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• Advice using leaks in instruments for noobs

  - by Gyozo Kudor

  Hello I am pretty new to iphone development. I have run my app for the first time using the "Leaks" from "Instruments". It shows me several leaks around 20 the smallest is 32 bytes and there is one with 1KB. I have followed the memory management guidelines, (i (think i) understand how and when to use release, not to use it when adding to autorelease pools, for every copy, retain, init there should be a release,... etc). I don't think I understand the output of the Leaks in instruments. What does "Responsible library" and "Responsible frame" mean. Because there are some classes and methods i never used directly. Are there any good tutorials for debugging memory leaks in instruments or other advice you can give me regarding leaks. Thanks in advance. Here are the largest 2 leaks. Leaked Object # Address Size Responsible Library Responsible Frame Malloc 1.00 KB 0x4827400 1024 CFNetwork std::vector *, std::allocator * ::reserve(unsigned long) // i have no idea what this is. Leaked Object # Address Size Responsible Library Responsible Frame Malloc 128 Bytes 5 640 UIKit UIImagePickerLoadPhotoLibraryIfNecessary // so this means UIImagePicker is leaking memory? The first leak i get Leaked Object # Address Size Responsible Library Responsible Frame Malloc 128 Bytes 0x442dfd0 128 UIKit UIKeyboardInputManagerClassForInputMode I don't understand any of those.

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• Declaring struct in header file

  - by wrongusername

  I've been trying to include a structure called "student" in a student.h file, but I'm not quite sure how to do it. My student.h file code consists of entirely: #include<string> using namespace std; struct Student; while the student.cpp file consists of entirely: #include<string> using namespace std; struct Student { string lastName, firstName; //long list of other strings... just strings though }; Unfortunately, files that use #include "student.h" come up with numerous errors like error C2027: use of undefined type 'Student', error C2079: 'newStudent' uses undefined struct 'Student' (where newStudent is a function with a Student parameter), and error C2228: left of '.lastName' must have class/struct/union. It appears the compiler (VC++) does not recognize struct Student from "student.h" or something? I have tried declaring the whole struct in "student.h", but it didn't help either. How can I declare struct Student in "student.h" so that I can just #include "student.h" and start using the struct? BTW, it seems there are no compiler errors in student.h...

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• Beginner question - Loop invariants (Specifically Ch.3 of "Accelerated C++")

  - by Owen

  Hi - as I said, a complete beginner question here. I'm currently working my way through "Accelerated C++" and just came across this in chapter 3: // invariant: // we have read count grades so far, and // sum is the sum of the first count grades while (cin >> x) { ++count; sum += x; } The authors follow this by explaining that the invariant needs special attention paid to it because when the input is read into the variable x, we will have read count+1 grades and thus the invariant will be untrue. Similarly, when we have incremented the counter, the variable sum will no longer be the sum of the last count grades (in case you hadn't guessed, it's the traditional program for calculating student marks). What I don't understand is why this matters. Surely for just about any other loop, a similar statement would be true? For example, here is the book's first while loop (the output is filled in later): // invariant: we have written r rows so far while (r != rows) { // write a row of output std::cout << std::endl; ++r; } Once we have written the appropriate row of output, surely the invariant is false until we have incremented r, just as in the other example? It's probably something really obvious, anyone could enlighten me as to what makes these two cases different, that'd be great - and thanks in advance for taking the time to answer such a complete novice question. Owen

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• Multiple sendto() using UDP socket

  - by ereOn

  Hi, I have a network software which uses UDP to communicate with other instances of the same program. For different reasons, I must use UDP here. I recently had problems sending huge ammounts of data over UDP and had to implement a fragmentation system to split my messages into small data chunks. So far, it worked well but I now encounter an issue when I have to send a lot of data chunks. I have the following algorithm: Split message into small data chunks (around 1500 bytes) Iterate over the data chunks list and for each, send it using sendto() However, when I send a lot of data chunks, the receiver only gets the first 6 messages. Sometimes it misses the sixth and receives the seventh. It depends. Anyway, sendto() always indicates success. This always happen when I test my software over a loopback interface (127.0.0.1) but never over my LAN network. If I add something like std::cout << "test" << std::endl; between the sendto() then every frame is received. I am aware that UDP allows packet loss and that my frames might be loss for a lot of reasons and I suppose it has to do with the rate I am sending the data chunks at. What would be the right approach here ? Implementing some acknowledgement mechanism (just like TCP) seems overkill. Adding some arbitrary waiting time between the sendto() is ugly and will probably decrease performance. Increasing (if possible) the receiver UDP internal buffer ? I don't even know if this is possible. Something else ? I really need your advices here. Thank very much.

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• Extracting bool from istream in a templated function

  - by Thomas Matthews

  I'm converting my fields class read functions into one template function. I have field classes for int, unsigned int, long, and unsigned long. These all use the same method for extracting a value from an istringstream (only the types change): template <typename Value_Type> Value_Type Extract_Value(const std::string& input_string) { std::istringstream m_string_stream; m_string_stream.str(input_string); m_string_stream.clear(); m_string_stream >> value; return; } The tricky part is with the bool (Boolean) type. There are many textual representations for Boolean: 0, 1, T, F, TRUE, FALSE, and all the case insensitive combinations Here's the questions: What does the C++ standard say are valid data to extract a bool, using the stream extraction operator? Since Boolean can be represented by text, does this involve locales? Is this platform dependent? I would like to simplify my code by not writing my own handler for bool input. I am using MS Visual Studio 2008 (version 9), C++, and Windows XP and Vista.

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• C++ stack in Objective-C++

  - by helixed

  I'd like to use a C++ stack type in Objective-C, but I'm running into some issues. Here's a sample of what I would like to do: #import <stack> #import <UIKit/UIKit.h> @interface A : NSObject { stack<SEL> selectorStack; } @end Unfortunately, this doesn't compile. After messing around with the code for a while and trying different things, I can't seem to find a way to accomplish this. Can somebody tell me the best way to use a C++ stack within an Objective-C object or if it's even possible? Thanks. UPDATE: Well, KennyTM's answer worked on my example file, but for some reason when I tried to rename the class it quit working. Here's the code I have right now: #import <stack> #import <UIKit/UIKit.h> @interface MenuLayer : NSObject { std::stack<SEL> selectorStack; } @end The compiler spits out the following errors: stack: No such file or directory expected specifier-qualifier-list before 'std'

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• How can I change the precision of printing with the stl?

  - by mmr

  This might be a repeat, but my google-fu failed to find it. I want to print numbers to a file using the stl with the number of decimal places, rather than overall precision. So, if I do this: int precision = 16; std::vector<double> thePoint(3); thePoint[0] = 86.3671436; thePoint[0] = -334.8866574; thePoint[0] = 24.2814; ofstream file1(tempFileName, ios::trunc); file1 << std::setprecision(precision) << thePoint[0] << "\\" << thePoint[1] << "\\" << thePoint[2] << "\\"; I'll get numbers like this: 86.36714359999999\-334.8866574\24.28140258789063 What I want is this: 86.37\-334.89\24.28 In other words, truncating at two decimal points. If I set precision to be 4, then I'll get 86.37\-334.9\24.28 ie, the second number is improperly truncated. I do not want to have to manipulate each number explicitly to get the truncation, especially because I seem to be getting the occasional 9 repeating or 0000000001 or something like that that's left behind. I'm sure there's something obvious, like using the printf(%.2f) or something like that, but I'm unsure how to mix that with the stl << and ofstream.

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• Boost Thread Synchronization

  - by Dave18

  I don't see synchronized output when i comment the the line wait(1) in thread(). can I make them run at the same time (one after another) without having to use 'wait(1)'? #include <boost/thread.hpp> #include <iostream> void wait(int seconds) { boost::this_thread::sleep(boost::posix_time::seconds(seconds)); } boost::mutex mutex; void thread() { for (int i = 0; i < 100; ++i) { wait(1); mutex.lock(); std::cout << "Thread " << boost::this_thread::get_id() << ": " << i << std::endl; mutex.unlock(); } } int main() { boost::thread t1(thread); boost::thread t2(thread); t1.join(); t2.join(); }

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• How to loop through a boost::mpl::list?

  - by Kyle

  This is as far as I've gotten, #include <boost/mpl/list.hpp> #include <algorithm> namespace mpl = boost::mpl; class RunAround {}; class HopUpAndDown {}; class Sleep {}; template<typename Instructions> int doThis(); template<> int doThis<RunAround>() { /* run run run.. */ return 3; } template<> int doThis<HopUpAndDown>() { /* hop hop hop.. */ return 2; } template<> int doThis<Sleep>() { /* zzz.. */ return -2; } int main() { typedef mpl::list<RunAround, HopUpAndDown, Sleep> acts; // std::for_each(mpl::begin<acts>::type, mpl::end<acts>::type, doThis<????>); return 0; }; How do I complete this? (I don't know if I should be using std::for_each, just a guess based on another answer here)

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• When does invoking a member function on a null instance result in undefined behavior?

  - by GMan

  This question arose in the comments of a now-deleted answer to this other question. Our question was asked in the comments by STingRaySC as: Where exactly do we invoke UB? Is it calling a member function through an invalid pointer? Or is it calling a member function that accesses member data through an invalid pointer? With the answer deleted I figured we might as well make it it's own question. Consider the following code: #include <iostream> struct foo { void bar(void) { std::cout << "gman was here" << std::endl; } void baz(void) { x = 5; } int x; }; int main(void) { foo* f = 0; f->bar(); // (a) f->baz(); // (b) } We expect (b) to crash, because there is no corresponding member x for the null pointer. In practice, (a) doesn't crash because the this pointer is never used. Because (b) dereferences the this pointer (this->x = 5;), and this is null, the program enters undefined behavior. Does (a) result in undefined behavior? What about if both functions are static?

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• Compilation error while compiling an existing code base

  - by brijesh

  Hi, While building an existing code base on Mac OS using its native build setup I am getting some basic strange error while compilation phase. /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/bits/locale_facets.h: In constructor 'std::collate_byname<_CharT::collate_byname(const char*, size_t)': /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/bits/locale_facets.h:1072: error: '_M_c_locale_collate' was not declared in this scope /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/ppc-darwin/bits/messages_members.h: In constructor 'std::messages_byname<_CharT::messages_byname(const char*, size_t)': /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/ppc-darwin/bits/messages_members.h:79: error: '_M_c_locale_messages' was not declared in this scope /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits: At global scope: /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:897: error: 'float __builtin_huge_valf()' cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:897: error: a function call cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:897: error: 'float __builtin_huge_valf()' cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:897: error: a function call cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:899: error: 'float __builtin_nanf(const char*)' cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:899: error: a function call cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:899: error: 'float __builtin_nanf(const char*)' cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:899: error: a function call cannot appear in a constant-expression /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:900: error: field initializer is not constant /Developer/SDKs/MacOSX10.3.9.sdk/usr/include/gcc/darwin/3.3/c++/limits:915: error: field initializer is not constant

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• Where to find algorithms for standard math functions?

  - by dsimcha

  I'm looking to submit a patch to the D programming language standard library that will allow much of std.math to be evaluated at compile time using the compile-time function evaluation facilities of the language. Compile-time function evaluation has several limitations, the most important ones being: You can't use assembly language. You can't call C code or code for which the source is otherwise unavailable. Several std.math functions violate these and compile-time versions need to be written. Where can I get information on good algorithms for computing things such as logarithms, exponents, powers, and trig functions? I prefer just high level descriptions of algorithms to actual code, for two reasons: To avoid legal ambiguity and the need to make my code look "different enough" from the source to make sure I own the copyright. I want simple, portable algorithms. I don't care about micro-optimization as long as they're at least asymptotically efficient. Edit: D's compile time function evaluation model allows floating point results computed at compile time to differ from those computed at runtime anyhow, so I don't care if my compile-time algorithms don't give exactly the same result as the runtime version as long as they aren't less accurate to a practically significant extent.

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• Good hash function for a 2d index

  - by rlbond

  I have a struct called Point. Point is pretty simple: struct Point { Row row; Column column; // some other code for addition and subtraction of points is there too } Row and Column are basically glorified ints, but I got sick of accidentally transposing the input arguments to functions and gave them each a wrapper class. Right now I use a set of points, but repeated lookups are really slowing things down. I want to switch to an unordered_set. So, I want to have an unordered_set of Points. Typically this set might contain, for example, every point on a 80x24 terminal = 1920 points. I need a good hash function. I just came up with the following: struct PointHash : public std::unary_function<Point, std::size_t> { result_type operator()(const argument_type& val) const { return val.row.value() * 1000 + val.col.value(); } }; However, I'm not sure that this is really a good hash function. I wanted something fast, since I need to do many lookups very quickly. Is there a better hash function I can use, or is this OK?

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• Output iterator's value_type

  - by wilhelmtell

  The STL commonly defines an output iterator like so: template<class Cont> class insert_iterator : public iterator<output_iterator_tag,void,void,void,void> { // ... Why do output iterators define value_type as void? It would be useful for an algorithm to know what type of value it is supposed to output. For example, a function that translates a URL query "key1=value1&key2=value2&key3=value3" into any container that holds key-value strings elements. template<typename Ch,typename Tr,typename Out> void parse(const std::basic_string<Ch,Tr>& str, Out result) { std::basic_string<Ch,Tr> key, value; // loop over str, parse into p ... *result = typename iterator_traits<Out>::value_type(key, value); } The SGI reference page of value_type hints this is because it's not possible to dereference an output iterator. But that's not the only use of value_type: I might want to instantiate one in order to assign it to the iterator.

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• D callbacks in C functions

  - by Caspin

  I am writing D2 bindings for Lua. This is in one of the Lua header files. typedef int (*lua_CFunction) (lua_State *L); I assume the equivalent D2 statement would be: extern(C) alias int function( lua_State* L ) lua_CFunction; Lua also provides an api function: void lua_pushcfunction( lua_State* L, string name, lua_CFunction func ); If I want to push a D2 function does it have to be extern(C) or can I just use the function? int dfunc( lua_State* L ) { std.stdio.writeln("dfunc"); } extern(C) int cfunc( lua_State* L ) { std.stdio.writeln("cfunc"); } lua_State* L = lua_newstate(); lua_pushcfunction(L, "cfunc", &cfunc); //This will definitely work. lua_pushcfunction(L, "dfunc", &dfunc); //Will this work? If I can only use cfunc, why? I don't need to do anything like that in C++. I can just pass the address of a C++ function to C and everything just works.

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• Problem creating socket with C++ in winsock2

  - by Ash85

  Hi, I'm having the weirdest problem causing me headaches. Consider the following code: // Create and bind socket std::map<Connection, bool> clients; unsigned short port=6222; struct sockaddr_in local_address, from_address; int result; char buffer[10000]; SOCKET receive_socket; local_address.sin_family = AF_INET; local_address.sin_addr.s_addr = INADDR_ANY; local_address.sin_port = htons(port); receive_socket = socket(AF_INET,SOCK_DGRAM,0); What's happening is receive_socket is not binding, I get SOCKET_ERROR. When I debug the program and check receive_socket, it appears to just be garbled crap. I put a breakpoint on the 'std::map' line. When I step into each line of the above code, the debug cursor jumps straight from the 'unsigned short port' line to the first 'local_address.sin' line, even though I am using step into (F11), it does not stop at struct, int, char or SOCKET lines, it jumps straight over them. At this point I hover my mouse over local_address, from_address, result, buffer and receive_socket. They are all full of garbled crap. Is this because I have not defined these variables yet? I've also noticed that when I reach the bottom of the above code, local_address.sin_port is set to 19992, but it should be 6222?

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• stdexcept On Android

  - by David R.

  I'm trying to compile SoundTouch on Android. I started with this configure line: ./configure CPPFLAGS="-I/Volumes/android-build/mydroid/development/ndk/build/platforms/android-3/arch-arm/usr/include/" LDFLAGS="-Wl,-rpath-link=/Volumes/android-build/mydroid/development/ndk/build/platforms/android-3/arch-arm/usr/lib -L/Volumes/android-build/mydroid/development/ndk/build/platforms/android-3/arch-arm/usr/lib -nostdlib -lc" --host=arm-eabi --enable-shared=yes CFLAGS="-nostdlib -O3 -mandroid" host_alias=arm-eabi --no-create --no-recursion Because the Android NDK targets ARM, I also had to change the Makefile to remove the -msse2 flags to progress. When I run 'make', I get: /bin/sh ../../libtool --tag=CXX --mode=compile arm-eabi-g++ -DHAVE_CONFIG_H -I. -I../../include -I../../include -I/Volumes/android-build/mydroid/development/ndk/build/platforms/android-3/arch-arm/usr/include/ -O3 -fcheck-new -I../../include -g -O2 -MT FIRFilter.lo -MD -MP -MF .deps/FIRFilter.Tpo -c -o FIRFilter.lo FIRFilter.cpp libtool: compile: arm-eabi-g++ -DHAVE_CONFIG_H -I. -I../../include -I../../include -I/Volumes/android-build/mydroid/development/ndk/build/platforms/android-3/arch-arm/usr/include/ -O3 -fcheck-new -I../../include -g -O2 -MT FIRFilter.lo -MD -MP -MF .deps/FIRFilter.Tpo -c FIRFilter.cpp -o FIRFilter.o FIRFilter.cpp:46:21: error: stdexcept: No such file or directory FIRFilter.cpp: In member function 'virtual void soundtouch::FIRFilter::setCoefficients(const soundtouch::SAMPLETYPE*, uint, uint)': FIRFilter.cpp:177: error: 'runtime_error' is not a member of 'std' FIRFilter.cpp: In static member function 'static void* soundtouch::FIRFilter::operator new(size_t)': FIRFilter.cpp:225: error: 'runtime_error' is not a member of 'std' make[2]: *** [FIRFilter.lo] Error 1 make[1]: *** [all-recursive] Error 1 make: *** [all-recursive] Error 1 This isn't very surprising, since the -nostdlib flag was required. Android seems to have neither stdexcept nor stdlib. How can I get past this block of compiling SoundTouch? At a guess, there may be some flag I don't know about that I should use. I could refactor the code not to use stdexcept. There may be a way to pull in the original stdexcept source and reference that. I might be able to link to a precompiled stdexcept library.

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• Problem Linking Boost Filesystem Library in Microsoft Visual C++

  - by Scott

  Hello. I am having trouble getting my project to link to the Boost (version 1.37.0) Filesystem lib file in Microsoft Visual C++ 2008 Express Edition. The Filesystem library is not a header-only library. I have been following the Getting Started on Windows guide posted on the official boost web page. Here are the steps I have taken: I used bjam to build the complete set of lib files using: bjam --build-dir="C:\Program Files\boost\build-boost" --toolset=msvc --build-type=complete I copied the /libs directory (located in C:\Program Files\boost\build-boost\boost\bin.v2) to C:\Program Files\boost\boost_1_37_0\libs. In Visual C++, under Project Properties Additional Library Directories I added these paths: C:\Program Files\boost\boost_1_37_0\libs C:\Program Files\boost\boost_1_37_0\libs\filesystem\build\msvc-9.0express\debug\link-static\threading-multi I added the second one out of desperation. It is the exact directory where libboost_system-vc90-mt-gd-1_37.lib resides. In Configuration Properties C/C++ General Additional Include Directories I added the following path: C:\Program Files\boost\boost_1_37_0 Then, to put the icing on the cake, under Tools Options VC++ Directories Library files, I added the same directories mentioned in step 3. Despite all this, when I build my project I get the following error: fatal error LNK1104: cannot open file 'libboost_system-vc90-mt-gd-1_37.lib' Additionally, here is the code that I am attempting to compile as well as a screen shot of the aformentioned directory where the (assumedly correct) lib file resides: #include "boost/filesystem.hpp" // includes all needed Boost.Filesystem declarations #include <iostream> // for std::cout using boost::filesystem; // for ease of tutorial presentation; // a namespace alias is preferred practice in real code using namespace std; int main() { cout << "Hello, world!" << endl; return 0; } Can anyone help me out? Let me know if you need to know anything else. As always, thanks in advance.

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• opengl color quadrangle

  - by Tyzak

  hello i try out opengl. i have a programm that creates a black border an white corner (quadrangle). now i want to make the corner of the quadrangle in an different color. i don't know where exactly to write the code, and i don't know much a but color4f, i searcherd on google, but didn't get it. (is there a good description somewhere?) #include <iostream> #include <GL/freeglut.h> void Init() { glColor4f(100,0,0,0); } void RenderScene() //Zeichenfunktion { glLoadIdentity (); glBegin( GL_POLYGON ); glVertex3f( -0.5, -0.5, -0.5 ); glVertex3f( 0.5, -0.5, -0.5 ); glVertex3f( 0.5, 0.5, -0.5 ); glVertex3f( -0.5, 0.5, -0.5 ); glEnd(); glFlush(); } void Reshape(int width,int height) { } void Animate (int value) { std::cout << "value=" << value << std::endl; glutPostRedisplay(); glutTimerFunc(100, Animate, ++value); } int main(int argc, char **argv) { glutInit( &argc, argv ); // GLUT initialisieren glutInitDisplayMode( GLUT_RGB ); // Fenster-Konfiguration glutInitWindowSize( 600, 600 ); glutCreateWindow( "inkrement screen; visual screen" ); // Fenster-Erzeugung glutDisplayFunc( RenderScene ); // Zeichenfunktion bekannt machen glutReshapeFunc( Reshape ); glutTimerFunc( 10, Animate, 0); Init(); glutMainLoop(); return 0; }

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• Common practice for higher-order-polymorphism in scala

  - by raichoo

  Hi, I'm trying to grasp higher-order-polymophism in scala by implementing a very basic interface that describes a monad but I come across a problem that I don't really understand. I implemented the same with C++ and the code looks like this: #include <iostream> template <typename T> class Value { private: T value; public: Value(const T& t) { this->value = t; } T get() { return this->value; } }; template < template <typename> class Container > class Monad { public: template <typename A> Container<A> pure(const A& a); }; template <template <typename> class Container> template <typename A> Container<A> Monad<Container>::pure(const A& a) { return Container<A>(a); } int main() { Monad<Value> m; std::cout << m.pure(1).get() << std::endl; return 0; } When trying to do the same with scala I fail: class Value[T](val value: T) class Monad[Container[T]] { def pure[A](a: A): Container[A] = Container[A](a) } object Main { def main(args: Array[String]): Unit = { val m = new Monad[Value] m.pure(1) } } The compiler complains about: [raichoo@lain:Scala]:434> scalac highorder.scala highorder.scala:5: error: not found: value Container Container[A](a) ^ one error found What am I doing wrong here? There seems to be a fundamental concept I don't seem to understand about scala typeconstructors. Regards, raichoo

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• string Comparison

  - by muhammad-aslam

  I want to compare two user input strings, but not able to do so... #include "stdafx.h" #include "iostream" #include "string" using namespace std; int _tmain(int argc, _TCHAR* argv0[]) { string my_string; string my_string2; cout<<"Enter string"<<endl; cin>>my_string; cout<<"Enter 2nd string"<<endl; cin>>my_string2; cout<<my_string<<" "<<my_string2; strcmp(my_string,my_string2); int result; result= strcmp(my_string,my_string2); cout<<result<<endl; return 0; } This error is appearing. Error 1 error C2664: 'strcmp' : cannot convert parameter 1 from 'std::string' to 'const char *' c:\users\asad\documents\visual studio 2008\projects\string\string\string.cpp 23 String

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• Returning recursive ternary freaks out

  - by David Titarenco

  Hi, assume this following function: int binaryTree::findHeight(node *n) { if (n == NULL) { return 0; } else { return 1 + max(findHeight(n->left), findHeight(n->right)); } } Pretty standard recursive treeHeight function for a given binary search tree binaryTree. Now, I was helping a friend (he's taking an algorithms course), and I ran into some weird issue with this function that I couldn't 100% explain to him. With max being defined as max(a,b) ((a)>(b)?(a):(b)) (which happens to be the max definition in windef.h), the recursive function freaks out (it runs something like n^n times where n is the tree height). This obviously makes checking the height of a tree with 3000 elements take very, very long. However, if max is defined via templating, like std does it, everything is okay. So using std::max fixed his problem. I just want to know why. Also, why does the countLeaves function work fine, using the same programmatic recursion? int binaryTree::countLeaves(node *n) { if (n == NULL) { return 0; } else if (n->left == NULL && n->right == NULL) { return 1; } else { return countLeaves(n->left) + countLeaves(n->right); } } Is it because in returning the ternary function, the values a => countLeaves(n->left) and b => countLeaves(n->right) were recursively double called simply because they were the resultants? Thank you!

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• Can a destructor be recursive?

  - by Cubbi

  Is this program well-defined, and if not, why exactly? #include <iostream> #include <new> struct X { int cnt; X (int i) : cnt(i) {} ~X() { std::cout << "destructor called, cnt=" << cnt << std::endl; if ( cnt-- > 0 ) this->X::~X(); // explicit recursive call to dtor } }; int main() { char* buf = new char[sizeof(X)]; X* p = new(buf) X(7); p->X::~X(); // explicit call to dtor delete[] buf; } My reasoning: although invoking a destructor twice is undefined behavior, per 12.4/14, what it says exactly is this: the behavior is undefined if the destructor is invoked for an object whose lifetime has ended Which does not seem to prohibit recursive calls. While the destructor for an object is executing, the object's lifetime has not yet ended, thus it's not UB to invoke the destructor again. On the other hand, 12.4/6 says: After executing the body [...] a destructor for class X calls the destructors for X's direct members, the destructors for X's direct base classes [...] which means that after the return from a recursive invocation of a destructor, all member and base class destructors will have been called, and calling them again when returning to the previous level of recursion would be UB. Therefore, a class with no base and only POD members can have a recursive destructor without UB. Am I right?

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• why does b'(and sometimes b' ') show up when I split some HTML source[Python]

  - by Oliver

  I'm fairly new to Python and programming in general. I have done a few tutorials and am about 2/3 through a pretty good book. That being said I've been trying to get more comfortable with Python and proggramming by just trying things in the std lib out. that being said I have recently run into a wierd quirk that I'm sure is the result of my own incorrect or un-"pythonic" use of the urllib module(with Python 3.2.2) import urllib.request HTML_source = urllib.request.urlopen(www.somelink.com).read() print(HTML_source) when this bit is run through the active interpreter it returns the HTML source of somelink, however it prefixes it with b' for example b'<HTML>\r\n<HEAD> (etc). . . . if I split the string into a list by whitespace it prefixes every item with the b' I'm not really trying to accomplish something specific just trying to familiarize myself with the std lib. I would like to know why this b' is getting prefixed also bonus -- Is there a better way to get HTML source WITHOUT using a third party module. I know all that jazz about not reinventing the wheel and what not but I'm trying to learn by "building my own tools" Thanks in Advance!

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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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