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• Prolog .. Can i convert from a list of chars to a string or term in Prolog !!

  - by AhmadAssaf

  i use read_line_to_codes(Stream,Line) to read a line from a file .. first is there any way to read a line and assign it to a term in prolog ?? if not i managed to read a line and put it in this char list .. now this char list contains spaces .. which is bad .. so i want to convert it to a term or a string in prolog so that i can process it easier .. spaces cannot be atoms so thats a problem .. i appreciate the help !!

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• About the String#substring() method

  - by alain.janinm

  If we take a look at the String#substring method implementation : new String(offset + beginIndex, endIndex - beginIndex, value); We see that a new String is created with the same original content (parameter char [] value). So the workaround is to use new String(toto.substring(...)) to drop the reference to the original char[] value and make it eligible for GC (if no more references exist). I would like to know if there is a special reason that explain this implementation. Why the method doesn't create herself the new shorter String and why she keeps the full original value instead? The other related question is : should we always use new String(...) when dealing with substring?

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• a nicer way to create structs in a loop

  - by sandra

  Hi guys, I haven't coded in C++ in ages. And recently, I'm trying to work on something involving structs. Like this typedef struct{ int x; int y; } Point; Then in a loop, I'm trying to create new structs and put pointers to them them in a list. Point* p; int i, j; while (condition){ // compute values for i and j with some function... p = new Point; p* = {i, j}; //initialize my struct. list.append(p); //append this pointer to my list. } Now, my question is it possible to simplify this? I mean, the pointer variable *p outside of the loop and calling p = new Point inside the loop. Isn't there a better/nicer syntax for this?

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• How to extract img src, title and alt from html using php?

  - by Sam

  I would like to create a page where all images which reside on my website are listed with title and alternative representation. I already wrote me a little program to find and load all html files, but now I am stuck at how to extract src, title and alt from the html < img src="/image/fluffybunny.jpg" title="Harvey the bunny" alt="a cute little fluffy bunny"/ I guess this should be done with some regex, but since the order of the tags may vary, and I need all of them, I don't really know how to parse this in an elegant way (I could do it the hard char by char way, but thats painful).

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• Unmanaged C++ instantiation question

  - by Jim Jones

  Want to verify that my understanding of how this works. Have an unmanaged C++ Class with one public instance variable: char* character_encoding; and whose only constructor is defined as: TF_StringList(const char* encoding = "cp_1252"); when I use this class in either managed or unmanaged C++, the first thing I do is declare a pointer to an object of this class: const TF_StringList * categories; Then later I instantiate it: categories = new TF_StringList(); this gives me a pointer to an object of type TF_StringList whose variable character_encoding is set to "cp_1252"; So, is all that logic valid? Jim

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• NSNotifications vs delegate for multiple instances of same protocol

  - by Brent Traut

  I could use some architectural advice. I've run into the following problem a few times now and I've never found a truly elegant way to solve it. The issue, described at the highest level possible:I have a parent class that would like to act as the delegate for multiple children (all using the same protocol), but when the children call methods on the parent, the parent no longer knows which child is making the call. I would like to use loose coupling (delegates/protocols or notifications) rather than direct calls. I don't need multiple handlers, so notifications seem like they might be overkill. To illustrate the problem, let me try a super-simplified example: I start with a parent view controller (and corresponding view). I create three child views and insert each of them into the parent view. I would like the parent view controller to be notified whenever the user touches one of the children. There are a few options to notify the parent: Define a protocol. The parent implements the protocol and sets itself as the delegate to each of the children. When the user touches a child view, its view controller calls its delegate (the parent). In this case, the parent is notified that a view is touched, but it doesn't know which one. Not good enough. Same as #1, but define the methods in the protocol to also pass some sort of identifier. When the child tells its delegate that it was touched, it also passes a pointer to itself. This way, the parent know exactly which view was touched. It just seems really strange for an object to pass a reference to itself. Use NSNotifications. The parent defines a separate method for each of the three children and then subscribes to the "viewWasTouched" notification for each of the three children as the notification sender. The children don't need to attach themselves to the user dictionary, but they do need to send the notification with a pointer to themselves as the scope. Same as #4, but rather than using separate methods, the parent could just use one with a switch case or other branching along with the notification's sender to determine which path to take. Create multiple man-in-the-middle classes that act as the delegates to the child views and then call methods on the parent either with a pointer to the child or with some other differentiating factor. This approach doesn't seem scalable. Are any of these approaches considered best practice? I can't say for sure, but it feels like I'm missing something more obvious/elegant.

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• Operator Overloading for Queue C++

  - by Josh

  I was trying to use the overload operator method to copy the entries of one queue into another, but I am going wrong with my function. I don't know how else to access the values of the queue "original" any other way than what I have below: struct Node { int item; Node* next; }; class Queue { public: [...] //Extra code here void operator = (const Queue &original); protected: Node *front, *end; } void Queue::operator=(const Queue &original) { //THIS IS WHERE IM GOING WRONG while(original.front->next != NULL) { front->item = original.front->item; front->next = new Node; front = front->next; original.front = original.front->next; } }

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• C++ catch constructor exception

  - by aaa

  hi. I do not seem to understand how to catch constructor exception. Here is relevant code: struct Thread { rysq::cuda::Fock fock_; template<class iterator> Thread(const rysq::cuda::Centers &centers, const iterator (&blocks)[4]) : fock_() { if (!fock_) throw; } }; Thread *ct; try { ct = new Thread(centers_, blocks); } catch(...) { return false; } // catch never happens, So catch statement do not execute and I get unhandled exception. What did I do wrong? this is straight C++ using g++.

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• Why is comparing against "end()" iterator legal?

  - by sharptooth

  According to C++ standard (3.7.3.2/4) using (not only dereferencing, but also copying, casting, whatever else) an invalid pointer is undefined behavior (in case of doubt also see this question). Now the typical code to traverse an STL containter looks like this: std::vector<int> toTraverse; //populate the vector for( std::vector<int>::iterator it = toTraverse.begin(); it != toTraverse.end(); ++it ) { //process( *it ); } std::vector::end() is an iterator onto the hypothetic element beyond the last element of the containter. There's no element there, therefore using a pointer through that iterator is undefined behavior. Now how does the != end() work then? I mean in order to do the comparison an iterator needs to be constructed wrapping an invalid address and then that invalid address will have to be used in a comparison which again is undefined behavior. Is such comparison legal and why?

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• Using sscanf to parse two strings out

  - by Jessica

  I have a semi xml formatted file that contains line with the following format: <param name="Distance" value="1000Km" /> The first char in the string is usually a TAB or spaces. I've been using the following to try to parse the two strings out (from name and value): if(sscanf(lineread, "\t<param name=\"%s\" value=\"%s\" />", name, value) == 1) { //do something } name and value are char* Now, the result is always the same: name gets parse (I need to remove the quotes) and name is always empty. What am I doing wrong? Thanks, code is appreciated. Jess.

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• Storing a NTFS Security Descriptor in C

  - by Doori Bar

  My goal is to store a NTFS Security Descriptor in its identical native state. The purpose is to restore it on-demand. I managed to write the code for that purpose, I was wondering if anybody mind to validate a sample of it? (The for loop represents the way I store the native descriptor) This sample only contains the flag for "OWNER", but my intention is to apply the same method for all of the security descriptor flags. I'm just a beginner, would appreciate the heads up. Thanks, Doori Bar #define _WIN32_WINNT 0x0501 #define WINVER 0x0501 #include <stdio.h> #include <windows.h> #include "accctrl.h" #include "aclapi.h" #include "sddl.h" int main (void) { DWORD lasterror; PSECURITY_DESCRIPTOR PSecurityD1, PSecurityD2; HANDLE hFile; PSID owner; LPTSTR ownerstr; BOOL ownerdefault; int ret = 0; unsigned int i; hFile = CreateFile("c:\\boot.ini", GENERIC_READ | ACCESS_SYSTEM_SECURITY, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL); if (hFile == INVALID_HANDLE_VALUE) { fprintf(stderr,"CreateFile() failed. Error: INVALID_HANDLE_VALUE\n"); return 1; } lasterror = GetSecurityInfo(hFile, SE_FILE_OBJECT, OWNER_SECURITY_INFORMATION , &owner, NULL, NULL, NULL, &PSecurityD1); if (lasterror != ERROR_SUCCESS) { fprintf(stderr,"GetSecurityInfo() failed. Error: %lu;\n", lasterror); ret = 1; goto ret1; } ConvertSidToStringSid(owner,&ownerstr); printf("ownerstr of PSecurityD1: %s\n", ownerstr); /* The for loop represents the way I store the native descriptor */ PSecurityD2 = malloc( GetSecurityDescriptorLength(PSecurityD1) * sizeof(unsigned char) ); for (i=0; i < GetSecurityDescriptorLength(PSecurityD1); i++) ((unsigned char *) PSecurityD2)[i] = ((unsigned char *) PSecurityD1)[i]; if (IsValidSecurityDescriptor(PSecurityD2) == 0) { fprintf(stderr,"IsValidSecurityDescriptor(PSecurityD2) failed.\n"); ret = 2; goto ret2; } if (GetSecurityDescriptorOwner(PSecurityD2,&owner,&ownerdefault) == 0) { fprintf(stderr,"GetSecurityDescriptorOwner() failed."); ret = 2; goto ret2; } ConvertSidToStringSid(owner,&ownerstr); printf("ownerstr of PSecurityD2: %s\n", ownerstr); ret2: free(owner); free(ownerstr); free(PSecurityD1); free(PSecurityD2); ret1: CloseHandle(hFile); return ret; }

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• C++ String tokenisation from 3D .obj files

  - by Ben

  I'm pretty new to C++ and was looking for a good way to pull the data out of this line. A sample line that I might need to tokenise is f 11/65/11 16/70/16 17/69/17 I have a tokenisation method that splits strings into a vector as delimited by a string which may be useful static void Tokenise(const string& str, vector<string>& tokens, const string& delimiters = " ") The only way I can think of doing it is to tokenise with " " as a delimiter, remove the first item from the resulting vector, then tokenise each part by itself. Is there a good way to do this all in one?

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• C++ linked list based tree structure. Sanely move nodes between lists.

  - by krunk

  The requirements: Each Node in the list must contain a reference to its previous sibling Each Node in the list must contain a reference to its next sibling Each Node may have a list of child nodes Each child Node must have a reference to its parent node Basically what we have is a tree structure of arbitrary depth and length. Something like: -root(NULL) --Node1 ----ChildNode1 ------ChildOfChild --------AnotherChild ----ChildNode2 --Node2 ----ChildNode1 ------ChildOfChild ----ChildNode2 ------ChildOfChild --Node3 ----ChildNode1 ----ChildNode2 Given any individual node, you need to be able to either traverse its siblings. the children, or up the tree to the root node. A Node ends up looking something like this: class Node { Node* previoius; Node* next; Node* child; Node* parent; } I have a container class that stores these and provides STL iterators. It performs your typical linked list accessors. So insertAfter looks like: void insertAfter(Node* after, Node* newNode) { Node* next = after->next; after->next = newNode; newNode->previous = after; next->previous = newNode; newNode->next = next; newNode->parent = after->parent; } That's the setup, now for the question. How would one move a node (and its children etc) to another list without leaving the previous list dangling? For example, if Node* myNode exists in ListOne and I want to append it to listTwo. Using pointers, listOne is left with a hole in its list since the next and previous pointers are changed. One solution is pass by value of the appended Node. So our insertAfter method would become: void insertAfter(Node* after, Node newNode); This seems like an awkward syntax. Another option is doing the copying internally, so you'd have: void insertAfter(Node* after, const Node* newNode) { Node *new_node = new Node(*newNode); Node* next = after->next; after->next = new_node; new_node->previous = after; next->previous = new_node; new_node->next = next; new_node->parent = after->parent; } Finally, you might create a moveNode method for moving and prevent raw insertion or appending of a node that already has been assigned siblings and parents. // default pointer value is 0 in constructor and a operator bool(..) // is defined for the Node bool isInList(const Node* node) const { return (node->previous || node->next || node->parent); } // then in insertAfter and friends if(isInList(newNode) // throw some error and bail I thought I'd toss this out there and see what folks came up with.

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• In a binary search Tree

  - by user1044800

  In a binary search tree that takes a simple object.....when creating the getter and setter methods for the left, right, and parent. do I a do a null pointer? as in this=this or do I create the object in each method? Code bellow... This is my code: public void setParent(Person parent) { parent = new Person( parent.getName(), parent.getWeight()); //or is the parent supposed to be a null pointer ???? This is the code it came from: public void setParent(Node parent) { this.parent = parent; } Their code takes a node from the node class...my set parent is taking a person object from my person class.....

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• Error message in XSLT with C# extension function

  - by iHeartGreek

  Hi! I am received the following error while trying to implement a C# extension function in XSLT. Extension function parameters or return values which have CLR type 'Char[]' are not supported.** code: <xsl:variable name="stringList"> <xsl:value-of select="extension:GetList('AAA BBB CCC', ' ')"/> </xsl:variable> <msxsl:script language="C#" implements-prefix="extension"> <![CDATA[ public string[] GetList(string str, char[] delimiter) { ... ... return str.Split(delimiter, StringSplitOptions.None); } ]]> </msxsl:script> Can someone explain this error message and how to get past it? Thanks!

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• Store address dynamic array in c

  - by user280642

  I'm trying to save the address of a dynamic array index. struct sstor *dlist; struct node *q; q->item = &(dlist->item[(dlist->sz)-1]); // Problem? This is my node struct node { char **item; struct node *next; struct node *prev; }; This is my array struct sstor { int sz; int maxsz; char item[][1024]; }; I'm still new to pointers. The line below gives the error: assignment from incompatible pointer type q->item = &(dlist->item[(dlist->sz)-1]);

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• Somewhat newb question about assy and the heap.

  - by Eric M

  Ultimately I am just trying to figure out how to dynamically allocate heap memory from within assembly. If I call Linux sbrk() from assembly code, can I use the address returned as I would use an address of a statically (ie in the .data section of my program listing) declared chunk of memory? I know Linux uses the hardware MMU if present, so I am not sure if what sbrk returns is a 'raw' pointer to real RAM, or is it a cooked pointer to RAM that may be modified by Linux's VM system? I read this: How are sbrk/brk implemented in Linux?. I suspect I can not use the return value from sbrk() without worry: the MMU fault on access-non-allocated-address must cause the VM to alter the real location in RAM being addressed. Thus assy, not linked against libc or what-have-you, would not know the address has changed. Does this make sense, or am I out to lunch?

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• Making uppercase of std::string

  - by Daniel K.

  Which implementation do you think is better? std::string ToUpper( const std::string& source ) { std::string result; result.reserve( source.length() ); std::transform( source.begin(), source.end(), result.begin(), std::ptr_fun<int, int>( std::toupper ) ); return result; } and... std::string ToUpper( const std::string& source ) { std::string result( source.length(), '\0' ); std::transform( source.begin(), source.end(), result.begin(), std::ptr_fun<int, int>( std::toupper ) ); return result; } Difference is that the first one uses reserve method after the default constructor, but the second one uses the constructor accepting the number of characters.

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• template typename question

  - by stephenteh

  Hi, I have a problem with template and wondering is there a possible way to achieve what I wanted to do. Here is my question. template <typename T> class A { public: typedef T* pointer; typedef const pointer const_pointer; A() {} template <typename D> A(const D& d) { // how can I store the D type // so I can refer it later on // outside of this function } };

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• Boost::asio bug in MSVC10 - Failing BOOST_WORKAROUND in ~buffer_debug_check() in buffer.hpp

  - by shaz

  A straight compilation of example http://www.boost.org/doc/libs/1_43_0/doc/html/boost_asio/tutorial/tutdaytime3/src.html results in a runtime null pointer exception. Stack trace points to the buffer_debug_check destructor which contains this comment: // MSVC's string iterator checking may crash in a std::string::iterator // object's destructor when the iterator points to an already-destroyed // std::string object, unless the iterator is cleared first. The test #if BOOST_WORKAROUND(BOOST_MSVC, = 1400) succeeds in MSVC10 and (but) results in a null pointer exception in c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xutility line 123 _Iterator_base12& operator=(const _Iterator_base12& _Right) { // assign an iterator if (_Myproxy != _Right._Myproxy) _Adopt(_Right._Myproxy->_Mycont); return (*this); } _Right._Myproxy is NULL

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• Why do I get corrupt output on my file?

  - by Martin

  I have a simple program which I have compiled in both MinGW and Visual C++ 2008 Express, and both give an output file larger than 88200. When I set s = 0, both programs work as expected. What am I doing wrong? #include <fstream> using namespace std; int main(int argc, char *argv[]) { int i; short s; fstream f; f.open("test.raw", ios_base::out); for(i = 0; i < 44100; i++) { s = i & 0xFFFF; // PROBLEM? f.write(reinterpret_cast<const char *>(&s), sizeof(s)); } f.close(); return 0; }

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• Codesample with bufferoverflow (gets method). Why does it not behave as expected?

  - by citronas

  This an extract from an c program that should demonstrate a bufferoverflow. void foo() { char arr[8]; printf(" enter bla bla bla"); gets(arr); printf(" you entered %s\n", arr); } The question was "How many input chars can a user maximal enter without a creating a buffer overflow" My initial answer was 8, because the char-array is 8 bytes long. Although I was pretty certain my answer was correct, I tried a higher amount of chars, and found that the limit of chars that I can enter, before I get a segmentation fault is 11. (Im running this on A VirtualBox Ubuntu) So my question is: Why is it possible to enter 11 chars into that 8 byte array?

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• Is concatenating with an empty string to do a string conversion really that bad?

  - by polygenelubricants

  Let's say I have two char variables, and later on I want to concatenate them into a string. This is how I would do it: char c1, c2; // ... String s = "" + c1 + c2; I've seen people who say that the "" + "trick" is "ugly", etc, and that you should use String.valueOf or Character.toString instead. I prefer this construct because: I prefer using language feature instead of API call if possible In general, isn't the language usually more stable than the API? If language feature only hides API call, then even stronger reason to prefer it! More abstract! Hiding is good! I like that the c1 and c2 are visually on the same level String.valueOf(c1) + c2 suggests something is special about c1 It's shorter. Is there really a good argument why String.valueOf or Character.toString is preferrable to "" +? Trivia: in java.lang.AssertionError, the following line appears 7 times, each with a different type: this("" + detailMessage);

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• test cases for testing a strtok-alike function [C++]

  - by Neeraj

  Consider the following class definition: class StrToTokens { StrToTokens(const char* str, const char* delimiters = "\t\r\n"); //constructor string getNextToken(); void reset(); bool empty(); } Can someone list some good testcases to test the above class. A few I could think of are: empty string, empty delimiters, repeated delimiters, consecutive delimiters, string with only delimiters. However, the interviewer expected some more(better ones). Can you help out. Thanks.

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• Perfect Forwarding to async lambda

  - by Alexander Kondratskiy

  I have a function template, where I want to do perfect forwarding into a lambda that I run on another thread. Here is a minimal test case which you can directly compile: #include <thread> #include <future> #include <utility> #include <iostream> #include <vector> /** * Function template that does perfect forwarding to a lambda inside an * async call (or at least tries to). I want both instantiations of the * function to work (one for lvalue references T&, and rvalue reference T&&). * However, I cannot get the code to compile when calling it with an lvalue. * See main() below. */ template <typename T> std::string accessValueAsync(T&& obj) { std::future<std::string> fut = std::async(std::launch::async, [](T&& vec) mutable { return vec[0]; }, std::forward<T>(obj)); return fut.get(); } int main(int argc, char const *argv[]) { std::vector<std::string> lvalue{"Testing"}; // calling with what I assume is an lvalue reference does NOT compile std::cout << accessValueAsync(lvalue) << std::endl; // calling with rvalue reference compiles std::cout << accessValueAsync(std::move(lvalue)) << std::endl; // I want both to compile. return 0; } For the non-compiling case, here is the last line of the error message which is intelligible: main.cpp|13 col 29| note: no known conversion for argument 1 from ‘std::vector<std::basic_string<char> >’ to ‘std::vector<std::basic_string<char> >&’ I have a feeling it may have something to do with how T&& is deduced, but I can't pinpoint the exact point of failure and fix it. Any suggestions? Thank you! EDIT: I am using gcc 4.7.0 just in case this could be a compiler issue (probably not)

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