChr, char * outChr); and it receives a string in dataChr, and then does a strcpy(outChr,"some big text"); from C# i call it something like this: string message = "some text here"; StringBuilder response = new StringBuilder(10000); Archiver.archive(message,response); this works, but the problem, as you might see is that i give a value to the StringBuilder size, but the archive function might give back a (way) larger text than the size i've given to my StringBuilder. any way to fix this?

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• inline and member initializers

  - by Alexander

  When should I inline a member function and when should I use member initializers? My code is below.. I would like to modify it so I could make use some inline when appropriate and member initializers: #include "Books.h" Book::Book(){ nm = (char*)""; thck = 0; wght = 0; } Book::Book(const char *name, int thickness, int weight){ nm = strdup(name); thck = thickness; wght = weight; } Book::~Book(){ } const char* Book::name(){ return nm; } int Book::thickness(){ return thck; } int Book::weight(){ return wght; } // // Prints information about the book using this format: // "%s (%d mm, %d dg)\n" // void Book::print(){ printf("%s (%d mm, %d dg)\n", nm, thck, wght); } Bookcase::Bookcase(int id){ my_id = id; no_shelf = 0; } int Bookcase::id(){ return my_id; } Bookcase::~Bookcase(){ for (int i = 0; i < no_shelf; i++) delete my_shelf[i]; } bool Bookcase::addShelf(int width, int capacity){ if(no_shelf == 10) return false; else{ my_shelf[no_shelf] = new Shelf(width, capacity); no_shelf++; return true; } } bool Bookcase::add(Book *bp){ int index = -1; int temp_space = -1; for (int i = 0; i < no_shelf; i++){ if (bp->weight() + my_shelf[i]->curCapacity() <= my_shelf[i]->capacity()){ if (bp->thickness() + my_shelf[i]->curWidth() <= my_shelf[i]->width() && temp_space < (my_shelf[i]->width() - my_shelf[i]->curWidth())){ temp_space = (my_shelf[i]->width()- my_shelf[i]->curWidth()); index = i; } } } if (index != -1){ my_shelf[index]->add(bp); return true; }else return false; } void Bookcase::print(){ printf("Bookcase #%d\n", my_id); for (int i = 0; i < no_shelf; i++){ printf("--- Shelf (%d mm, %d dg) ---\n", my_shelf[i]->width(), my_shelf[i]->capacity()); my_shelf[i]->print(); } }

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• Legality Of Re-Implementing An Existing API (e.g. GNU implementing the UNIX APIs)

  - by splicer

  I've often wondered about this. I'm not looking for legal advice, just casual opinions ;) If some company publishes an API on the web for their closed-source library, would it be legal for another party to release an open-source implementation of that API? Are function declarations considered source code? Take GNU implementing the UNIX APIs, for example. The UNIX standard gives the following function declaration and defines its required behaviour in English: char * mktemp(char *template); Now, consider an API that lists and declares and describes several thousand (more much complex) functions, enums, etc.; an API which defines a solution to a non-trival set of problems. If an open-source project publishes C headers that copy (verbatim) the function definitions contained in the closed-source company's published API, doesn't that violate some sort copyright law?

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• abstract class in C++

  - by Alexander

  I have a derived derived class from an abstract class. The code is below. I have a FishTank class which is derived from an Aquarium and Aquarium is derived from item. My question is that should I put the definition of virtual int minWidth() const = 0; in aquarium again or is the code below sufficient? class Item{ public: virtual int minWidth() const = 0; }; class Aquarium{ public: virtual int calWidth() = 0; // Pure virtual function. }; class FishTank : public Aquarium{ public: FishTank(int base1, int base2, int height); ~FishTank(); int calWidth(); int minWidth(); };

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• Sorting array of structs

  - by mrblippy

  Hi, i am having trouble making a method to sort an array of structs. i am tring to sort them in ascending order based on classcode. any help you could give would be appreciated struct unit { char classcode[4]; char *classname; }; void insertion_sort(struct unit u[], int n) { int j, p; struct unit tmp[1]; for(p = 1; p < n; p++) { tmp[0] = u[p]; for(j = p; j > 0 && (strcmp(tmp[j-1].classcode, tmp[p].classcode) > 0); j--) u[j] = u[j-1]; u[j] = tmp[0]; } }

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• Difference between debug and release.

  - by atch

  Why when I'm debugging in debug mode everything in code below works as suppose to but when I switch to release I'm getting strange result? void say_hello(int argc, char* argv[])//In release mode argc has different values from 124353625 to 36369852 <include iostream> { std::cout << "In say_hello()\n"; } int main(int argc, char* argv[]) { say_hello(3,argv);//when instead of literal I enter "argc" everything is ok. return 0; } Thanks for help.

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• How to get Doxygen to recognize custom latex command

  - by Halpo

  Is there a way to use extra latex packages and/or extra latex commands with Doxygen code documentation system. For example I define the shortcut in a custom sty file. \newcommand{\tf}{\Theta_f} Then I use it about 300 time in the code, which is across about a dozen files. /*! Stochastic approximation of the latent response*/ void dual_bc_genw( //... double const * const psi, ///< \f$ \psi = B\tf \f$ //... ){/* lots of brilliant code */} But how do I get the system to recognize the extra package.

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• Is calling of overload operator-> resolved at compile time?

  - by Brent

  when I tried to compile the code: (note: func and func2 is not typo) struct S { void func2() {} }; class O { public: inline S* operator->() const; private: S* ses; }; inline S* O::operator->() const { return ses; } int main() { O object; object->func(); return 0; } there is a compile error reported: D:\code>g++ operatorp.cpp -S -o operatorp.exe operatorp.cpp: In function `int main()': operatorp.cpp:27: error: 'struct S' has no member named 'func' it seems that invoke the overloaded function of "operator-" is done during compile time? I'd added "-S" option for compile only.

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• Hiredis waiting for message

  - by Vivek Goel

  I am using hiredis C library to connect to redis server. I am not able to figure out how to wait for new messages after subscribing to new message. My code look like: signal(SIGPIPE, SIG_IGN ); struct event_base *base = event_base_new(); redisAsyncContext *c = redisAsyncConnect("127.0.0.1", 6379); if (c->err) { /* Let *c leak for now... */ printf("Error: %s\n", c->errstr); return 1; } redisLibeventAttach(c, base); redisAsyncSetConnectCallback(c, connectCallback); redisAsyncSetDisconnectCallback(c, disconnectCallback); redisAsyncCommand(c, NULL, NULL, "SET key %b", argv[argc - 1], strlen(argv[argc - 1])); redisAsyncCommand(c, getCallback, (char*) "end-1", "GET key"); redisAsyncCommand(c, getCallback, (char*) "end-1", "SUBSCRIBE foo"); Now how to tell hiredis to wait for message on channel ?

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