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  • C++ STL: Trouble with string iterators

    - by Rosarch
    I'm making a simple command line Hangman game. void Hangman::printStatus() { cout << "Lives remaining: " << livesRemaining << endl; cout << getFormattedAnswer() << endl; } string Hangman::getFormattedAnswer() { return getFormattedAnswerFrom(correctAnswer.begin(), correctAnswer.end()); } string Hangman::getFormattedAnswerFrom(string::const_iterator begin, string::const_iterator end) { return begin == end? "" : displayChar(*begin) + getFormattedAnswerFrom(++begin, end); } char Hangman::displayChar(const char c) { return c; } (Eventually, I'll change this so displayChar() displays a - or a character if the user has guessed it, but for simplicity now I'm just returning everything.) When I build and run this from VS 2010, I get a popup box: Debug Assertion Failed! xstring Line: 78 Expression: string iterator not dereferenceable What am I doing wrong?

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  • Adapting Map Iterators Using STL/Boost/Lambdas

    - by John Dibling
    Consider the following non-working code: typedef map<int, unsigned> mymap; mymap m; for( int i = 1; i < 5; ++i ) m[i] = i; // 'remove' all elements from map where .second < 3 remove(m.begin(), m.end(), bind2nd(less<int>(), 3)); I'm trying to remove elements from this map where .second < 3. This obviously isn't written correctly. How do I write this correctly using: Standard STL function objects & techniques Boost.Bind C++0x Lambdas I know I'm not eraseing the elements. Don't worry about that; I'm just simplifying the problem to solve.

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  • C++ STL: Trouble with iterators

    - by Rosarch
    I'm having a beginner problem: bool _isPalindrome(const string& str) { return _isPalindrome(str.begin(), str.end()); // won't compile } bool _isPalindrome(string::iterator begin, string::iterator end) { return begin == end || *begin == *end && _isPalindrome(++begin, --end); } What am I doing wrong here? Why doesn't str.begin() get type checked to be a string::iterator?

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  • Correct way of setting a custom FileInfo class to an Iterator

    - by Gordon
    I am trying to set a custom class to an Iterator through the setInfoClass method: Use this method to set a custom class which will be used when getFileInfo and getPathInfo are called. The class name passed to this method must be derived from SplFileInfo. My class is like this (simplified example): class MyFileInfo extends SplFileInfo { public $props = array( 'foo' => '1', 'bar' => '2' ); } The iterator code is this: $rit = new RecursiveIteratorIterator( new RecursiveDirectoryIterator('/some/file/path/'), RecursiveIteratorIterator::SELF_FIRST); Since RecursiveDirectoryIterator is by inheritance through DirectoryIterator also an SplFileInfo object, it provides the setInfoClass method (it's not listed in the manual, but reflection shows it's there). Thus I can do: $rit->getInnerIterator()->setInfoClass('MyFileInfo'); All good up to here, but when iterating over the directory with foreach($rit as $file) { var_dump( $file ); } I get the following weird result object(MyFileInfo)#4 (3) { ["props"]=>UNKNOWN:0 ["pathName":"SplFileInfo":private]=>string(49) "/some/file/path/someFile.txt" ["fileName":"SplFileInfo":private]=>string(25) "someFile.txt" } So while MyFileInfo is picked up, I cannot access it's properties. If I add custom methods, I can invoke them fine, but any properties are UNKNOWN. If I don't set the info class to the iterator, but to the SplFileInfo object (like shown in the example in the manual), it will give the same UNKNOWN result: foreach($rit as $file) { // $file is a SplFileInfo instance $file->setInfoClass('MyFileInfo'); var_dump( $file->getFileInfo() ); } However, it will work when I do foreach($rit as $file) { $file = new MyFileInfo($file); var_dump( $file ); } Unfortunately, the code I a want to use this in is somewhat more complicated and stacks some more iterators. Creating the MyFileInfo class like this is not an option. So, does anyone know how to get this working or why PHP behaves this weird? Thanks.

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  • Usage of setInfoClass() on DirectoryIterator vs on RecursiveDirectoryIterator

    - by Gordon
    I've ran into an inconsistent behavior when using setInfoClass to set a custom SplFileInfo class to a DirectoryIterator versus setting it to a RecursiveIterator. The method description states: Use this method to set a custom class which will be used when getFileInfo and getPathInfo are called. The class name passed to this method must be derived from SplFileInfo. Consider this custom SplFileInfo class A extends SplFileInfo { public function test() { printf("I am of class %s\n", __CLASS__); } } and my iterators $iterator = new DirectoryIterator('.'); and $iterator = new RecursiveDirectoryIterator('.'); Now I'd expect those two to behave the same when I do $iterator->setInfoClass('A'); foreach($iterator as $file) { $file->test(); } and output 'I am of A' for each $file encountered and in fact, the RecursiveDirectoryIterator will do that. But the DirectoryIterator will raise Fatal error: Call to undefined method DirectoryIterator::test() so apparently the InfoClass does not get applied when iterating over the files. At least not directly, because when I change the code in the foreach loop to $file->getPathInfo()->test(); it will work for the DirectoryIterator. But then the RecursiveDirectoryIterator will raise Fatal error: Call to undefined method SplFileInfo::test() Like I said, I'd expect those two to behave the same, but apparently getFileInfo and getPathInfo don't get called in the DirectoryIterator, which I consider a bug. So if there is any Iterator experts out there, please help me understand this. Thanks.

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  • syntax help required on templated static member function

    - by omatai
    I have a bunch of containers of object pointers that I want to iterate through in different contexts to produce diagnostics for them. I'm struggling with the syntax required to define the functions... which, on account of these objects filtering through diverse parts of my application, seem best encapsulated in a dedicated diagnostics class thus: // Code sketch only - detail fleshed out below... class ObjectListDiagnoser { public: static void GenerateDiagnostics( /* help required here! */ ); }; ... // Elsewhere in the system... ObjectListDiagnoser::GenerateDiagnostics( /* help required here! */ ); What I'd like to be able to do (in places across my application) is at least this: std::vector<MyObject *> objGroup1; std::list<MyObject *> objGroup2; ObjectListDiagnoser::GenerateDiagnostics( objGroup1.begin(), objGroup1.end() ); ObjectListDiagnoser::GenerateDiagnostics( objGroup2.begin(), objGroup2.end() ); ObjectListDiagnoser::GenerateDiagnostics( objGroup1.rbegin(), objGroup1.rend() ); I have tried to template my function in two ways, with no success: class ObjectListDiagnoser { public: // 1 - nope. template <class ObjIter> static void GenerateDiagnostics( ObjIter first, ObjIter last ); // 2. - nope. template <class Container, class ObjIter> static void GenerateDiagnostics( Container<MyObject *>::ObjIter first, Container<MyObject *>::ObjIter last ); }; Can someone provide the correct syntax for this? The container type will vary, and the direction of iteration will vary, but always for the same type of object.

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  • Iterating backward

    - by MBennett
    Suppose I have a vector<int> myvec and I want to loop through all of the elements in reverse. I can think of a few ways of doing this: for (vector<int>::iterator it = myvec.end() - 1; it >= myvec.begin(); --it) { // do stuff here } for (vector<int>::reverse_iterator rit = myvec.rbegin(); rit != myvec.rend(); ++rit) { // do stuff here } for (int i = myvec.size() - 1; i >= 0; --i) { // do stuff here } So my question is when should I use each? Is there a difference? I know that the first one is dangerous because if I pass in an empty vector, then myvec.end() - 1 is undefined, but are there any other hazards or inefficiencies with this?

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  • std::list iterator: get next element

    - by sheepsimulator
    I'm trying to build a string using data elements stored in a std::list, where I want commas placed only between the elements (ie, if elements are {A,B,C,D} in list, result string should be "A,B,C,D". This code does not work: typedef std::list< shared_ptr<EventDataItem> > DataItemList; // ... std::string Compose(DataItemList& dilList) { std::stringstream ssDataSegment; for(iterItems = dilList.begin(); iterItems != dilList.end(); iterItems++) { // Lookahead in list to see if next element is end if((iterItems + 1) == dilList.end()) { ssDataSegment << (*iterItems)->ToString(); } else { ssDataSegment << (*iterItems)->ToString() << ","; } } return ssDataSegment.str(); } How do I get at "the-next-item" in a std::list using an iterator? I would expect that it's a linked-list, why can't I get at the next item?

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  • Is there a simple way to make lists behave as files (with ftplib)

    - by Brent.Longborough
    I'd like to use ftplib to upload program-generated data as lists. The nearest method I can see for doing this is ftp.storlines, but this requires a file object with a readlines() method. Obviously I could create a file, but this seems like overkill as the data isn't persistent. Is there anything that could do this?: session = ftp.new(...) upload = convertListToFileObject(mylist) session.storlines("STOR SOMETHING",upload) session.quit

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  • Python Beginner: Selective Printing in loops

    - by Jonathan Straus
    Hi there. I'm a very new python user (had only a little prior experience with html/javascript as far as programming goes), and was trying to find some ways to output only intermittent numbers in my loop for a basic bicycle racing simulation (10,000 lines of biker positions would be pretty excessive :P). I tried in this loop several 'reasonable' ways to communicate a condition where a floating point number equals its integer floor (int, floor division) to print out every 100 iterations or so: for i in range (0,10000): i = i + 1 t = t + t_step #t is initialized at 0 while t_step is set at .01 acceleration_rider1 = (power_rider1 / (70 * velocity_rider1)) - (force_drag1 / 70) velocity_rider1 = velocity_rider1 + (acceleration_rider1 * t_step) position_rider1 = position_rider1 + (velocity_rider1 * t_step) force_drag1 = area_rider1 * (velocity_rider1 ** 2) acceleration_rider2 = (power_rider2 / (70 * velocity_rider1)) - (force_drag2 / 70) velocity_rider2 = velocity_rider2 + (acceleration_rider2 * t_step) position_rider2 = position_rider2 + (velocity_rider2 * t_step) force_drag2 = area_rider1 * (velocity_rider2 ** 2) if t == int(t): #TRIED t == t // 1 AND OTHER VARIANTS THAT DON'T WORK HERE:( print t, "biker 1", position_rider1, "m", "\t", "biker 2", position_rider2, "m"

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  • std::list : get next element

    - by sheepsimulator
    I'm trying to build a string using data elements stored in a std::list, where I want commas placed only between the elements (ie, if elements are {A,B,C,D} in list, result string should be "A,B,C,D". This code does not work: typedef std::list< shared_ptr<EventDataItem> > DataItemList; // ... std::string Compose(DataItemList& dilList) { std::stringstream ssDataSegment; for(iterItems = dilList.begin(); iterItems = dilList.end(); iterItems++) { // Lookahead in list to see if next element is end if((iterItems + 1) == dilList.end()) { ssDataSegment << (*iterItems)->ToString(); } else { ssDataSegment << (*iterItems)->ToString() << ","; } } return ssDataSegment.str(); } How do I get at "the-next-item" in a std::list using an iterator? I would expect that it's a linked-list, why can't I get at the next item?

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  • Display `pretty output` of directory content from array

    - by user275074
    Hi, I'm using the following code to get an array of directories and their sub-directories where each contain file type extension: png. It works great but I need to be able to output the results of the array in a list style format e.g. Test - test2.png - test1.png subfolder - test3.png sub sub folder - test4.png etc Code: $filter=".png"; $directory='../test'; $it=new RecursiveDirectoryIterator("$directory"); foreach(new RecursiveIteratorIterator($it) as $file){ if(!((strpos(strtolower($file),$filter))===false)||empty($filter)){ $items[]=preg_replace("#\\\#", "/", $file); } } Example array of results: array ( 0 => '../test/test2.png', 1 => '../test/subfolder/subsubfolder/test3.png', 2 => '../test/subfolder/test3.png', 3 => '../test/test1.png', ) What would be the best way of achieving the desired result?

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  • List iterator not dereferencable?

    - by Roderick
    Hi All I get the error "list iterator not dereferencable" when using the following code: bool done = false; while (!_list_of_messages.empty() && !done) { // request the next message to create a frame // DEBUG ERROR WHEN NEXT LINE IS EXECUTED: Counted_message_reader reader = *(_list_of_messages.begin()); if (reader.has_more_data()) { _list_of_frames.push_back(new Dlp_data_frame(reader, _send_compressed_frames)); done = true; } else { _list_of_messages.pop_front(); } } (The line beginning with "Counted_message_reader..." is the one giving the problem) Note that the error doesn't always occur but seemingly at random times (usually when there's lots of buffered data). _list_of_messages is declared as follows: std::list<Counted_message_reader> _list_of_messages; In the surrounding code we could do pop_front, push_front and size, empty or end checks on _list_of_messages but no erase calls. I've studied the STL documentation and can't see any glaring problems. Is there something wrong with the above code or do I have a memory leak somewhere? Thanks! Appreciated!

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  • Iterator blocks and inheritance.

    - by Dave Van den Eynde
    Given a base class with the following interface: public class Base { public virtual IEnumerable<string> GetListOfStuff() { yield return "First"; yield return "Second"; yield return "Third"; } } I want to make a derived class that overrides the method, and adds its own stuff, like so: public class Derived : Base { public override IEnumerable<string> GetListOfStuff() { foreach (string s in base.GetListOfStuff()) { yield return s; } yield return "Fourth"; yield return "Fifth"; } } However, I'm greeted with a warning that "access to a member through a base keyword from an iterator cannot be verified". What's the accepted solution to this problem then?

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  • Is there a neater way to get the first occurrence of something?

    - by Phil H
    I have a list which contains a number of things: lista = ['a', 'b', 'foo', 'c', 'd', 'e', 'bar'] I'd like to get the first item in the list that fulfils a predicate, say len(item) > 2. Is there a neater way to do it than itertools' dropwhile and next? first = next(itertools.dropwhile(lambda x: len(x) <= 2, lista)) I did use [item for item in lista if len(item)>2][0] at first, but that requires python to generate the entire list first.

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  • Iterative Cartesian Product in Java

    - by akappa
    Hi, I want to compute the cartesian product of an arbitrary number of nonempty sets in Java. I've wrote that iterative code... public static <T> List<Set<T>> cartesianProduct(List<Set<T>> list) { List<Iterator<T>> iterators = new ArrayList<Iterator<T>>(list.size()); List<T> elements = new ArrayList<T>(list.size()); List<Set<T>> toRet = new ArrayList<Set<T>>(); for (int i = 0; i < list.size(); i++) { iterators.add(list.get(i).iterator()); elements.add(iterators.get(i).next()); } for (int j = 1; j >= 0;) { toRet.add(Sets.newHashSet(elements)); for (j = iterators.size()-1; j >= 0 && !iterators.get(j).hasNext(); j--) { iterators.set(j, list.get(j).iterator()); elements.set(j, iterators.get(j).next()); } elements.set(Math.abs(j), iterators.get(Math.abs(j)).next()); } return toRet; } ...but I found it rather inelegant. Someone has a better, still iterative solution? A solution that uses some wonderful functional-like approach? Otherwise... suggestion about how to improve it? Errors? Thanks :)

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  • C++ iterators, default initialization and what to use as an uninitialized sentinel.

    - by Hassan Syed
    The Context I have a custom template container class put together from a map and vector. The map resolves a string to an ordinal, and the vector resolves an ordinal (only an initial string to ordinal lookup is done, future references are to the vector) to the entry. The entries are modified intrusively to contain a a bool "assigned" and an iterator_type which is a const_iterator to the container class's map. My container class will use RCF's serialization code (which models boost::serialization) to serialize my container classes to nodes in a network. Serializing iterator's is not possible, or a can of worms, and I can easily regenerate them onces the vectors and maps are serialized on the remote site. The Question I need to default initialize, and be able to test that the iterator has not been assigned to (if it is assigned it is valid, if not it is invalid). Since map iterators are not invalidated upon operations performed on it (unless of course items are removed :D) am I to assume that map<x,y>::end() is a valid sentinel (regardless of the state of the map -- i.e., it could be empty) to initialize to ? I will always have access to the parent map, I'm just unsure wheather end() is the same as the map contents change. I don't want to use another level of indirection (--i.e., boost::optional) to achieve my goal, I'd rather forego compiler checks to correct logic, but it would be nice if I didn't need to. Misc This question exists, but most of its content seems non-sense. Assigning a NULL to an iterator is invalid according to g++ and clang++. This is another similar question, but it focuses on the common use-cases of iterators, which generally tends to be using the iterator to iterate, ofcourse in this use-case the state of the container isn't meant to change whilst iteration is going on.

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  • Are there any C# collections where modification does not invalidate iterators?

    - by young-phillip
    Are there any data structures in the C# Collections library where modification of the structure does not invalidate iterators? Consider the following: List<int> myList = new List<int>(); myList.Add( 1 ); myList.Add( 2 ); List<int>.Enumerator myIter = myList.GetEnumerator(); myIter.MoveNext(); // myIter.Current == 1 myList.Add( 3 ); myIter.MoveNext(); // throws InvalidOperationException

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  • Deleting elements from stl set while iterating through it does not invalidate the iterators.

    - by pedromanoel
    I need to go through a set and remove elements that meet a predefined criteria. This is the test code I wrote: #include <set> #include <algorithm> void printElement(int value) { std::cout << value << " "; } int main() { int initNum[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }; std::set<int> numbers(initNum, initNum + 10); // print '0 1 2 3 4 5 6 7 8 9' std::for_each(numbers.begin(), numbers.end(), printElement); std::set<int>::iterator it = numbers.begin(); // iterate through the set and erase all even numbers for (; it != numbers.end(); ++it) { int n = *it; if (n % 2 == 0) { // wouldn't invalidate the iterator? numbers.erase(it); } } // print '1 3 5 7 9' std::for_each(numbers.begin(), numbers.end(), printElement); return 0; } At first, I thought that erasing an element from the set while iterating through it would invalidate the iterator, and the increment at the for loop would have undefined behavior. Even though, I executed this test code and all went well, and I can't explain why. My question: Is this the defined behavior for std sets or is this implementation specific? I am using gcc 4.3.3 on ubuntu 10.04 (32-bit version), by the way. Thanks!

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  • String vectors not working as expected with newline and iterators? (C++)

    - by kevin
    I have a text file made of 3 lines: Line 1 Line 3 (Line 1, a blank line, and Line 3) vector<string> text; vector<string>::iterator it; ifstream file("test.txt"); string str; while (getline(file, str)) { if (str.length() == 0) str = "\n"; // since getline discards the newline character, replacing blank strings with newline text.push_back(str); } // while for (it=text.begin(); it < text.end(); it++) cout << (*it); Prints out: Line 1 Line 3 I'm not sure why the string with only a newline was not printed out. Any help would be appreciated. Thanks.

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  • Does operator precedence in C++ differ for pointers and iterators?

    - by oraz
    The code below demonstrates this difference: #include <iostream> #include <string> int main() { char s[] = "ABCD"; std::string str(s); char *p = s; while(*p) { *p++ = tolower(*p); // <-- incr after assignment } std::cout << s << std::endl; std::string::iterator it = str.begin(), end = str.end(); while(it != end) { *it++ = tolower(*it); // <-- incr before assignment ? } std::cout << str << std::endl; return 0; } the code above outputs: abcd bcd if we separate assignment operation and increment operator: while(it != end) { *it = tolower(*it); // <-- incr before assignment ? it++; } the output will be as expected. What's wrong with the original code? $ g++ --version g++ (GCC) 3.4.4 (cygming special, gdc 0.12, using dmd 0.125) Copyright (C) 2004 Free Software Foundation, Inc.

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  • How to check whether iterators form a contiguous memory zone?

    - by Vincent
    I currently have the following function to read an array or a vector of raw data (_readStream is a std::ifstream) : template<typename IteratorType> inline bool MyClass::readRawData( const IteratorType& first, const IteratorType& last, typename std::iterator_traits<IteratorType>::iterator_category* = nullptr ) { _readStream.read(reinterpret_cast<char*>(&*first), (last-first)*sizeof(*first)); return _readStream.good(); } First question : does this function seem ok for you ? As we read directly a block of memory, it will only work if the memory block from first to last is contiguous in memory. How to check that ?

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  • How can I have a Foo* iterator to a vector of Foo?

    - by mghie
    If I have a class that contains a std::list<Foo>, how can I implement iterators to a Foo* collection, preferably without using boost? I'd rather not maintain a parallel collection of pointers. For now I have std::list<Foo>, mostly so that removing or inserting an element does not invalidate all other iterators, but would it be possible to implement other iterators too, so that the collection type used in the implementation is opaque to the user of the class?

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