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  • In Delphi 7, why can I assign a value to a const?

    - by Blorgbeard
    I copied some Delphi code from one project to another, and found that it doesn't compile in the new project, though it did in the old one. The code looks something like this: procedure TForm1.CalculateGP(..) const Price : money = 0; begin ... Price := 1.0; ... end; So in the new project, Delphi complains that "left side cannot be assigned to" - understandable! But this code compiles in the old project. So my question is, why? Is there a compiler switch to allow consts to be reassigned? How does that even work? I thought consts were replaced by their values at compile time?

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  • Why does C's "fopen" take a "const char *" as its second argument?

    - by Chris Cooper
    It has always struck me as strange that the C function "fopen" takes a "const char *" as the second argument. I would think it would be easier to both read your code and implement the library's code if there were bit masks defined in stdio.h, like "IO_READ" and such, so you could do things like: FILE* myFile = fopen("file.txt", IO_READ & IO_WRITE); Is there a programmatic reason for the way it actually is, or is it just historic? (i.e. "That's just the way it is.")

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  • Why pass by const reference instead of by value?

    - by Maulrus
    From what I understand: when you pass by value, the function makes a local copy of the passed argument and uses that; when the function ends, it goes out of scope. When you pass by const reference, the function uses a reference to the passed argument that can't be modified. I don't understand, however, why one would choose one over the other, except in a situation where an argument needs to be modified and returned. If you had a void function where nothing is getting returned, why choose one over the other?

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  • Is there a way to receive data as unsigned char over UDP on Qt?

    - by user269037
    I need to send floating point numbers using a UDP connection to a Qt application. Now in Qt the only function available is qint64 readDatagram ( char * data, qint64 maxSize, QHostAddress * address = 0, quint16 * port = 0 ) which accepts data in the form of signed character buffer. I can convert my float into a string and send it but it will obviously not be very efficient converting a 4 byte float into a much longer sized character buffer. I got hold of these 2 functions to convert a 4 byte float into an unsinged 32 bit integer to transfer over network which works fine for a simple C++ UDP program but for Qt I need to receive the data as unsigned char. Is it possible to avoid converting the floatinf point data into a string and then sending it? uint32_t htonf(float f) { uint32_t p; uint32_t sign; if (f < 0) { sign = 1; f = -f; } else { sign = 0; } p = ((((uint32_t)f)&0x7fff)<<16) | (sign<<31); // Whole part and sign. p |= (uint32_t)(((f - (int)f) * 65536.0f))&0xffff; // Fraction. return p; } float ntohf(uint32_t p) { float f = ((p>>16)&0x7fff); // Whole part. f += (p&0xffff) / 65536.0f; // Fraction. if (((p>>31)&0x1) == 0x1) { f = -f; } // Sign bit set. return f; }

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  • How do you specify a 64 bit unsigned int const 0x8000000000000000 in VS2008?

    - by Mark Franjione
    I read about the Microsoft specific suffix "i64" for integer constants. I want to do an UNsigned shift to a ULONGLONG. ULONGLONG bigNum64 = 0x800000000000000i64 >> myval; In normal C, I would use the suffix "U", e.g. the similar 32 bit operation would be ULONG bigNum32 = 0x80000000U >> myval; I do NOT want the 2's complement sign extension to propogate through the high bits. I want an UNSIGNED shift on a 64 bit const number. I think my first statement is going to do a SIGNED shift right. I tried 0x800000000000000i64U and 0x800000000000000u64 but got compiler errors.

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  • Noob Objective-C/C++ - Linker Problem/Method Signature Problem

    - by Josh
    There is a static class Pipe, defined in C++ header that I'm including. The static method I'm interested in calling (from Objetive-c) is here: static ERC SendUserGet(const UserId &_idUser,const GUID &_idStyle,const ZoneId &_idZone,const char *_pszMsg); I have access to an objetive-c data structure that appears to store a copy of userID, and zoneID -- it looks like: @interface DataBlock : NSObject { GUID userID; GUID zoneID; } Looked up the GUID def, and its a struct with a bunch of overloaded operators for equality. UserId and ZoneId from the first function signature are #typedef GUID Now when I try to call the method, no matter how I cast it (const UserId), (UserId), etc, I get the following linker error: Ld build/Debug/Seeker.app/Contents/MacOS/Seeker normal i386 cd /Users/josh/Development/project/Mac/Seeker setenv MACOSX_DEPLOYMENT_TARGET 10.5 /Developer/usr/bin/g++-4.2 -arch i386 -isysroot /Developer/SDKs/MacOSX10.5.sdk -L/Users/josh/Development/TS/Mac/Seeker/build/Debug -L/Users/josh/Development/TS/Mac/Seeker/../../../debug -L/Developer/Platforms/iPhoneOS.platform/Developer/usr/lib/gcc/i686-apple-darwin10/4.2.1 -F/Users/josh/Development/TS/Mac/Seeker/build/Debug -filelist /Users/josh/Development/TS/Mac/Seeker/build/Seeker.build/Debug/Seeker.build/Objects-normal/i386/Seeker.LinkFileList -mmacosx-version-min=10.5 -framework Cocoa -framework WebKit -lSAPI -lSPL -o /Users/josh/Development/TS/Mac/Seeker/build/Debug/Seeker.app/Contents/MacOS/Seeker Undefined symbols: "SocPipe::SendUserGet(_GUID const&, _GUID const&, _GUID const&, char const*)", referenced from: -[PeoplePaneController clickGet:] in PeoplePaneController.o ld: symbol(s) not found collect2: ld returned 1 exit status Is this a type/function signature error, or truly some sort of linker error? I have the headers where all these types and static classes are defined #imported -- I tried #include too, just in case, since I'm already stumbling :P Forgive me, I come from a web tech background, so this c-style memory management and immutability stuff is super hazy. Edit: Added full linker error text. Changed "function" to "method" Thanks, Josh

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  • Noob Objective-C/C++ - Linker Problem/Function Def Problem

    - by Josh
    There is a static class Pipe, defined in C++ header that I'm including. The function I'm interested in calling (from Objetive-c) is here: static ERC SendUserGet(const UserId &_idUser,const GUID &_idStyle,const ZoneId &_idZone,const char *_pszMsg); I have access to an objetive-c data structure that appears to store a copy of userID, and zoneID -- it looks like: @interface DataBlock : NSObject { GUID userID; GUID zoneID; } Looked up the GUID def, and its a struct with a bunch of overloaded operators for equality. UserId and ZoneId from the first function signature are #typedef GUID Now when I try to call the function, no matter how I cast it (const UserId), (UserId), etc, I get the following linker error: "Pipe::SendUserGet(_GUID const&, _GUID const&, _GUID const&, char const*)", referenced from: -[PeoplePaneController clickGet:] in PeoplePaneController.o Is this a type/function signature error, or truly some sort of linker error? I have the headers where all these types and static classes are defined #imported -- I tried #include too, just in case, since I'm already stumbling :P Forgive me, I come from a web tech background, so this c-style memory management and immutability stuff is super hazy. Thanks, Josh

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  • Linking errors when building against Boost Unit Test Framework

    - by Rafid
    I am trying to use Boost Unit Test Framework by building a stand alone library as detailed here: http://www.boost.org/doc/libs/1_35_0/libs/test/doc/components/utf/compilation.html So I created a VC library project containing the mentioned files and build it and it was successful. Then I created a test project and referenced the library project I just created, but when I tried to build it, I got the following linking errors: 1>Type.obj : error LNK2019: unresolved external symbol "bool __cdecl boost::test_tools::tt_detail::check_impl(class boost::test_tools::predicate_result const &,class boost::unit_test::lazy_ostream const &,class boost::unit_test::basic_cstring<char const >,unsigned __int64,enum boost::test_tools::tt_detail::tool_level,enum boost::test_tools::tt_detail::check_type,unsigned __int64,...)" (?check_impl@tt_detail@test_tools@boost@@YA_NAEBVpredicate_result@23@AEBVlazy_ostream@unit_test@3@V?$basic_cstring@$$CBD@63@_KW4tool_level@123@W4check_type@123@3ZZ) referenced in function "public: void __cdecl test1::test_method(void)" (?test_method@test1@@QEAAXXZ) 1>BoostUnitTestFramework.lib(framework.obj) : error LNK2019: unresolved external symbol "void __cdecl boost::debug::break_memory_alloc(long)" (?break_memory_alloc@debug@boost@@YAXJ@Z) referenced in function "void __cdecl boost::unit_test::framework::init(class boost::unit_test::test_suite * (__cdecl*)(int,char * * const),int,char * * const)" (?init@framework@unit_test@boost@@YAXP6APEAVtest_suite@23@HQEAPEAD@ZH0@Z) 1>BoostUnitTestFramework.lib(framework.obj) : error LNK2019: unresolved external symbol "void __cdecl boost::debug::detect_memory_leaks(bool)" (?detect_memory_leaks@debug@boost@@YAX_N@Z) referenced in function "void __cdecl boost::unit_test::framework::init(class boost::unit_test::test_suite * (__cdecl*)(int,char * * const),int,char * * const)" (?init@framework@unit_test@boost@@YAXP6APEAVtest_suite@23@HQEAPEAD@ZH0@Z) 1>BoostUnitTestFramework.lib(execution_monitor.obj) : error LNK2019: unresolved external symbol "bool __cdecl boost::debug::attach_debugger(bool)" (?attach_debugger@debug@boost@@YA_N_N@Z) referenced in function "public: int __cdecl boost::detail::system_signal_exception::operator()(unsigned int,struct _EXCEPTION_POINTERS *)" (??Rsystem_signal_exception@detail@boost@@QEAAHIPEAU_EXCEPTION_POINTERS@@@Z) 1>BoostUnitTestFramework.lib(execution_monitor.obj) : error LNK2019: unresolved external symbol "bool __cdecl boost::debug::under_debugger(void)" (?under_debugger@debug@boost@@YA_NXZ) referenced in function "public: int __cdecl boost::execution_monitor::execute(class boost::unit_test::callback0<int> const &)" (?execute@execution_monitor@boost@@QEAAHAEBV?$callback0@H@unit_test@2@@Z) 1>BoostUnitTestFramework.lib(unit_test_main.obj) : error LNK2019: unresolved external symbol "class boost::unit_test::test_suite * __cdecl init_unit_test_suite(int,char * * const)" (?init_unit_test_suite@@YAPEAVtest_suite@unit_test@boost@@HQEAPEAD@Z) referenced in function main 1>C:\Users\Rafid\Workspace\MyPhysics\Builds\VC10\Tests\Debug\Tests.exe : fatal error LNK1120: 6 unresolved externals They seem to be mainly caused by Boost debug library, but I can't see a reason why I should get linking errors putting in mind that Boost debug library only need to be included as header files, rather than linking against as a library! Any ideas?!

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  • Oracle sqlldr: column not allowed here

    - by Wade Williams
    Can anyone spot the error in this attempted data load? The '\\N' is because this is an import of an OUTFILE dump from mysql, which puts \N for NULL fields. The decode is to catch cases where the field might be an empty string, or might have \N. Using Oracle 10g on Linux. load data infile objects.txt discardfile objects.dsc truncate into table objects fields terminated by x'1F' optionally enclosed by '"' (ID INTEGER EXTERNAL NULLIF (ID='\\N'), TITLE CHAR(128) NULLIF (TITLE='\\N'), PRIORITY CHAR(16) "decode(:PRIORITY, BLANKS, NULL, '\\N', NULL)", STATUS CHAR(64) "decode(:STATUS, BLANKS, NULL, '\\N', NULL)", ORIG_DATE DATE "YYYY-MM-DD HH:MM:SS" NULLIF (ORIG_DATE='\\N'), LASTMOD DATE "YYYY-MM-DD HH:MM:SS" NULLIF (LASTMOD='\\N'), SUBMITTER CHAR(128) NULLIF (SUBMITTER='\\N'), DEVELOPER CHAR(128) NULLIF (DEVELOPER='\\N'), ARCHIVE CHAR(4000) NULLIF (ARCHIVE='\\N'), SEVERITY CHAR(64) "decode(:SEVERITY, BLANKS, NULL, '\\N', NULL)", VALUED CHAR(4000) NULLIF (VALUED='\\N'), SRD DATE "YYYY-MM-DD" NULLIF (SRD='\\N'), TAG CHAR(64) NULLIF (TAG='\\N') ) Sample Data (record 1). The ^_ represents the unprintable 0x1F delimiter. 1987^_Component 1987^_\N^_Done^_2002-10-16 01:51:44^_2002-10-16 01:51:44^_import^_badger^_N^_^_N^_0000-00-00^_none Error: Record 1: Rejected - Error on table objects, column SEVERITY. ORA-00984: column not allowed here

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  • Storing class constants (for use as bitmask) in a database?

    - by fireeyedboy
    Let's say I have a class called Medium which can represent different types of media. For instance: uploaded video embedded video uploaded image embedded image I represent these types with contants, like this: class MediumAbstract { const UPLOAD = 0x0001; const EMBED = 0x0010; const VIDEO = 0x0100; const IMAGE = 0x1000; const VIDEO_UPLOAD = 0x0101; // for convenience const VIDEO_EMBED = 0x0110; // for convenience const IMAGE_UPLOAD = 0x1001; // for convenience const IMAGE_EMBED = 0x1010; // for convenience const ALL = 0x1111; // for convenience } Thus, it is easy for me to do a combined search on them on an (abstract) repository, with something like: { public function findAllByType( $type ) { ... } } $media = $repo->findAllByType( MediumAbstract::VIDEO | MediumAbstract::IMAGE_UPLOAD ); // or $media = $repo->findAllByType( MediumAbstract::ALL ); // etc.. How do you feel about using these constant values in a concrete repository like a database? Is it ok? Or should I substitute them with meaningful data in the database. Table medium: | id | type | location | etc.. ------------------------------------------------- | 1 | use constants here? | /some/path | etc.. (Of course I'll only be using the meaningful constants: VIDEO_UPLOAD, VIDEO_EMBED, IMAGE_UPLOAD and IMAGE_EMBED)

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  • Sending 2 dim array using scatter

    - by MPI_Beginner
    I am a beginner in MPI, and i am using C Language, and Simulator for Processors (MPICH2), i wrote the following code to send a 2D array to make 2 processors take a line from it but it produces error when running MPICH2, the code is: int main ( int argc , char *argv[] ) { int rank; int commsize; MPI_Init(&argc, &argv); MPI_Comm_size(MPI_COMM_WORLD,&commsize); MPI_Comm_rank(MPI_COMM_WORLD,&rank); char** name=malloc(2*sizeof(char*)); int i; for(i=0;i<2;i++){ name[i]=malloc(15*sizeof(char)); } name[0]="name"; name[1]="age"; if(rank==0){ char** mArray=malloc(2*sizeof(char*)); MPI_Scatter(&name,1,MPI_CHAR,&mArray,1,MPI_CHAR,0,MPI_COMM_WORLD);//send } else{ char** mArray=malloc(2*sizeof(char*)); int k; for(k=0;k<2;k++){ mArray[k]=malloc(15*sizeof(char)); } MPI_Scatter(&mArray,1,MPI_CHAR,&mArray,1,MPI_CHAR,0,MPI_COMM_WORLD);//receive printf("line is %s \n",mArray[rank-1]); } MPI_Finalize(); }

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  • Coredump in Multithreading Application in RHEL-5

    - by Chinnu
    I am working on multi-threading application it is dumping frequently.I could not able to analyaze the core.The core is showing like this Core was generated by 'thread-process'. Program terminated with signal 6, Aborted. #0 0x00000038f4e30045 in raise () from /lib64/libc.so.6 (gdb) where #0 0x00000038f4e30045 in raise () from /lib64/libc.so.6 #1 0x00000038f4e31ae0 in abort () from /lib64/libc.so.6 #2 0x00000038f4e681bb in __libc_message () from /lib64/libc.so.6 #3 0x00000038f4e72b96 in free () from /lib64/libc.so.6 #4 0x000000000046a137 in std::string::substr () #5 0x000000000042c549 in std::operator<< <char, std::char_traits<char>, std::allocator<char> > () #6 0x000000000042cc1d in std::operator<< <char, std::char_traits<char>, std::allocator<char> > () #7 0x000000000046b069 in std::string::substr () #8 0x000000000046c866 in std::string::substr () #9 0x0000000000431062 in std::operator<< <char, std::char_traits<char>, std::allocator<char> > () #10 0x00000038f5a062e7 in start_thread () from /lib64/libpthread.so.0 #11 0x00000038f4ece3bd in clone () from /lib64/libc.so.6

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  • Facebook Application Parse Error CSS

    - by madphp
    Hi, Im getting some parse erros when loading in my facebook app through the canvas. Its in an iframe. Can anyone tell me where I can start to look for documentation regarding this? Errors whilst loading page from application Parse errors: CSS Error (line 40 char 36): Error in parsing value for property.: 'font' Declaration dropped. CSS Error (line 183 char 18): Expected declaration. Skipped to next declaration. CSS Error (line 272 char 65): Unknown property.: '-webkit-border-radius' Declaration dropped. CSS Error (line 272 char 110): Unknown property.: 'border-radius' Declaration dropped. CSS Error (line 272 char 135): Unknown property.: '-webkit-box-shadow' Declaration dropped. CSS Error (line 272 char 181): Unknown property.: '-moz-box-shadow' Declaration dropped. CSS Error (line 272 char 221): Unknown property.: 'box-shadow' Declaration dropped. CSS Error (line 317 char 23): Unknown property.: '-webkit-border-radius' Declaration dropped. CSS Error (line 319 char 15): Unknown property.: 'border-radius' Declaration dropped. Thanks --Mark

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  • UTF-8 to Unicode conversion

    - by sandeep
    Hi, I am having problems with converting UTF-8 to Unicode. Below is the code: int charset_convert( char * string, char * to_string,char* charset_from, char* charset_to) { char *from_buf, *to_buf, *pointer; size_t inbytesleft, outbytesleft, ret; size_t TotalLen; iconv_t cd; if (!charset_from || !charset_to || !string) /* sanity check */ return -1; if (strlen(string) < 1) return 0; /* we are done, nothing to convert */ cd = iconv_open(charset_to, charset_from); /* Did I succeed in getting a conversion descriptor ? */ if (cd == (iconv_t)(-1)) { /* I guess not */ printf("Failed to convert string from %s to %s ", charset_from, charset_to); return -1; } from_buf = string; inbytesleft = strlen(string); /* allocate max sized buffer, assuming target encoding may be 4 byte unicode */ outbytesleft = inbytesleft *4 ; pointer = to_buf = (char *)malloc(outbytesleft); memset(to_buf,0,outbytesleft); memset(pointer,0,outbytesleft); ret = iconv(cd, &from_buf, &inbytesleft, &pointer, &outbytesleft);ing memcpy(to_string,to_buf,(pointer-to_buf); } main(): int main() { char UTF []= {'A', 'B'}; char Unicode[1024]= {0}; char* ptr; int x=0; iconv_t cd; charset_convert(UTF,Unicode,"UTF-8","UNICODE"); ptr = Unicode; while(*ptr != '\0') { printf("Unicode %x \n",*ptr); ptr++; } return 0; } It should give A and B but i am getting: ffffffff fffffffe 41 Thanks, Sandeep

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  • using a JOIN in an UPDATE in SQL

    - by SDLFunTimes
    Hi, I'm having trouble formulating a legal statement to double the statuses of the suppliers (s) who have shipped (sp) more than 500 units. I've been trying: update s set s.status = s.status * 2 from s join sp on (sp.sno = s.sno) group by sno having sum(qty) > 500; however I'm getting this error from Mysql: ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'from s join sp on (sp.sno = s.sno) group by sno having sum(qty) > 500' at line 1 Does anyone have any ideas about what is wrong with this query? Here's my schema: create table s ( sno char(5) not null, sname char(20) not null, status smallint, city char(15), primary key (sno) ); create table p ( pno char(6) not null, pname char(20) not null, color char(6), weight smallint, city char(15), primary key (pno) ); create table sp ( sno char(5) not null, pno char(6) not null, qty integer not null, primary key (sno, pno) );

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  • Defining < for STL sort algorithm - operator overload, functor or standalone function?

    - by Andy
    I have a stl::list containing Widget class objects. They need to be sorted according to two members in the Widget class. For the sorting to work, I need to define a less-than comparator comparing two Widget objects. There seems to be a myriad of ways to do it. From what I can gather, one can either: a. Define a comparison operator overload in the class: bool Widget::operator< (const Widget &rhs) const b. Define a standalone function taking two Widgets: bool operator<(const Widget& lhs, const Widget& rhs); And then make the Widget class a friend of it: class Widget { // Various class definitions ... friend bool operator<(const Widget& lhs, const Widget& rhs); }; c. Define a functor and then include it as a parameter when calling the sort function: class Widget_Less : public binary_function<Widget, Widget, bool> { bool operator()(const Widget &lhs, const Widget& rhs) const; }; Does anybody know which method is better? In particular I am interested to know if I should do 1 or 2. I searched the book Effective STL by Scott Meyer but unfortunately it does not have anything to say about this. Thank you for your reply.

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  • Which cast am I using?

    - by Knowing me knowing you
    I'm trying to cast away const from an object but it doesn't work. But if I use old C-way of casting code compiles. So which casting I'm suppose to use to achieve this same effect? I wouldn't like to cast the old way. //file IntSet.h #include "stdafx.h" #pragma once /*Class representing set of integers*/ template<class T> class IntSet { private: T** myData_; std::size_t mySize_; std::size_t myIndex_; public: #pragma region ctor/dtor explicit IntSet(); virtual ~IntSet(); #pragma endregion #pragma region publicInterface IntSet makeUnion(const IntSet&)const; IntSet makeIntersection(const IntSet&)const; IntSet makeSymmetricDifference(const IntSet&)const; void insert(const T&); #pragma endregion }; //file IntSet_impl.h #include "StdAfx.h" #include "IntSet.h" #pragma region ctor/dtor template<class T> IntSet<T>::IntSet():myData_(nullptr), mySize_(0), myIndex_(0) { } IntSet<T>::~IntSet() { } #pragma endregion #pragma region publicInterface template<class T> void IntSet<T>::insert(const T& obj) { /*Check if we are initialized*/ if (mySize_ == 0) { mySize_ = 1; myData_ = new T*[mySize_]; } /*Check if we have place to insert obj in.*/ if (myIndex_ < mySize_) {//IS IT SAFE TO INCREMENT myIndex while assigning? myData_[myIndex_++] = &T(obj);//IF I DO IT THE OLD WAY IT WORKS return; } /*We didn't have enough place...*/ T** tmp = new T*[mySize_];//for copying old to temporary basket std::copy(&myData_[0],&myData_[mySize_],&tmp[0]); } #pragma endregion Thanks.

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  • Simple matrix example using C++ template class

    - by skyeagle
    I am trying to write a trivial Matrix class, using C++ templates in an attempt to brush up my C++, and also to explain something to a fellow coder. This is what I have som far: template class<T> class Matrix { public: Matrix(const unsigned int rows, const unsigned int cols); Matrix(const Matrix& m); Matrix& operator=(const Matrix& m); ~Matrix(); unsigned int getNumRows() const; unsigned int getNumCols() const; template <class T> T getCellValue(unsigned int row, unsigned col) const; template <class T> void setCellValue(unsigned int row, unsigned col, T value) const; private: // Note: intentionally NOT using smart pointers here ... T * m_values; }; template<class T> inline T Matrix::getCellValue(unsigned int row, unsigned col) const { } template<class T> inline void Matrix::setCellValue(unsigned int row, unsigned col, T value) { } I'm stuck on the ctor, since I need to allocate a new[] T, it seems like it needs to be a template method - however, I'm not sure I have come accross a templated ctor before. How can I implemnt the ctor?

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  • A public struct inside a class

    - by Koning Baard
    I am new to C++, and let's say I have two classes: Creature and Human: /* creature.h */ class Creature { private: public: struct emotion { /* All emotions are percentages */ char joy; char trust; char fear; char surprise; char sadness; char disgust; char anger; char anticipation; char love; }; }; /* human.h */ class Human : Creature { }; And I have this in my main function in main.cpp: Human foo; My question is: how can I set foo's emotions? I tried this: foo->emotion.fear = 5; But GCC gives me this compile error: error: base operand of '-' has non-pointer type 'Human' This: foo.emotion.fear = 5; Gives: error: 'struct Creature::emotion' is inaccessible error: within this context error: invalid use of 'struct Creature::emotion' Can anyone help me? Thanks P.S. No I did not forget the #includes

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  • C++ Operator Ambiguity

    - by Scott
    Forgive me, for I am fairly new to C++, but I am having some trouble regarding operator ambiguity. I think it is compiler-specific, for the code compiled on my desktop. However, it fails to compile on my laptop. I think I know what's going wrong, but I don't see an elegant way around it. Please let me know if I am making an obvious mistake. Anyhow, here's what I'm trying to do: I have made my own vector class called Vector4 which looks something like this: class Vector4 { private: GLfloat vector[4]; ... } Then I have these operators, which are causing the problem: operator GLfloat* () { return vector; } operator const GLfloat* () const { return vector; } GLfloat& operator [] (const size_t i) { return vector[i]; } const GLfloat& operator [] (const size_t i) const { return vector[i]; } I have the conversion operator so that I can pass an instance of my Vector4 class to glVertex3fv, and I have subscripting for obvious reasons. However, calls that involve subscripting the Vector4 become ambiguous to the compiler: enum {x, y, z, w} Vector4 v(1.0, 2.0, 3.0, 4.0); glTranslatef(v[x], v[y], v[z]); Here are the candidates: candidate 1: const GLfloat& Vector4:: operator[](size_t) const candidate 2: operator[](const GLfloat*, int) <built-in> Why would it try to convert my Vector4 to a GLfloat* first when the subscript operator is already defined on Vector4? Is there a simple way around this that doesn't involve typecasting? Am I just making a silly mistake? Thanks for any help in advance.

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  • Failed to specialize function template

    - by citizencane
    This is homework, although it's already submitted with a different approach. I'm getting the following from Visual Studio 2008 error C2893: Failed to specialize function template 'void std::sort(_RanIt,_RanIt,_Pr)' The code is as follows main.cpp Database<> db; db.loadDatabase(); db.sortDatabase(sort_by_title()); Database.cpp void Database<C>::sortDatabase(const sort_by &s) { std::sort(db_.begin(), db_.end(), s); } And the function objects are defined as struct sort_by : public std::binary_function<const Media *, const Media *, bool> { virtual bool operator()(const Media *l, const Media *r) const = 0; }; struct sort_by_title : public sort_by { bool operator()(const Media *l, const Media *r) const { ... } }; ... What's the cure here? [Edit] Sorry, maybe I should have made the inheritance clear template <typename C = std::vector<Media *> > class Database : public IDatabase<C> [/Edit]

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  • How do I access abstract private data from derived class without friend or 'getter' functions in C++?

    - by John
    So, I am caught up in a dilemma right now. How am I suppose to access a pure abstract base class private member variable from a derived class? I have heard from a friend that it is possible to access it through the base constructor, but he didn't explain. How is it possible? There are some inherited classes from base class. Is there any way to gain access to the private variables ? class Base_button { private: bool is_vis; Rect rButton; public: // Constructors Base_button(); Base_button( const Point &corner, double height, double width ); // Destructor virtual ~ Base_button(); // Accessors virtual void draw() const = 0; bool clicked( const Point &click ) const; bool is_visible() const; // Mutators virtual void show(); virtual void hide(); void move( const Point &loc ); }; class Button : public Base_button { private: Message mButton; public: // Constructors Button(); Button( const Point &corner, const string &label ); // Acessors virtual void draw() const; // Mutators virtual void show(); virtual void hide(); }; I want to be able access Rect and bool in the base class from the subclass

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  • Create a console from within a non-console .NET application.

    - by pauldoo
    How can I open a console window from within a non-console .NET application (so I have a place for System.Console.Out and friends when debugging)? In C++ this can be done using various Win32 APIs: /* EnsureConsoleExists() will create a console window and attach stdout (and friends) to it. Can be useful when debugging. */ FILE* const CreateConsoleStream(const DWORD stdHandle, const char* const mode) { const HANDLE outputHandle = ::GetStdHandle(stdHandle); assert(outputHandle != 0); const int outputFileDescriptor = _open_osfhandle(reinterpret_cast<intptr_t>(outputHandle), _O_TEXT); assert(outputFileDescriptor != -1); FILE* const outputStream = _fdopen(outputFileDescriptor, mode); assert(outputStream != 0); return outputStream; } void EnsureConsoleExists() { const bool haveCreatedConsole = (::AllocConsole() != 0); if (haveCreatedConsole) { /* If we didn't manage to create the console then chances are that stdout is already going to a console window. */ *stderr = *CreateConsoleStream(STD_ERROR_HANDLE, "w"); *stdout = *CreateConsoleStream(STD_OUTPUT_HANDLE, "w"); *stdin = *CreateConsoleStream(STD_INPUT_HANDLE, "r"); std::ios::sync_with_stdio(false); const HANDLE consoleHandle = ::GetStdHandle(STD_OUTPUT_HANDLE); assert(consoleHandle != NULL && consoleHandle != INVALID_HANDLE_VALUE); CONSOLE_SCREEN_BUFFER_INFO info; BOOL result = ::GetConsoleScreenBufferInfo(consoleHandle, &info); assert(result != 0); COORD size; size.X = info.dwSize.X; size.Y = 30000; result = ::SetConsoleScreenBufferSize(consoleHandle, size); assert(result != 0); } }

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  • Item 2, Scott Myers Effective C++ question

    - by user619818
    In Item2 on page 16, (Prefer consts, enums, and inlines to #defines), Scott says: 'Also, though good compilers won't set aside storage for const objects of integer types'. I don't understand this. If I define a const object, eg const int myval = 5; then surely the compiler must set aside some memory (of int size) to store the value 5? Or is const data stored in some special way? This is more a question of computer storage I suppose. Basically, how does the computer store const objects so that no storage is set aside?

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  • Compatibility of Enum Vs. string constants

    - by Yosi
    I was recently told that using Enum: public enum TaskEndState { Error, Completed, Running } may have compatibility/serialization issues, and thus sometimes it's better to use const string: public const string TASK_END_STATE = "END_STATE"; public const string TASK_END_STATE_ERROR = "TASK_END_STATE_ERROR"; public const string TASK_END_STATE_COMPLETE = "TASK_END_STATE_COMPLETE"; public const string TASK_END_STATE_RUNNING = "TASK_END_STATE_RUNNING"; Can you find practical use case where it may happen, is there any guidelines where Enum's should be avoided? Edit: My production environment has multiple WFC services (different versions of the same product). A later version may/or may not include some new properties as Task end state (this is just an example). If we try to deserialize a new Enum value in an older version of a specific service, it may not work.

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