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• The Definitive C++ Book Guide and List

  - by grepsedawk

  After more than a few questions about deciding on C++ books I thought we could make a better community wiki version. Providing QUALITY books and an approximate skill level. Maybe we can add a short blurb/description about each book that you have personally read / benefited from. Feel free to debate quality, headings, etc. Note: There is a similar post for C: The Definitive C Book Guide and List Reference Style - All Levels The C++ Programming Language - Bjarne Stroustrup C++ Standard Library Tutorial and Reference - Nicolai Josuttis Beginner Introductory: C++ Primer - Stanley Lippman / Josée Lajoie / Barbara E. Moo Accelerated C++ - Andrew Koenig / Barbara Moo Thinking in C++ - Bruce Eckel (2 volumes, 2nd is more about standard library, but still very good) Best practices: Effective C++ - Scott Meyers Effective STL - Scott Meyers Intermediate More Effective C++ - Scott Meyers Exceptional C++ - Herb Sutter More Exceptional C++ - Herb Sutter C++ Coding Standards: 101 Rules, Guidelines, and Best Practices - Herb Sutter / Andrei Alexandrescu C++ Templates The Complete Guide - David Vandevoorde / Nicolai M. Josuttis Large Scale C++ Software Design - John Lakos Above Intermediate Modern C++ Design - Andrei Alexandrescu C++ Template Metaprogramming - David Abrahams and Aleksey Gurtovoy Inside the C++ Object Model - Stanley Lippman Classics / Older Note: Some information contained within these books may not be up to date and no longer considered best practice. The Design and Evolution of C++ - Bjarne Stroustrup Ruminations on C++ Andrew Koenig / Barbara Moo Advanced C++ Programming Styles and Idioms - James Coplien

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• Why does this class declaration not work on Visual Studio

  - by Roel

  So I'm trying to get some code that is written for gcc to compile on Visual Studio 2008. I have a problem that I have narrowed down to this: class value_t { public: typedef std::deque<value_t> sequence_t; typedef sequence_t::iterator iterator; }; This code fails: 1>cpptest.cpp 1>c:\program files\microsoft visual studio 9.0\vc\include\deque(518) : error C2027: use of undefined type 'value_t' 1> c:\temp\cpptest\cpptest.cpp(10) : see declaration of 'value_t' 1> c:\temp\cpptest\cpptest.cpp(13) : see reference to class template instantiation 'std::deque<_Ty>' being compiled 1> with 1> [ 1> _Ty=value_t 1> ] 1>c:\program files\microsoft visual studio 9.0\vc\include\deque(518) : error C2027: use of undefined type 'value_t' 1> c:\temp\cpptest\cpptest.cpp(10) : see declaration of 'value_t' However when I try this with std::vector, it compiles fine: class value_t { public: typedef std::vector<value_t> sequence_t; typedef sequence_t::iterator iterator; }; What's wrong? I have tried adding 'typename' everywhere I can think of, but at this point in time I'm thinking it's just a bug in the Dinkumware STL. Can anyone explain what's happening, and/or offer a solution? Thanks.

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• Nested instances in C#

  - by user32848

  I'm trying to translate some C++ code for a neural net into C#. I first took the C++ code, from a 1993 book, and ran it. Then translated it using the STL and it ran again. Now I'm trying to get it into C# with Visual Web Developer 2008 Express. The original code used "friend" classes and I'm just trying to do the same making everything "public". The following code compiles but only gives null references when run: public class ineuron { public Double weight, activation; public ineuron(Double set_wt) { weight = set_wt; } ... public class netwrk { public oneuron onrn; public ineuron in1, in2, in3, in4; public netwrk( Double inp_1, Double inp_2, Double inp_3, Double inp_4 ) { ineuron in1 = new ineuron(inp_1); ineuron in2 = new ineuron(inp_2); ... and later, in some code called by a button push: netwrk ntw = new netwrk(i_n1, i_n2, i_n3, i_n4); Unfortunately, trying to use: ntw.in1.activation etc. leads to null reference runtime errors. What am I forgetting to do? Barney

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• Statically Compiling QWebKit 4.6.2

  - by geeko

  I tried to compile Qt+Webkit statically with MS VS 2008 and this worked. C:\Qt\4.6.2configure -release -static -opensource -no-fast -no-exceptions -no-accessibility -no-rtti -no-stl -no-opengl -no-openvg -no-incredibuild-xge -no-style-plastique -no-style-cleanlooks -no-style-motif -no-style-cde -no-style-windowsce -no-style-windowsmobile -no-style-s60 -no-gif -no-libpng -no-libtiff -no-libjpeg -no-libmng -no-qt3support -no-mmx -no-3dnow -no-sse -no-sse2 -no-iwmmxt -no-openssl -no-dbus -platform win32-msvc2008 -arch windows -no-phonon -no-phonon-backend -no-multimedia -no-audio-backend -no-script -no-scripttools -webkit -no-declarative However, I get these errors whenever building a project that links statically to QWebKit: 1 Creating library C:\Users\Geeko\Desktop\Qt\TestQ\Release\TestQ.lib and object C:\Users\Geeko\Desktop\Qt\TestQ\Release\TestQ.exp 1QtWebKit.lib(PluginPackageWin.obj) : error LNK2019: unresolved external symbol _VerQueryValueW@16 referenced in function "class WebCore::String __cdecl WebCore::getVersionInfo(void * const,class WebCore::String const &)" (?getVersionInfo@WebCore@@YA?AVString@1@QAXABV21@@Z) 1QtWebKit.lib(PluginPackageWin.obj) : error LNK2019: unresolved external symbol _GetFileVersionInfoW@16 referenced in function "private: bool __thiscall WebCore::PluginPackage::fetchInfo(void)" (?fetchInfo@PluginPackage@WebCore@@AAE_NXZ) 1QtWebKit.lib(PluginPackageWin.obj) : error LNK2019: unresolved external symbol _GetFileVersionInfoSizeW@8 referenced in function "private: bool __thiscall WebCore::PluginPackage::fetchInfo(void)" (?fetchInfo@PluginPackage@WebCore@@AAE_NXZ) 1QtWebKit.lib(PluginDatabaseWin.obj) : error LNK2019: unresolved external symbol _imp_PathRemoveFileSpecW@4 referenced in function "class WebCore::String __cdecl WebCore::safariPluginsDirectory(void)" (?safariPluginsDirectory@WebCore@@YA?AVString@1@XZ) 1QtWebKit.lib(PluginDatabaseWin.obj) : error LNK2019: unresolved external symbol _imp_SHGetValueW@24 referenced in function "void __cdecl WebCore::addWindowsMediaPlayerPluginDirectory(class WTF::Vector &)" (?addWindowsMediaPlayerPluginDirectory@WebCore@@YAXAAV?$Vector@VString@WebCore@@$0A@@WTF@@@Z) 1QtWebKit.lib(PluginDatabaseWin.obj) : error LNK2019: unresolved external symbol _imp_PathCombineW@12 referenced in function "void __cdecl WebCore::addMacromediaPluginDirectories(class WTF::Vector &)" (?addMacromediaPluginDirectories@WebCore@@YAXAAV?$Vector@VString@WebCore@@$0A@@WTF@@@Z) 1C:\Users\Geeko\Desktop\Qt\TestQ\Release\TestQ.exe : fatal error LNK1120: 6 unresolved externals Do I need to check something in the Qt project options ? I have QtCore, QtGui, Network and WebKit checked.

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• Statically Compiling Qt 4.6.2

  - by geeko

  This what I did but it results in errors: 1: In win32-msvc2008\qmake.conf I set QMAKE_CFLAGS_RELEASE = -O1 -Og -GL -MD 2: From MSVC2008 CMD I run vcvarsall.bat x86 and vcvars32.bat "C:\Program Files\Microsoft Visual Studio 9.0\VC\bin 3: From Qt 4.6.2 CMD I run the following C:\Qt\4.6.2configure -release -nomake examples -nomake demos -no-exceptions -n o-stl -no-rtti -no-qt3support -no-scripttools -no-openssl -no-opengl -no-webkit -no-phonon -no-style-motif -no-style-cde -no-style-cleanlooks -no-style-plastique -no-sql-sqlite -platform win32-msvc2008 -static -qt-libjpeg -qt-zlib -qt-libpng and then nmake However, I ended up every time with these errors: link /LIBPATH:"c:\Qt\4.6.2\lib" /LIBPATH:"c:\Qt\4.6.2\lib" /NOLOGO /INCR EMENTAL:NO /MANIFEST /MANIFESTFILE:"tmp\obj\release_static\assistant_adp.interme diate.manifest" /SUBSYSTEM:WINDOWS "/MANIFESTDEPENDENCY:type='win32' name='Micro soft.Windows.Common-Controls' version='6.0.0.0' publicKeyToken='6595b64144ccf1df ' language='' processorArchitecture=''" /OUT:......\bin\assistant_adp.exe @C :\DOCUME~1\Geeko\LOCALS~1\Temp\nm3F8.tmp fontpanel.obj : MSIL .netmodule or module compiled with /GL found; restarting li nk with /LTCG; add /LTCG to the link command line to improve linker performance main.obj : error LNK2001: unresolved external symbol "class QObject * __cdecl qt _plugin_instance_qjpeg(void)" (?qt_plugin_instance_qjpeg@@YAPAVQObject@@XZ) ......\bin\assistant_adp.exe : fatal error LNK1120: 1 unresolved externals NMAKE : fatal error U1077: '"C:\Program Files\Microsoft Visual Studio 9.0\VC\BIN \link.EXE"' : return code '0x460' Stop. NMAKE : fatal error U1077: '"C:\Program Files\Microsoft Visual Studio 9.0\VC\BIN \nmake.exe"' : return code '0x2' Stop. NMAKE : fatal error U1077: 'cd' : return code '0x2' Stop. NMAKE : fatal error U1077: 'cd' : return code '0x2' Stop. NMAKE : fatal error U1077: 'cd' : return code '0x2' Stop. Thank you in deed.

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• What Qt container class to use for a sorted list?

  - by Dave

  Part of my application involves rendering audio waveforms. The user will be able to zoom in/out of the waveform. Starting at fully zoomed-out, I only want to sample the audio at the necessary internals to draw the waveform at the given resolution. Then, when they zoom in, asynchronously resample the "missing points" and provide a clearer waveform. (Think Google Maps.) I'm not sure the best data structure to use in Qt world. Ideally, I would like to store data samples sorted by time, but with the ability to fill-in points as needed. So, for example, the data points might initially look like: data[0 ms] = 10 data[10 ms] = 32 data[20 ms] = 21 ... But when they zoom in, I would get more points as necessary, perhaps: data[0 ms] = 10 data[2 ms] = 11 data[4 ms] = 18 data[6 ms] = 30 data[10 ms] = 32 data[20 ms] = 21 ... Note that the values in brackets are lookup values (milliseconds), not array indices. In .Net I might have used a SortedList<int, int>. What would be the best class to use in Qt? Or should I use a STL container?

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• priority queue with limited space: looking for a good algorithm

  - by SigTerm

  This is not a homework. I'm using a small "priority queue" (implemented as array at the moment) for storing last N items with smallest value. This is a bit slow - O(N) item insertion time. Current implementation keeps track of largest item in array and discards any items that wouldn't fit into array, but I still would like to reduce number of operations further. looking for a priority queue algorithm that matches following requirements: queue can be implemented as array, which has fixed size and _cannot_ grow. Dynamic memory allocation during any queue operation is strictly forbidden. Anything that doesn't fit into array is discarded, but queue keeps all smallest elements ever encountered. O(log(N)) insertion time (i.e. adding element into queue should take up to O(log(N))). (optional) O(1) access for *largest* item in queue (queue stores *smallest* items, so the largest item will be discarded first and I'll need them to reduce number of operations) Easy to implement/understand. Ideally - something similar to binary search - once you understand it, you remember it forever. Elements need not to be sorted in any way. I just need to keep N smallest value ever encountered. When I'll need them, I'll access all of them at once. So technically it doesn't have to be a queue, I just need N last smallest values to be stored. I initially thought about using binary heaps (they can be easily implemented via arrays), but apparently they don't behave well when array can't grow anymore. Linked lists and arrays will require extra time for moving things around. stl priority queue grows and uses dynamic allocation (I may be wrong about it, though). So, any other ideas?

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• How to get rid of void-pointers.

  - by Patrick

  I inherited a big application that was originally written in C (but in the mean time a lot of C++ was also added to it). Because of historical reasons, the application contains a lot of void-pointers. Before you start to choke, let me explain why this was done. The application contains many different data structures, but they are stored in 'generic' containers. Nowadays I would use templated STL containers for it, or I would give all data structures a common base class, so that the container can store pointers to the base class, but in the [good?] old C days, the only solution was to cast the struct-pointer to a void-pointer. Additionally, there is a lot of code that works on these void-pointers, and uses very strange C constructions to emulate polymorphism in C. I am now reworking the application, and trying to get rid of the void-pointers. Adding a common base-class to all the data structures isn't that hard (few days of work), but the problem is that the code is full of constructions like shown below. This is an example of how data is stored: void storeData (int datatype, void *data); // function prototype ... Customer *myCustomer = ...; storeData (TYPE_CUSTOMER, myCustomer); This is an example of how data is fetched again: Customer *myCustomer = (Customer *) fetchData (int datatype, char *key); I actually want to replace all the void-pointers with some smart-pointer (reference-counted), but I can't find a trick to automate (or at least) help me to get rid of all the casts to and from void-pointers. Any tips on how to find, replace, or interact in any possible way with these conversions?

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• Flex 3: should I provide prepared data to my component or make it to process data before display?

  - by grapkulec

  I'm starting to learn a little Flex just for fun and maybe to prove that I still can learn something new :) I have some idea for a project and one of its parts is a tree component which could display data in different ways depending on configuration. The idea There is list of objects having properties like id, date, time, name, description. And sometimes list should be displayed like this: first level: date second level: time third level: name and sometimes like this: first level: year second level: month third level: day fourth level: time and name By level I mean level of nesting of course. So, we can have years, that have months, that have days, that have hours and so forth. The problem What could be the best way to do it? I mean, should I prepare data for different ways of nesting outside of component or even outside of flex? I can do it at web service level in C# where I plan to have database access layer and send to flex nice and ready to display XML or array of objects. But I wonder if that won't cause additional and maybe unneccessary network traffic. I tried to hack some code in my component to convert my data objects into XML or ArrayCollection but I don't know enough of Flex and got stuck on elimination of duplicates or getting specific data by some key value. Usually to do such things I have STL with maps, sets and vectors and I find Flex arrays and even Dictionary a little bit confusing (I've read language reference and googled without any significant luck). The question So, to sum things up: should I give my tree component data prepared just for chosen type of display or should I try to do it internally inside component (or some helper class written in ActionScript)?

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• C# style Action<T>, Func<T,T>, etc in C++0x

  - by Austin Hyde

  C# has generic function types such as Action<T> or Func<T,U,V,...> With the advent of C++0x and the ability to have template typedef's and variadic template parameters, it seems this should be possible. The obvious solution to me would be this: template <typename T> using Action<T> = void (*)(T); however, this does not accommodate for functors or C++0x lambdas, and beyond that, does not compile with the error "expected unqualified-id before 'using'" My next attempt was to perhaps use boost::function: template <typename T> using Action<T> = boost::function<void (T)>; This doesn't compile either, for the same reason. My only other idea would be STL style template arguments: template <typename T, typename Action> void foo(T value, Action f) { f(value); } But this doesn't provide a strongly typed solution, and is only relevant inside the templated function. Now, I will be the first to admit that I am not the C++ wiz I prefer to think I am, so it's very possible there is an obvious solution I'm not seeing. Is it possible to have C# style generic function types in C++?

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• How does the destructor know when to activate itself? Can it be relied upon?

  - by Robert Mason

  Say for example i have the following code (pure example): class a { int * p; public: a() { p = new int; ~a() { delete p; } }; a * returnnew() { a retval; return(&retval); } int main() { a * foo = returnnew(); return 0; } In returnnew(), would retval be destructed after the return of the function (when retval goes out of scope)? Or would it disable automatic destruction after i returned the address and i would be able to say delete foo; at the end of main()? Or, in a similar vein (pseudocode): void foo(void* arg) { bar = (a*)arg; //do stuff exit_thread(); } int main() { while(true) { a asdf; create_thread(foo, (void*)&asdf); } return 0; } where would the destructor go? where would i have to say delete? or is this undefined behavior? Would the only possible solution be to use the STL referenced-counted pointers? how would this be implemented? Thank you- i've used C++ for a while but never quite been in this type of situation, and don't want to create memory leaks.

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• Quickest algorithm for finding sets with high intersection

  - by conradlee

  I have a large number of user IDs (integers), potentially millions. These users all belong to various groups (sets of integers), such that there are on the order of 10 million groups. To simplify my example and get to the essence of it, let's assume that all groups contain 20 user IDs (i.e., all integer sets have a cardinality of 100). I want to find all pairs of integer sets that have an intersection of 15 or greater. Should I compare every pair of sets? (If I keep a data structure that maps userIDs to set membership, this would not be necessary.) What is the quickest way to do this? That is, what should my underlying data structure be for representing the integer sets? Sorted sets, unsorted---can hashing somehow help? And what algorithm should I use to compute set intersection)? I prefer answers that relate C/C++ (especially STL), but also any more general, algorithmic insights are welcome. Update Also, note that I will be running this in parallel in a shared memory environment, so ideas that cleanly extend to a parallel solution are preferred.

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• How can I apply a PSSM efficiently?

  - by flies

  I am fitting for position specific scoring matrices (PSSM aka Position Specific Weight Matrices). The fit I'm using is like simulated annealing, where I the perturb the PSSM, compare the prediction to experiment and accept the change if it improves agreement. This means I apply the PSSM millions of times per fit; performance is critical. In my particular problem, I'm applying a PSSM for an object of length L (~8 bp) at every position of a DNA sequence of length M (~30 bp) (so there are M-L+1 valid positions). I need an efficient algorithm to apply a PSSM. Can anyone help improve performance? My best idea is to convert the DNA into some kind of a matrix so that applying the PSSM is matrix multiplication. There are efficient linear algebra libraries out there (e.g. BLAS), but I'm not sure how best to turn an M-length DNA sequence into a matrix M x 4 matrix and then apply the PSSM at each position. The solution needs to work for higher order/dinucleotide terms in the PSSM - presumably this means representing the sequence-matrix for mono-nucleotides and separately for dinucleotides. My current solution iterates over each position m, then over each letter in word from m to m+L-1, adding the corresponding term in the matrix. I'm storing the matrix as a multi-dimensional STL vector, and profiling has revealed that a lot of the computation time is just accessing the elements of the PSSM (with similar performance bottlenecks accessing the DNA sequence). If someone has an idea besides matrix multiplication, I'm all ears.

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• COM-Objects containing maps / content error(0)

  - by Florian Berzsenyi

  I'm writing a small wrapper to get familiar with some important topics in C++ (WinAPI, COM, STL,OOP). For now, my class shall be able to create a (child) window. Mainly, this window is connected to a global message loop that distribute messages to a local loop of the right instance (global is static, local is virtual). Obviously, there are surely better ways to do that but I'm using std::maps to store HWND and their instance pointer in pairs (the Global loop looks for the pointer with the HWND-parameter, gets itself the pointer from the map and calls then the local loop). Now, it appears that the map does not accept any values because of a unknown reason. It seems to allocate enough space but something went wrong anyway [ (error) 0 is displayed instead of the entries in visual C++). I've looked that up in google as well and found out that maps cause some trouble when used in classes AND DLLs. May this be the reason and is there any solution?? Protected scope of class: static std::map<HWND,MAP_BASE_OBJECT*> m_LoopBuf Implementation in .cpp-file: std::map<HWND,MAP_BASE_OBJECT*> HWindow::m_LoopBuf;

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• Is there a Boost (or other common lib) type for matrices with string keys?

  - by mohawkjohn

  I have a dense matrix where the indices correspond to genes. While gene identifiers are often integers, they are not contiguous integers. They could be strings instead, too. I suppose I could use a boost sparse matrix of some sort with integer keys, and it wouldn't matter if they're contiguous. Or would this still occupy a great deal of space, particularly if some genes have identifiers that are nine digits? Further, I am concerned that sparse storage is not appropriate, since this is an all-by-all matrix (there will be a distance in each and every cell, provided the gene exists). I'm unlikely to need to perform any matrix operations (e.g., matrix multiplication). I will need to pull vectors out of the matrix (slices). It seems like the best type of matrix would be keyed by a Boost unordered_map (a hash map), or perhaps even simply an STL map. Am I looking at this the wrong way? Do I really need to roll my own? I thought I saw such a class somewhere before. Thanks!

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• structure inside structure - c++ Error

  - by gamadeus

  First of all the error I am getting is of the type: Request for member 's' of struct1.struct1::struct2, which is of non class type '__u32' where: struct struct1 { struct x struct2; struct x struct3; struct x struct4; }; The usage is of the form: struct struct1 st1; st1.struct2.s = Value; Now my struct1 is: struct ip_mreq_source { struct in_addr imr_multiaddr; struct in_addr imr_sourceaddr; struct in_addr imr_interface; }; struct 'x' is in_addr Where: typedef uint32_t in_addr_t; struct in_addr { in_addr_t s_addr; }; element 's' is the element s_addr in in_addr. My detailed error coming out of g++ (GCC 4.4.3) from the Android based compiler: arm-linux-androideabi-g++ -MMD -MP -MF groupsock/GroupsockHelper.o.d.org -fpic -ffunction-sections -funwind-tables -fstack-protector -D__ARM_ARCH_5__ -D__ARM_ARCH_5T__ -D__ARM_ARCH_5E__ -D__ARM_ARCH_5TE__ -Wno-psabi -march=armv5te -mtune=xscale -msoft-float -fno-exceptions -fno-rtti -mthumb -Os -fomit-frame-pointer -fno-strict-aliasing -finline- limit=64 -Igroupsock/include -Igroupsock/../UsageEnvironment/include -Iandroid- ndk-r5b/sources/cxx-stl/system/include -Igroupsock -DANDROID -Wa,--noexecstack -DANDROID_NDK -Wall -fexceptions -O2 -DNDEBUG -g -Iandroid-8/arch-arm/usr/include -c groupsock/GroupsockHelper.cpp -o groupsock/GroupsockHelper.o && rm -f groupsock/GroupsockHelper.o.d && mv groupsock/GroupsockHelper.o.d.org groupsock/GroupsockHelper.o.d groupsock/GroupsockHelper.cpp: In function 'Boolean socketJoinGroupSSM(UsageEnvironment&, int, netAddressBits, netAddressBits)': groupsock/GroupsockHelper.cpp:427: error: request for member 's_addr' in 'imr.ip_mreq_source::imr_multiaddr', which is of non-class type '__u32' groupsock/GroupsockHelper.cpp:428: error: request for member 's_addr' in 'imr.ip_mreq_source::imr_sourceaddr', which is of non-class type '__u32' groupsock/GroupsockHelper.cpp:429: error: request for member 's_addr' in 'imr.ip_mreq_source::imr_interface', which is of non-class type '__u32' I am not sure what is causing the error. Any pointers would be great - no pun intended. Thanks

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• Project Euler Problem #11

  - by SoulBeaver

  Source: http://projecteuler.net/index.php?section=problems&id=11 Quick overview: Take a 20x20 grid of numbers and compute the largest product of 4 pairs of numbers in either horizontal, vertical, or diagonal. My current approach is to divide the 20x20 grid up into single rows and single columns and go from there with a much more manageable grid. The code I'm using to divide the rows into rows is void fillRows ( string::const_iterator& fieldIter, list<int>& rowElements, vector<list<int>>& rows ) { int count(0); for( ; fieldIter < field.end(); ++fieldIter ) { if(isdigit(field[*fieldIter])) { rowElements.push_back(toInt(field[*fieldIter])); ++count; } if(count == 40) { rows.push_back(rowElements); count = 0; rowElements.clear(); } } } Short explanation: I have the field set as static const std::string field and I am filling a vector with lists of rows. Why a list? Because the queue doesn't have a clear function. Also practice using STL container lists and not ones I write myself. However, this thing isn't working. Oftentimes I see it omitting a character( function toInt parses the const char as int ) and I end up with 18 rows, two rows short of the 20x20 grid. The length of the rows seem good. Rows: 18 RowElements[0]: 40 (instead of pairs I saved each number individually. Will fix that later) What am I doing wrong?

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• How to implement escape Sequence in SDL

  - by Sa'me Smd

  Im trying to use the STL library inside the SDL. but it gives me the error "undeclared identifier" Is there any way i can use "\n"or even cout<<endl; Can the function SDL_WarpMousewhich places the mouse cursor on a desired location on screen help me with this. Because i want to put a tile on the next line sequence. I hope you get the Question. Its very vague and messed up question though (sorry for that). EDIT: void putMap(SDL_Surface* tile, SDL_Surface* screen) { for(int y = 0; y < 21; y++) { for(int x = 0; x < 60; x++) { if(maze[x][y] != '#') { apply_surface( x*10 , y*10 , tile, screen); } } cout<<endl; } } c:\documents and settings\administrator\my documents\visual studio 2008\projects\craptest\craptest\main.cpp(605) : error C2065: 'cout' : undeclared identifier c:\documents and settings\administrator\my documents\visual studio 2008\projects\craptest\craptest\main.cpp(605) : error C2065: 'endl' : undeclared identifier This is my apply_surface funtion. void apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination ) { //Make a temporary rectangle to hold the offsets SDL_Rect offset; //Give the offsets to the rectangle offset.x = x; offset.y = y; //Blit the surface SDL_BlitSurface( source, NULL, destination, &offset ); }

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• Some clarification needed about synchronous versus asynchronous asio operations

  - by Old newbie

  As far as I know, the main difference between synchronous and asynchronous operations. I.e. write() or read() vs async_write() and async_read() is that the former, don't return until the operation finish -or error-, and the last ones, returns inmediately. Due the fact that the asynchronous operations are controlled by an io_service.run() that does not finish until the controlled operations has finalized. It seems to me that in sequencial operations as those involved in TCP/IP connections with protocols such as POP3, in which the operaton is a sequence such as: C: <connect> S: Ok. C: User... S: Ok. C: Password S: Ok. C: Command S: answer C: Command S: answer ... C: bye S: <close> The difference between synchronous/asynchronous opperatons does not make much sense. Of course, in both operations there is allways the risk that the program flow stops indefinitely by some circunstance -there the use of timers-, but I would like know some more authorized opinions in this matter. I must admit that the question is rather ill-defined, but I like hear some advices about when use one or other, because I've problems in debugging with MS Visual Studio, asynchronous SSL operations in a POP3 client in wich I'm working now -about some of who surely I would write here soon-, and sometimes think that perhaps is a bad idea use asynchronous in this. Not to say that I'm an absolute newbie with this librarys, that additionally to the difficult with the idioma, and some obscure concepts in the STL, must suffer the brevity of the asio documentation.

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• Implementing list position locator in C++?

  - by jfrazier

  I am writing a basic Graph API in C++ (I know libraries already exist, but I am doing it for the practice/experience). The structure is basically that of an adjacency list representation. So there are Vertex objects and Edge objects, and the Graph class contains: list<Vertex *> vertexList list<Edge *> edgeList Each Edge object has two Vertex* members representing its endpoints, and each Vertex object has a list of Edge* members representing the edges incident to the Vertex. All this is quite standard, but here is my problem. I want to be able to implement deletion of Edges and Vertices in constant time, so for example each Vertex object should have a Locator member that points to the position of its Vertex* in the vertexList. The way I first implemented this was by saving a list::iterator, as follows: vertexList.push_back(v); v->locator = --vertexList.end(); Then if I need to delete this vertex later, then rather than searching the whole vertexList for its pointer, I can call: vertexList.erase(v->locator); This works fine at first, but it seems that if enough changes (deletions) are made to the list, the iterators will become out-of-date and I get all sorts of iterator errors at runtime. This seems strange for a linked list, because it doesn't seem like you should ever need to re-allocate the remaining members of the list after deletions, but maybe the STL does this to optimize by keeping memory somewhat contiguous? In any case, I would appreciate it if anyone has any insight as to why this happens. Is there a standard way in C++ to implement a locator that will keep track of an element's position in a list without becoming obsolete? Much thanks, Jeff

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• Wrapping unmanaged C++ with C++/CLI - a proper approach.

  - by Jamie

  Hi there, as stated in the title, I want to have my old C++ library working in managed .NET. I think of two possibilities: 1) I might try to compile the library with /clr and try "It Just Works" approach. 2) I might write a managed wrapper to the unmanaged library. First of all, I want to have my library working FAST, as it was in unmanaged environment. Thus, I am not sure if the first approach will not cause a large decrease in performance. However, it seems to be faster to implement (not a right word :-)) (assuming it will work for me). On the other hand, I think of some problems that might appear while writing a wrapper (e.g. how to wrap some STL collection (vector for instance)?) I think of writing a wrapper residing in the same project as the unmanaged C++ resides - is that a reasonable approach (e.g. MyUnmanagedClass and MyManagedClass in the same project, the second wrapping the other)? What would you suggest in that problem? Which solution is going to give me better performance of the resulting code? Thank you in advance for any suggestions and clues! Cheers

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• Link error for user defined class type template parameter

  - by isurulucky

  Hi, I implemented a Simple STL map in C++. Factored out the comparison as a type as I was instructed to, then implemented the comparison as shown below: template <typename T> int KeyCompare<T>::operator () (T tKey1, T tKey2) { if(tKey1 < tKey2) return -1; else if(tKey1 > tKey2) return 1; else return 0; } here, tKey1 and tKet2 are the two keys I'm comparing. This worked well for all the basic data types and string. I added a template specialization to compare keys of a user defined type named Test and added a specialization as follows: int KeyCompare<Test>::operator () (Test tKey1, Test tKey2) { if(tKey1.a < tKey2.a) return -1; else if(tKey1.a > tKey2.a) return 1; else return 0; } when I run this, I get a linking error saying SimpleMap.obj : error LNK2005: "public: int __thiscall KeyCompare::operator()(class Test,class Test)" (??R?$KeyCompare@VTest@@@@QAEHVTest@@0@Z) already defined in MapTest.obj SimpleMap.obj : error LNK2005: "public: __thiscall KeyCompare::~KeyCompare(void)" (??1?$KeyCompare@VTest@@@@QAE@XZ) already defined in MapTest.obj SimpleMap.obj : error LNK2005: "public: __thiscall KeyCompare::KeyCompare(void)" (??0?$KeyCompare@VTester@@@@QAE@XZ) already defined in MapTest.obj MapTest.cpp is the test harness class in which I wrote the test case. I have used include guards as well, to stop multiple inclusions. Any idea what the matter is?? Thank you very much!!

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• C++ find multiple keys from a std::multimap

  - by sch0ck9

  I have a STL::multimap and I search to populate a std::list with value which key is duplicated. Can I find/insert to a std::list the value of elements for all key where count 1 without counting them one by one? std::multimap<int, std::string> mm ; mm[0] = "a" ; mm[1] = "b" ; mm[0] = "c" ; mm[2] = "j" ; mm[2] = "k" ; std::list<std::string> lst ; lst might contains "a" ,"c","j","k" ; I try this template <class K, class V> class extract_value { private: K last_key_ ; std::list<V> m_list_value ; std::pair<K, V> first_elem ; public: extract_value(const K& k_): last_key_(k_) { } void operator() (std::pair<const K, V> elem) { if (last_key_ == elem.first) { m_list_value.push_back(elem.second) ; } else { // First entry last_key_ = elem.first; first_elem= elem ; } } std::list<V> get_value() { return m_list_value ; } }; ex_ = for_each(mm.begin(),mm.end(), extract_value<int, std::string>(0)) ; std::list<std::string> lst = ex_.get_value() ; I'm not sure that this code compile.

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• What is the difference between Inversion of Control and Dependency injection in C++?

  - by rlbond

  I've been reading recently about DI and IoC in C++. I am a little confused (even after reading related questions here on SO) and was hoping for some clarification. It seems to me that being familiar with the STL and Boost leads to use of dependency injection quite a bit. For example, let's say I made a function that found the mean of a range of numbers: template <typename Iter> double mean(Iter first, Iter last) { double sum = 0; size_t number = 0; while (first != last) { sum += *(first++); ++number; } return sum/number; }; Is this dependency injection? Inversion of control? Neither? Let's look at another example. We have a class: class Dice { public: typedef boost::mt19937 Engine; Dice(int num_dice, Engine& rng) : n_(num_dice), eng_(rng) {} int roll() { int sum = 0; for (int i = 0; i < num_dice; ++i) sum += boost::uniform_int<>(1,6)(eng_); return sum; } private: Engine& eng_; int n_; }; This seems like dependency injection. But is it inversion of control? Also, if I'm missing something, can someone help me out?

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• Are there any code critique sites or similar resources?

  - by Ukko

  I have noticed when people post example code illustrating some issue that they are having often they will gather a number of comments addressing the quality of the code they presented and not the actual problem asked. This is very helpful--if not well directed. Often, this is wasted effort since the asker is often not receptive and the code is often chopped down to something small to post leaving lots of rough edges. In the old days you would see people asking questions like this on comp.lang.lisp and other parts of the comp.lang hierarchy. But that bit of the net kind of sank into the sewers of neglect. Is there a comparable one-stop-shop today? I am partially asking for selfish reasons, I know how to write good idiomatic C, Lisp, O'Caml, and Java code. But I learned C++ pre-template and STL, those rusty skills are not really applicable to today's C++. I have picked up languages like Scala in a vacuum and get by, but am I really doing it correctly? There are so many ways you can abuse a language, I am currently working against a codebase of Fortran written in C, and I recognize and loathe the "that guy" who wrote it. I don't want to be someone else's "that guy" if I can help it. Just because it works does not mean that one did not totally miss the boat on how it should have been done. Do you seek out this type of critique? If so how, where and why? What types of benefits do you derive from it? How about abuse and trolls?

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