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• Weird behaviour of C++ destructors

  - by Vilx-

  #include <iostream> #include <vector> using namespace std; int main() { vector< vector<int> > dp(50000, vector<int>(4, -1)); cout << dp.size(); } This tiny program takes a split second to execute when simply run from the command line. But when run in a debugger, it takes over 8 seconds. Pausing the debugger reveals that it is in the middle of destroying all those vectors. WTF? Note - Visual Studio 2008 SP1, Core 2 Duo 6700 CPU with 2GB of RAM. Added: To clarify, no, I'm not confusing Debug and Release builds. These results are on one and the same .exe, without even any recompiling inbetween. In fact, switching between Debug and Release builds changes nothing.

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• Access reading error when using class member variable

  - by bsg

  Hi, I have a class with private member variables declared in a header file. In my constructor, I pass in some filenames and create other objects using those names. This works fine. When I try to add another member variable, however, and initialize it in the constructor, I get an access reading violation. I sent the code to someone else and it works fine on his computer. Any idea what could be wrong? Here is the offending code: The .h file: class QUERYMANAGER { INDEXCACHE *cache; URLTABLE *table; SNIPPET *snip; int* iquery[MAX_QUERY_LENGTH]; int* metapointers[MAX_QUERY_LENGTH]; int blockpointers[MAX_QUERY_LENGTH]; int docpositions[MAX_QUERY_LENGTH]; int numberdocs[MAX_QUERY_LENGTH]; int frequencies[MAX_QUERY_LENGTH]; int docarrays[MAX_QUERY_LENGTH][256]; int qsize; public: QUERYMANAGER(); QUERYMANAGER(char *indexfname, char *btfname, char *urltablefname, char *snippetfname, char *snippetbtfname); ~QUERYMANAGER(); This is the .cpp file: #include "querymanagernew.h" #include "snippet.h" using namespace std; QUERYMANAGER::QUERYMANAGER(char *indexfname, char *btfname, char *urltablefname, char *snippetfname, char *snippetbtfname){ cache = new INDEXCACHE(indexfname, btfname); table = new URLTABLE(urltablefname); snip = new SNIPPET(snippetfname, snippetbtfname); //this is where the error occurs qsize = 0; } I am totally at a loss as to what is causing this - any ideas? Thanks, bsg

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• Idiomatic STL: Iterating over a list and inserting elements

  - by mkilling

  I'm writing an algorithm that iterates over a list of points, calculates the distance between them and inserts additional points if the distance is too great. However I seem to be lacking the proper familiarity with STL to come up with an elegant solution. I'm hoping that I can learn something, so I'll just show you my code. You might have some hints for me. for (std::list<PathPoint>::iterator it = ++points_.begin(); it != points_.end(); it++) { Vector curPos = it->getPosition(); Vector prevPos = (--it)->getPosition(); Vector vecFromPrev = curPos - prevPos; float distance = vecFromPrev.abs(); it++; if (distance > MAX_DISTANCE_BETWEEN_POINTS) { int pointsToInsert = (int)(distance / MAX_DISTANCE_BETWEEN_POINTS); Vector curPos = prevPos; for (int i = 0; i < pointsToInsert; i++) { curPos += vecFromPrev / pointsToInsert; it = points_.insert(it, PathPoint(curPos, false)); it++; } } }

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• How to get a number closest to the average in c++?

  - by Alex Zielinski

  What I'm trying to achieve is to take the average of the numbers stored in the array and find the number which is closest to it. My code compiles, but has an error just after starting. I think it's something to do with the memory handling (I don't feel confident with pointers, etc. yet) Could some nice guy take a look at my code and tell me what's wrong with it? (don't be hard on me, I'm a beginner) #include <iostream> #include <cmath> using namespace std; double* aver(double* arr, size_t size, double& average); int main() { double arr[] = {1,2,3,4,5,7}; size_t size = sizeof(arr)/sizeof(arr[0]); double average = 0; double* p = aver(arr,size,average); cout << *p << " " << average << endl; } double* aver(double* arr, size_t size, double& average){ int i,j,sum; double* m = 0; int tmp[7]; for(i=0;i<size;i++) sum += arr[i]; average = sum/size; for(j=0;j<size;j++){ tmp[j] = arr[j] - average; if(abs(tmp[j])>*m) *m = tmp[j]; } return m; }

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• I am trying to have a wall follow robot but there are errors on the names not being declared in my s

  - by Sam

  #include <iostream> #include <libplayerc++/playerc++.h> using namespace std; int main(int argc, char *argv[]) { using namespace PlayerCc; PlayerClient robot("localhost"); BumperProxy bp(&robot,0); Position2dProxy pp(&robot,0); pp.SetMotorEnable(true); for(;;) double turnrate, speed; double error; bool wall; motor_a_speed(0); motor_c_speed(0); while(1) { front_bumper = SENSOR_2; left_bumper = SENSOR_3; if (front_bumper > 2) { if (left_bumper < 3) { motor_a_speed(5); motor_c_speed(drive_speed); motor_a_dir(fwd); motor_c_dir(fwd); } else { motor_a_speed(drive_speed); motor_c_speed(5); motor_a_dir(rev); motor_c_dir(rev); } } else { motor_a_speed(drive_speed); motor_c_speed(drive_speed); motor_a_dir(brake); motor_c_dir(brake); mrest(100); cputs("bump"); motor_a_dir(fwd); motor_c_dir(rev); msleep(450); cputs("right"); motor_a_speed(10); motor_a_dir(fwd); motor_c_dir(fwd); mrest(1300); } pp.SetSpeed(speed, turnrate); } }

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• how to templatize partial template specializations?

  - by Kyle

  I'm not even sure what title to give this question; hopefully the code will demonstrate what I'm trying to do: #include <string> #include <list> using namespace std; template<typename A> class Alpha { public: A m_alpha_a; }; template<typename B> class Bravo { public: B m_bravo_b; }; template<> class Alpha<string> { public: string m_alpha_string; }; template<typename B> template<> class Alpha<Bravo<B> > { public: Bravo<B> m_bravo_class; // Line A }; int main() { Alpha<int> alpha_int; alpha_int.m_alpha_a= 4; Alpha<string> alpha_string; alpha_string.m_alpha_string = "hi"; Alpha<Bravo<int> > alpha_bravo_int; alpha_bravo_int.m_bravo_class.m_bravo_b = 9; }; I want to write a specialization for Alpha<A> when A is of any type Bravo<B>, but the compiler says invalid explicit specialization before ‘’ token enclosing class templates are not explicitly specialized (Referring to // Line A.) What's the correct syntax to do what I want?

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• determining True/False.

  - by sil3nt

  Hi there, the following code #include <iostream> using namespace std; int main(){ char greeting[50] = "goodmorning everyone"; char *s1 = greeting; char *s2 = &greeting[7]; bool test = s2-s1; cout << "s1 is: " << s1 << endl; cout << "s2 is: " << s2 << endl; if (test == true ){ cout << "test is true and is: " << test << endl; } if (test == false){ cout<< "test is false and is: " << test << endl; } return 0; } outputs: s1 is: goodmorning everyone s2 is: ning everyone test is true and is: 1 here what does the line bool test = s2-s1; actually evaluate?, is it the length of the string?. If so, then seeing as s2 is a smaller than s1 it should be negative correct?, and yet the output is true?. Also if i change it to bool test = s1-s2; I still end up with the same result. So it doesnt matter whether its negative or positive the it will be true? and only false when 0?. what does the s2-s1 mean? -cheers (trying to get rid of doubts:))

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• error C2512 in precompiled header file?

  - by SoloMael

  I'm having a ridiculously strange problem. When I try to run the program below, there's an error message that says: "error C2512: 'Record' : no appropriate default constructor available". And when I double-click it, it directs me to a precompiled read-only header file named "xmemory0". Do they expect me to change a read-only file? Here's the segment of code in the file it directs me to: void construct(_Ty *_Ptr) { // default construct object at _Ptr ::new ((void *)_Ptr) _Ty(); // directs me to this line } Here's the program: #include <iostream> #include <vector> #include <string> using namespace std; const int NG = 4; // number of scores struct Record { string name; // student name int scores[NG]; double average; // Calculate the average // when the scores are known Record(int s[], double a) { double sum = 0; for(int count = 0; count != NG; count++) { scores[count] = s[count]; sum += scores[count]; } average = a; average = sum / NG; } }; int main() { // Names of the class string names[] = {"Amy Adams", "Bob Barr", "Carla Carr", "Dan Dobbs", "Elena Evans"}; // exam scores according to each student int exams[][NG]= { {98, 87, 93, 88}, {78, 86, 82, 91}, {66, 71, 85, 94}, {72, 63, 77, 69}, {91, 83, 76, 60}}; vector<Record> records(5); return 0; }

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• Is there stl and utf8 friendly C++ Wrapper for ICU, or other powerful unicode library

  - by artyom

  Hello, I need a good Unicode library for C++. I need Transformations in Unicode sensitive way. For example sort all strings in case insensitive way and get their first characters for index. Convert to upper and to lower various Unicode strings. Split text in reasonable position -- words that would work for Chinese and Japanese as well. Formatting numbers, dates in locale sensitive way (should be thread safe). Transparent support of utf8 (primary internal representation). As far as I know the best library is ICU. However, I can't find normal developer friendly API documentation with examples. Also as far as I see, it is not too friendly with modern C++ design, work with STL and so on. Like this std::string msg; unistring umsg.from_utf8(msg); unistring::word_iterator wi; for(wi=umsg.words().begin(),n=0;wi!=usmg.words().wi_end(),n<10;++wi,++n) ; msg=umsg.substr(umsg.words().begin(),wi).to_utf8(); cout<<_("Five 10 words are ")<<msg; Does anybody know good STL friendly ICU wrapper released under Open Source license preferred permissive like MIT or Boost, but others LGPLv2 compatible are ok as well. Is there another high quality library similar to ICU? Platform: UNIX/POSIX, Windows support is not required. Thanks, Artyom Edit: Unfortunatly I wasn't logged in so I can't make asnver accepted... I had attached the ansver by myself.

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• sorting names in a linked list

  - by sil3nt

  Hi there, I'm trying to sort names into alphabetical order inside a linked list but am getting a run time error. what have I done wrong here? #include <iostream> #include <string> using namespace std; struct node{ string name; node *next; }; node *A; void addnode(node *&listpointer,string newname){ node *temp; temp = new node; if (listpointer == NULL){ temp->name = newname; temp->next = listpointer; listpointer = temp; }else{ node *add; add = new node; while (true){ if(listpointer->name > newname){ add->name = newname; add->next = listpointer->next; break; } listpointer = listpointer->next; } } } int main(){ A = NULL; string name1 = "bob"; string name2 = "tod"; string name3 = "thomas"; string name4 = "kate"; string name5 = "alex"; string name6 = "jimmy"; addnode(A,name1); addnode(A,name2); addnode(A,name3); addnode(A,name4); addnode(A,name5); addnode(A,name6); while(true){ if(A == NULL){break;} cout<< "name is: " << A->name << endl; A = A->next; } return 0; }

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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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• Enums, Constructor overloads with similar conversions.

  - by David Thornley

  Why does VisualC++ (2008) get confused 'C2666: 2 overloads have similar conversions' when I specify an enum as the second parameter, but not when I define a bool type? Shouldn't type matching already rule out the second constructor because it is of a 'basic_string' type? #include <string> using namespace std; enum EMyEnum { mbOne, mbTwo }; class test { public: #if 1 // 0 = COMPILE_OK, 1 = COMPILE_FAIL test(basic_string<char> myString, EMyEnum myBool2) { } test(bool myBool, bool myBool2) { } #else test(basic_string<char> myString, bool myBool2) { } test(bool myBool, bool myBool2) { } #endif }; void testme() { test("test", mbOne); } I can work around this by specifying a reference 'ie. basic_string &myString' but not if it is 'const basic_string &myString'. Also calling explicitly via "test((basic_string)"test", mbOne);" also works. I suspect this has something to do with every expression/type being resolved to a bool via an inherent '!=0'. Curious for comments all the same :)

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• g++ problem with -l option and PostgreSQL

  - by difek

  Hi I've written simple program. Here a code: #include <iostream> #include <stdio.h> #include <D:\Program Files\PostgreSQL\8.4\include\libpq-fe.h> #include <string> using namespace std; int main() { PGconn *conn; PGresult *res; int rec_count; int row; int col; cout << "ble ble: " << 8 << endl; conn = PQconnectdb("dbname=db_pm host=localhost user=postgres password=postgres"); if (PQstatus(conn) == CONNECTION_BAD) { puts("We were unable to connect to the database"); exit(0); } } I'm trying to connect with PostgreSQL. I compile this code with following command: gcc -I/"d:\Program Files\PostgreSQL\" -L/"d:\Program Files\PostgreSQL\8.4\lib\" -lpq -o firstcpp.o firstcpp.cpp This command is from following site: http://www.mkyong.com/database/how-to-building-postgresql-libpq-programs/ And when I compile it I get following error: /cygnus/cygwin-b20/H-i586-cygwin32/i586-cygwin32/bin/ld: cannot open -lpq: No such file or directory collect2: ld returned 1 exit status Does anyone help me? Difek

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• g++ on MacOSX doesn't work with -arch ppc64

  - by Albert

  I am trying to build a Universal binary on MacOSX with g++. However, it doesn't really work. I have tried with this simple dummy code: #include <iostream> using namespace std; int main() { cout << "Hello" << endl; } This works fine: % g++ test.cpp -arch i386 -arch ppc -arch x86_64 -o test % file test test: Mach-O universal binary with 3 architectures test (for architecture i386): Mach-O executable i386 test (for architecture ppc7400): Mach-O executable ppc test (for architecture x86_64): Mach-O 64-bit executable x86_64 However, this does not: % g++ test.cpp -arch i386 -arch ppc -arch x86_64 -arch ppc64 -o test In file included from test.cpp:1: /usr/include/c++/4.2.1/iostream:44:28: error: bits/c++config.h: No such file or directory In file included from /usr/include/c++/4.2.1/ios:43, from /usr/include/c++/4.2.1/ostream:45, from /usr/include/c++/4.2.1/iostream:45, from test.cpp:1: /usr/include/c++/4.2.1/iosfwd:45:29: error: bits/c++locale.h: No such file or directory /usr/include/c++/4.2.1/iosfwd:46:25: error: bits/c++io.h: No such file or directory In file included from /usr/include/c++/4.2.1/bits/ios_base.h:45, from /usr/include/c++/4.2.1/ios:48, from /usr/include/c++/4.2.1/ostream:45, from /usr/include/c++/4.2.1/iostream:45, from test.cpp:1: /usr/include/c++/4.2.1/ext/atomicity.h:39:23: error: bits/gthr.h: No such file or directory /usr/include/c++/4.2.1/ext/atomicity.h:40:30: error: bits/atomic_word.h: No such file or directory ... Any idea why that is? I have installed Xcode 3.2.2 with all SDKs it comes with.

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• cast operator to base class within a thin wrapper derived class

  - by miked

  I have a derived class that's a very thin wrapper around a base class. Basically, I have a class that has two ways that it can be compared depending on how you interpret it so I created a new class that derives from the base class and only has new constructors (that just delegate to the base class) and a new operator==. What I'd like to do is overload the operator Base&() in the Derived class so in cases where I need to interpret it as the Base. For example: class Base { Base(stuff); Base(const Base& that); bool operator==(Base& rhs); //typical equality test }; class Derived : public Base { Derived(stuff) : Base(stuff) {}; Derived(const Base& that) : Base(that) {}; Derived(const Derived& that) : Base(that) {}; bool operator==(Derived& rhs); //special case equality test operator Base&() { return (Base&)*this; //Is this OK? It seems wrong to me. } }; If you want a simple example of what I'm trying to do, pretend I had a String class and String==String is the typical character by character comparison. But I created a new class CaseInsensitiveString that did a case insensitive compare on CaseInsensitiveString==CaseInsensitiveString but in all other cases just behaved like a String. it doesn't even have any new data members, just an overloaded operator==. (Please, don't tell me to use std::string, this is just an example!) Am I going about this right? Something seems fishy, but I can't put my finger on it.

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• Constructor or Assignment Operator

  - by ju

  Can you help me is there definition in C++ standard that describes which one will be called constructor or assignment operator in this case: #include <iostream> using namespace std; class CTest { public: CTest() : m_nTest(0) { cout << "Default constructor" << endl; } CTest(int a) : m_nTest(a) { cout << "Int constructor" << endl; } CTest(const CTest& obj) { m_nTest = obj.m_nTest; cout << "Copy constructor" << endl; } CTest& operatorint rhs) { m_nTest = rhs; cout << "Assignment" << endl; return *this; } protected: int m_nTest; }; int _tmain(int argc, _TCHAR* argv[]) { CTest b = 5; return 0; } Or is it just a matter of compiler optimization?

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• PDCurses TUI with C++ Win32 console application

  - by Bach

  I have downloaded pdcurses source and was able to successfully include curses.h in my project, linked the pre-compiled library and all good. After few hours of trying out the library, I saw the tuidemo.c in the demos folder, compiled it into an executable and brilliant! exactly what I needed for my project. Now the problem is that it's a C code, and I am working on a C++ project in VS c++ 2008. The files I need are tui.c and tui.h How can I include that C file in my C++ code? I saw few suggestions here but the compiler was not too happy with 100's of warnings and errors. How can I go on including/using that TUI pdcurses includes!? Thanks EDIT: I added extern "C" statement, so my test looks like this now, but I'm getting some other type of error #include <stdio.h> #include <stdlib.h> using namespace std; extern "C" { #include <tui.h> } void sub0(void) { //do nothing } void sub1(void) { //do nothing } int main (int argc, char * const argv[]) { menu MainMenu[] = { { "Asub", sub0, "Go inside first submenu" }, { "Bsub", sub1, "Go inside second submenu" }, { "", (FUNC)0, "" } /* always add this as the last item! */ }; startmenu(MainMenu, "TUI - 'textual user interface' demonstration program"); return 0; } Although it is compiling successfully, it is throwing an Error at runtime: 0xC0000005: Access violation reading location 0x021c52f9 at line startmenu(MainMenu, "TUI - 'textual user interface' demonstration program"); Not sure where to go from here. thanks again.

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• Mixing c++ standard strings and windows API

  - by JB

  Many windows APIs take a pointer to a buffer and a size element but the result needs to go into a c++ string. (I'm using windows unicode here so they are wstrings) Here is an example :- #include <iostream> #include <string> #include <vector> #include <windows.h> using namespace std; // This is the method I'm interested in improving ... wstring getComputerName() { vector<wchar_t> buffer; buffer.resize(MAX_COMPUTERNAME_LENGTH+1); DWORD size = MAX_COMPUTERNAME_LENGTH; GetComputerNameW(&buffer[0], &size); return wstring(&buffer[0], size); } int main() { wcout << getComputerName() << "\n"; } My question really is, is this the best way to write the getComputerName function so that it fits into C++ better, or is there a better way? I don't see any way to use a string directly without going via a vector unless I missed something? It works fine, but somehow seems a little ugly. The question isn't about that particular API, it's just a convenient example.

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• Why do I get CA1806 when I catch exception in C++/CLI?

  - by brickner

  I've recently upgraded my project from Visual Studio 2008 to Visual Studio 2010. By enabling Code Analysis and compiling in Release, I'm getting warning CA1806: Do not ignore method results. I've managed to reduce the code that produces the warning to this code: .h file: public ref class Foo { public: void Bar(); }; .cpp file: void Foo::Bar() { try { } catch (const std::exception&) // here I get the warning { } } the warning: CA1806 : Microsoft.Usage : 'Foo::Bar(void)' calls 'Global::__CxxRegisterExceptionObject(void*, void*)' but does not use the HRESULT or error code that the method returns. This could lead to unexpected behavior in error conditions or low-resource situations. Use the result in a conditional statement, assign the result to a variable, or pass it as an argument to another method. If I try to use the exception value or do catch(...) the warning still appears. If I catch managed exceptions instead or compile in Debug I don't get the warning. Why do I get this warning? UPDATE I've decided to open a bug report on Microsoft Connect.

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• Sharepoint user details not visible to other users

  - by richardoz

  I am managing a SharePoint site that uses Form Based Authentication. We have several generic lists, document libraries and active task lists that users can create update and delete. Users can use the people pickers to select/search for everyone. But the users cannot see other users names, email addresses etc. in display lists or the people pickers. If I log in as the site collection administrator, I can see everyones details. So I know the data is available. Updated details on this problem (non-administrators) SharePoint users cannot see other users information. Example: User A assigns a task to user B. User A creates a new task and uses the people picker to find user B. User B is only visible by the login name “bname” and any information about user B is not visible or searchable within the people picker. Once user B is assigned the task, user A no longer sees the name in the task list – even though user A created it. No modified by, created by, assigned to or owner field data is visible to non-administrator users. Facts: Extranet site is configured to use Forms Based Authentication. Intranet uses windows based authentication Users of both the intranet and extranet have the same problem All databases are local The site uses SSRS integration SharePoint WSS on Windows 2003 Std -- After activating the verbose logging it looks like SharePoint is definately asking SQL server for only the user info for the currently logged in user: SELECT TOP 6 /lots-of-columns/ FROM UserData INNER MERGE JOIN Docs AS t1 ON ( 1 = 1 AND UserData.[tp_RowOrdinal] = 0 AND t1.SiteId = UserData.tp_SiteId AND t1.SiteId = @L2 AND t1.DirName = UserData.tp_DirName AND t1.LeafName = UserData.tp_LeafName AND t1.Level = UserData.tp_Level AND t1.IsCurrentVersion = 1 AND (1 = 1) ) LEFT OUTER JOIN AllUserData AS t2 ON ( UserData.[tp_Author]=t2.[tp_ID] AND UserData.[tp_RowOrdinal] = 0 AND t2.[tp_RowOrdinal] = 0 AND ( (t2.tp_IsCurrent = 1) ) AND t2.[tp_CalculatedVersion] = 0 AND t2.[tp_DeleteTransactionId] = 0x AND t2.tp_ListId = @L3 AND UserData.tp_ListId = @L4 AND t2.[tp_Author]=162 /* this is the currently logged in user */ ) WHERE (UserData.tp_IsCurrent = 1) AND UserData.tp_SiteId=@L2 AND (UserData.tp_DirName=@DN) AND UserData.tp_RowOrdinal=0 AND ( ( (UserData.[datetime1] IS NULL ) OR (UserData.[datetime1] = @L5DTP) ) AND t1.SiteId=@L2 AND (t1.DirName=@DN) ) ORDER BY UserData.[tp_Modified] Desc, UserData.[tp_ID] Asc Again, any ideas would be appreciated.

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• Overloading operator>> to a char buffer in C++ - can I tell the stream length?

  - by exscape

  I'm on a custom C++ crash course. I've known the basics for many years, but I'm currently trying to refresh my memory and learn more. To that end, as my second task (after writing a stack class based on linked lists), I'm writing my own string class. It's gone pretty smoothly until now; I want to overload operator that I can do stuff like cin my_string;. The problem is that I don't know how to read the istream properly (or perhaps the problem is that I don't know streams...). I tried a while (!stream.eof()) loop that .read()s 128 bytes at a time, but as one might expect, it stops only on EOF. I want it to read to a newline, like you get with cin to a std::string. My string class has an alloc(size_t new_size) function that (re)allocates memory, and an append(const char *) function that does that part, but I obviously need to know the amount of memory to allocate before I can write to the buffer. Any advice on how to implement this? I tried getting the istream length with seekg() and tellg(), to no avail (it returns -1), and as I said looping until EOF (doesn't stop reading at a newline) reading one chunk at a time.

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• How to implement generic callbacks in C++

  - by Kylotan

  Forgive my ignorance in asking this basic question but I've become so used to using Python where this sort of thing is trivial that I've completely forgotten how I would attempt this in C++. I want to be able to pass a callback to a function that performs a slow process in the background, and have it called later when the process is complete. This callback could be a free function, a static function, or a member function. I'd also like to be able to inject some arbitrary arguments in there for context. (ie. Implementing a very poor man's coroutine, in a way.) On top of that, this function will always take a std::string, which is the output of the process. I don't mind if the position of this argument in the final callback parameter list is fixed. I get the feeling that the answer will involve boost::bind and boost::function but I can't work out the precise invocations that would be necessary in order to create arbitrary callables (while currying them to just take a single string), store them in the background process, and invoke the callable correctly with the string parameter.

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• template style matrix implementation in c

  - by monkeyking

  From time to time I use the following code for generating a matrix style datastructure typedef double myType; typedef struct matrix_t{ |Compilation started at Mon Apr 5 02:24:15 myType **matrix; | size_t x; |gcc structreaderGeneral.c -std=gnu99 -lz size_t y; | }matrix; |Compilation finished at Mon Apr 5 02:24:15 | | matrix alloc_matrix(size_t x, size_t y){ | if(0) | fprintf(stderr,"\t-> Alloc matrix with dim (%lu,%lu) byteprline=%lu bytetotal:%l\| u\n",x,y,y*sizeof(myType),x*y*sizeof(myType)); | | myType **m = (myType **)malloc(x*sizeof(myType **)); | for(size_t i=0;i<x;i++) | m[i] =(myType *) malloc(y*sizeof(myType *)); | | matrix ret; | ret.x=x; | ret.y=y; | ret.matrix=m; | return ret; | } And then I would change my typedef accordingly if I needed a different kind of type for the entries in my matrix. Now I need 2 matrices with different types, an easy solution would be to copy/paste the code, but is there some way to do a template styled implementation. Thanks

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• Consulting a Prolog Source Code from within a VS2008 Solution File

  - by Joshua Green

  I have a Prolog file (Hanoi.pl) containing the code for solving the Hanoi Towers puzzle: hanoi( N ):- move( N, left, middle, right ). move( 0, _, _, _ ):- !. move( N, A, B, C ):- M is N-1, move( M, A, C, B ), inform( A, B ), move( M, C, B, A ). inform( X, Y ):- write( 'move a disk from ' ), write( X ), write( ' to ' ), writeln( Y ). I also have a C++ file written in VS2008 IDE: #include <iostream> #include <string> #include <stdio.h> #include <stdlib.h> using namespace std; #include "SWI-cpp.h" #include "SWI-Prolog.h" predicate_t phanoi; term_t t0; int main(int argc, char** argv) { long n = 5; int rval; if ( !PL_initialise(1, argv) ) PL_halt(1); PL_put_integer( t0, n ); phanoi = PL_predicate( "hanoi", 1, NULL ); rval = PL_call_predicate( NULL, PL_Q_NORMAL, phanoi, t0 ); system( "PAUSE" ); } How can I consult my Prolog source code (Hanoi.pl) from within my C++ code? Not from the Command Prompt - from the code, something like include or consult or compile? It is located in the same folder as my cpp file. Thanks,

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• How to avoid using the plld.exe utility in VS2008 (for linking C++ and Prolog codes)

  - by Joshua Green

  Here is my code in its entirety: Trying "listing." at the Prolog prompt that pops up when I run the program confirms that my Prolog source code has been loaded (consulted). #include <iostream> #include <fstream> #include <string> #include <math.h> #include <stdio.h> #include <stdlib.h> #include <stdafx.h> using namespace std; #include "Windows.h" #include "ctype.h" #include "SWI-cpp.h" #include "SWI-Prolog.h" #include "SWI-Stream.h" int main(int argc, char** argv) { argc = 4; argv[0] = "libpl.dll"; argv[1] = "-G32m"; argv[2] = "-L32m"; argv[3] = "-T32m"; PL_initialise(argc, argv); if ( !PL_initialise(argc, argv) ) PL_halt(1); PlCall( "consult(swi('plwin.rc'))" ); PlCall( "consult('hello.pl')" ); PL_halt( PL_toplevel() ? 0 : 1 ); } So this is how to load a Prolog source code (hello.pl) at run time into VS2008 without having to use plld at the VS command prompt.

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