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• How to avoid the following purify detected memory leak in C++?

  - by Abhijeet

  Hi, I am getting the following memory leak.Its being probably caused by std::string. how can i avoid it? PLK: 23 bytes potentially leaked at 0xeb68278 * Suppressed in /vobs/ubtssw_brrm/test/testcases/.purify [line 3] * This memory was allocated from: malloc [/vobs/ubtssw_brrm/test/test_build/linux-x86/rtlib.o] operator new(unsigned) [/vobs/MontaVista/Linux/montavista/pro/devkit/x86/586/target/usr/lib/libstdc++.so.6] operator new(unsigned) [/vobs/ubtssw_brrm/test/test_build/linux-x86/rtlib.o] std::string<char, std::char_traits<char>, std::allocator<char>>::_Rep::_S_create(unsigned, unsigned, std::allocator<char> const&) [/vobs/MontaVista/Linux/montavista/pro/devkit/ x86/586/target/usr/lib/libstdc++.so.6] std::string<char, std::char_traits<char>, std::allocator<char>>::_Rep::_M_clone(std::allocator<char> const&, unsigned) [/vobs/MontaVista/Linux/montavista/pro/devkit/x86/586/tar get/usr/lib/libstdc++.so.6] std::string<char, std::char_traits<char>, std::allocator<char>>::string<char, std::char_traits<char>, std::allocator<char>>(std::string<char, std::char_traits<char>, std::alloc ator<char>> const&) [/vobs/MontaVista/Linux/montavista/pro/devkit/x86/586/target/usr/lib/libstdc++.so.6] uec_UEDir::getEntryToUpdateAfterInsertion(rcapi_ImsiGsmMap const&, rcapi_ImsiGsmMap&, std::_Rb_tree_iterator<std::pair<std::string<char, std::char_traits<char>, std::allocator< char>> const, UEDirData >>&) [/vobs/ubtssw_brrm/uectrl/linux-x86/../src/uec_UEDir.cc:2278] uec_UEDir::addUpdate(rcapi_ImsiGsmMap const&, LocalUEDirInfo&, rcapi_ImsiGsmMap&, int, unsigned char) [/vobs/ubtssw_brrm/uectrl/linux-x86/../src/uec_UEDir.cc:282] ucx_UEDirHandler::addUpdateUEDir(rcapi_ImsiGsmMap, UEDirUpdateType, acap_PresenceEvent) [/vobs/ubtssw_brrm/ucx/linux-x86/../src/ucx_UEDirHandler.cc:374]

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• User defined literal arguments are not constexpr?

  - by Pubby

  I'm testing out user defined literals. I want to make _fac return the factorial of the number. Having it call a constexpr function works, however it doesn't let me do it with templates as the compiler complains that the arguments are not and cannot be constexpr. I'm confused by this - aren't literals constant expressions? The 5 in 5_fac is always a literal that can be evaluated during compile time, so why can't I use it as such? First method: constexpr int factorial_function(int x) { return (x > 0) ? x * factorial_function(x - 1) : 1; } constexpr int operator "" _fac(unsigned long long x) { return factorial_function(x); // this works } Second method: template <int N> struct factorial { static const unsigned int value = N * factorial<N - 1>::value; }; template <> struct factorial<0> { static const unsigned int value = 1; }; constexpr int operator "" _fac(unsigned long long x) { return factorial_template<x>::value; // doesn't work - x is not a constexpr }

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• Google Adwords API response parse

  - by Yun Ling

  I am trying to figure out how to parse the Adword API query response without exceptions and one issue that i came across is that sometimes, the data itself contains comma besides the comma between each column. Say i do a query on Adroup, campaign and impression by using <reportDefinition xmlns="https://adwords.google.com/api/adwords/cm/v201209"> <selector> <fields>CampaignName</fields> <fields>AdgroupName</fields> <fields>Impressions</fields> <predicates> <field>Status</field> <operator>IN</operator> <values>ENABLED</values> <values>PAUSED</values> </predicates> </selector> <reportName>Custom Adgroup Performance Report</reportName> <reportType>ADGROUP_PERFORMANCE_REPORT</reportType> <dateRangeType>LAST_7_DAYS</dateRangeType> <downloadFormat>CSV</downloadFormat> </reportDefinition> Since my campaign has comma within the string like below: "Adroup,Campaign,Impressions, Premiun Beer, Beer, Chicago, 1000" where the adgroup is "premium beer" and campaign is "Beer,Chicago". that will cause an issue if we parse this information by using comma. Does anyone know how to solve this problem?

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• Appropriate uses of Monad `fail` vs. MonadPlus `mzero`

  - by jberryman

  This is a question that has come up several times for me in the design code, especially libraries. There seems to be some interest in it so I thought it might make a good community wiki. The fail method in Monad is considered by some to be a wart; a somewhat arbitrary addition to the class that does not come from the original category theory. But of course in the current state of things, many Monad types have logical and useful fail instances. The MonadPlus class is a sub-class of Monad that provides an mzero method which logically encapsulates the idea of failure in a monad. So a library designer who wants to write some monadic code that does some sort of failure handling can choose to make his code use the fail method in Monad or restrict his code to the MonadPlus class, just so that he can feel good about using mzero, even though he doesn't care about the monoidal combining mplus operation at all. Some discussions on this subject are in this wiki page about proposals to reform the MonadPlus class. So I guess I have one specific question: What monad instances, if any, have a natural fail method, but cannot be instances of MonadPlus because they have no logical implementation for mplus? But I'm mostly interested in a discussion about this subject. Thanks! EDIT: One final thought occured to me. I recently learned (even though it's right there in the docs for fail) that monadic "do" notation is desugared in such a way that pattern match failures, as in (x:xs) <- return [] call the monad's fail. It seems like the language designers must have been strongly influenced by the prospect of some automatic failure handling built in to haskell's syntax in their inclusion of fail in Monad.

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• What C++ templates issue is going on with this error?

  - by WilliamKF

  Running gcc v3.4.6 on the Botan v1.8.8 I get the following compile time error building my application after successfully building Botan and running its self test: ../../src/Botan-1.8.8/build/include/botan/secmem.h: In member function `Botan::MemoryVector<T>& Botan::MemoryVector<T>::operator=(const Botan::MemoryRegion<T>&)': ../../src/Botan-1.8.8/build/include/botan/secmem.h:310: error: missing template arguments before '(' token What is this compiler error telling me? Here is a snippet of secmem.h that includes line 130: [...] /** * This class represents variable length buffers that do not * make use of memory locking. */ template<typename T> class MemoryVector : public MemoryRegion<T> { public: /** * Copy the contents of another buffer into this buffer. * @param in the buffer to copy the contents from * @return a reference to *this */ MemoryVector<T>& operator=(const MemoryRegion<T>& in) { if(this != &in) set(in); return (*this); } // This is line 130! [...]

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• MMGR Questions, code use and thread-saftey

  - by chadb

  1) Is MMGR thread safe? 2) I was hoping someone could help me understand some code. I am looking at something where a macro is used, but I don't understand the macro. I know it contains a function call and an if check, however, the function is a void function. How does wrapping "(m_setOwner (FILE,_LINE_,FUNCTION),false)" ever change return types? #define someMacro (m_setOwner(__FILE__,__LINE__,__FUNCTION__),false) ? NULL : new ... void m_setOwner(const char *file, const unsigned int line, const char *func); 3) What is the point of the reservoir? 4) On line 770 ("void *operator new(size_t reportedSize)" there is the line "// ANSI says: allocation requests of 0 bytes will still return a valid value" Who/what is ANSI in this context? Do they mean the standards? 5) This is more of C++ standards, but where does "reportedSize" come from for "void *operator new(size_t reportedSize)"? 6) Is this the code that is actually doing the allocation needed? "au-actualAddress = malloc(au-actualSize);"

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• Access to map data

  - by herzl shemuelian

  I have a complex map that defined typedef short short1 typedef short short2 typedef map<short1,short2> data_list; typedef map<string,list> table_list; I have a class that fill table_list class GroupingClass { table_list m_table_list; string Buildkey(OD e1){ string ostring; ostring+=string(e1.m_Date,sizeof(Date)); ostring+=string(e1.m_CT,sizeof(CT)); ostring+=string(e1.m_PT,sizeof(PT)); return ostring; } void operator() (const map<short1,short2>::value_type& myPair) { OptionsDefine e1=myPair.second; string key=Buildkey(e1); m_table_list[key][e1.m_short2]=e1.m_short2; } operator table_list() { return m_table_list; } }; and I use it by table_list TL2 GroupingClass gc; TL2=for_each(mapOD.begin(), mapOD.end(), gc); but when I try to access to internal map I have problems for example data_list tmp; tmp=TL2["AAAA"]; short i=tmp[1]; //I dont update i variable but if i use a loop by itrator this work properly why this no work at first way thanks herzl

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• Error using to_char // to_timetamp

  - by pepersview

  Hello, I have a database in PostgreSQL and I'm developing an application in PHP using this database. The problem is that when I execute the following query I get a nice result in phpPgAdmin but in my PHP application I get an error. The query: SELECT t.t_name, t.t_firstname FROM teachers AS t WHERE t.id_teacher IN (SELECT id_teacher FROM teacher_course AS tcourse JOIN course_timetable AS coursetime ON tcourse.course = coursetime.course AND to_char(to_timestamp('2010-4-12', 'YYYY-MM-DD'),'FMD') = (coursetime.day +1)) AND t.id_teacher NOT IN (SELECT id_teacher FROM teachers_fill WHERE date = '2010-4-12') ORDER BY t.t_name ASC And this is the error in PHP operator does not exist: text = integer (to_timestamp('', 'YYYY-MM-DD'),'FMD') = (courset... ^ HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts. The purpose to solve this error is to use the ORIGINAL query in php with : $date = "2010"."-".$selected_month."-".$selected_day; SELECT t.t_name, t.t_firstname FROM teachers AS t WHERE t.id_teacher IN (SELECT id_teacher FROM teacher_course AS tcourse JOIN course_timetable AS coursetime ON tcourse.course = coursetime.course AND to_char(to_timestamp('$date', 'YYYY-MM-DD'),'FMD') = (coursetime.day +1)) AND t.id_teacher NOT IN (SELECT id_teacher FROM teachers_fill WHERE date = '$date') ORDER BY t.t_name ASC

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• Evaluate an expression tree

  - by Phronima

  Hi, This project that I'm working on requires that an expression tree be constructed from a string of single digit operands and operators both represented as type char. I did the implmentation and the program up to that point works fine. I'm able to print out the inorder, preorder and postorder traversals in the correct way. The last part calls for evaulating the expression tree. The parameters are an expression tree "t" and its root "root". The expression tree is ((3+2)+(6+2)) which is equal to 13. Instead I get 11 as the answer. Clearly I'm missing something here and I've done everything short of bashing my head against the desk. I would greatly appreciate it if someone can point me in the right direction. (Note that at this point I'm only testing addition and will add in the other operators when I get this method working.) public int evalExpression( LinkedBinaryTree t, BTNode root ) { if( t.isInternal( root ) ) { int x = 0, y = 0, value = 0; char operator = root.element(); if( root.getLeft() != null ) x = evalExpression(t, t.left( root ) ); if( root.getRight() != null ) y = evalExpression(t, t.right( root ) ); if( operator == '+' ) { value = value + Character.getNumericValue(x) + Character.getNumericValue(y); } return value; } else { return root.element(); } }

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• Should I delete the string members of a C++ class?

  - by Bobby

  If I have the following declaration: #include <iostream> #include <string> class DEMData { private: int bitFldPos; int bytFldPos; std::string byteOrder; std::string desS; std::string engUnit; std::string oTag; std::string valType; int idx; public: DEMData(); DEMData(const DEMData &d); void SetIndex(int idx); int GetIndex() const; void SetValType(const char* valType); const char* GetValType() const; void SetOTag(const char* oTag); const char* GetOTag() const; void SetEngUnit(const char* engUnit); const char* GetEngUnit() const; void SetDesS(const char* desS); const char* GetDesS() const; void SetByteOrder(const char* byteOrder); const char* GetByteOrder() const; void SetBytFldPos(int bytFldPos); int GetBytFldPos() const; void SetBitFldPos(int bitFldPos); int GetBitFldPos() const; friend std::ostream &operator<<(std::ostream &stream, DEMData d); bool operator==(const DEMData &d) const; ~DEMData(); }; what code should be in the destructor? Should I "delete" the std::string fields?

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• Why strings behave like ValueType

  - by AJP

  I was perplexed after executing this piece of code, where strings seems to behave as if they are value types. I am wondering whether the assignment operator is operating on values like equality operator for strings. Here is the piece of code I did to test this behavior. using System; namespace RefTypeDelimma { class Program { static void Main(string[] args) { string a1, a2; a1 = "ABC"; a2 = a1; //This should assign a1 reference to a2 a2 = "XYZ"; //I expect this should change the a1 value to "XYZ" Console.WriteLine("a1:" + a1 + ", a2:" + a2);//Outputs a1:ABC, a2:XYZ //Expected: a1:XYZ, a2:XYZ (as string being a ref type) Proc(a2); //Altering values of ref types inside a procedure //should reflect in the variable thats being passed into Console.WriteLine("a1: " + a1 + ", a2: " + a2); //Outputs a1:ABC, a2:XYZ //Expected: a1:NEW_VAL, a2:NEW_VAL (as string being a ref type) } static void Proc(string Val) { Val = "NEW_VAL"; } } } In the above code if I use a custom classes instead of strings, I am getting the expected behavior. I doubt is this something to do with the string immutability? welcoming expert views on this.

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• Conversion between different template instantiation of the same template

  - by Naveen

  I am trying to write an operator which converts between the differnt types of the same implementation. This is the sample code: template <class T = int> class A { public: A() : m_a(0){} template <class U> operator A<U>() { A<U> u; u.m_a = m_a; return u; } private: int m_a; }; int main(void) { A<int> a; A<double> b = a; return 0; } However, it gives the following error for line u.m_a = m_a;. Error 2 error C2248: 'A::m_a' : cannot access private member declared in class 'A' d:\VC++\Vs8Console\Vs8Console\Vs8Console.cpp 30 Vs8Console I understand the error is because A<U> is a totally different type from A<T>. Is there any simple way of solving this (may be using a friend?) other than providing setter and getter methods? I am using Visual studio 2008 if it matters.

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• Threads are blocked in malloc and free, virtual size

  - by Albert Wang

  Hi, I'm running a 64-bit multi-threaded program on the windows server 2003 server (X64), It run into a case that some of the threads seem to be blocked in the malloc or free function forever. The stack trace is like follows: ntdll.dll!NtWaitForSingleObject() + 0xa bytes ntdll.dll!RtlpWaitOnCriticalSection() - 0x1aa bytes ntdll.dll!RtlEnterCriticalSection() + 0xb040 bytes ntdll.dll!RtlpDebugPageHeapAllocate() + 0x2f6 bytes ntdll.dll!RtlDebugAllocateHeap() + 0x40 bytes ntdll.dll!RtlAllocateHeapSlowly() + 0x5e898 bytes ntdll.dll!RtlAllocateHeap() - 0x1711a bytes MyProg.exe!malloc(unsigned __int64 size=0) Line 168 C MyProg.exe!operator new(unsigned __int64 size=1) Line 59 + 0x5 bytes C++ ntdll.dll!NtWaitForSingleObject() ntdll.dll!RtlpWaitOnCriticalSection() ntdll.dll!RtlEnterCriticalSection() ntdll.dll!RtlpDebugPageHeapFree() ntdll.dll!RtlDebugFreeHeap() ntdll.dll!RtlFreeHeapSlowly() ntdll.dll!RtlFreeHeap() MyProg.exe!free(void * pBlock=0x000000007e8e4fe0) C BTW, the param values passed to the new operator is not correct here maybe due to optimization. Also, at the same time, I found in the process Explorer, the virtual size of this program is 10GB, but the private bytes and working set is very small (<2GB). We did have some threads using virtualalloc but in a way that commit the memory in the call, and these threads are not blocked. m_pBuf = VirtualAlloc(NULL, m_size, MEM_COMMIT, PAGE_READWRITE); ...... VirtualFree(m_pBuf, 0, MEM_RELEASE); This looks strange to me, seems a lot of virtual space is reserved but not committed, and malloc/free is blocked by lock. I'm guessing if there's any corruptions in the memory/object, so plan to turn on gflag with pageheap to troubleshoot this. Does anyone has similar experience on this before? Could you share with me so I may get more hints? Thanks a lot!

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• C++ Template problem adding two data types

  - by Sara

  I have a template class with an overloaded + operator. This is working fine when I am adding two ints or two doubles. How do I get it to add and int and a double and return the double? template <class T> class TemplateTest { private: T x; public: TemplateTest<T> operator+(const TemplateTest<T>& t1)const { return TemplateTest<T>(x + t1.x); } } in my main function i have void main() { TemplateTest intTt1 = TemplateTest<int>(2); TemplateTest intTt2 = TemplateTest<int>(4); TemplateTest doubleTt1 = TemplateTest<double>(2.1d); TemplateTest doubleTt2 = TemplateTest<double>(2.5d); std::cout << intTt1 + intTt2 << /n; std::cout << doubleTt1 + doubleTt2 << /n; } I want to be able to also do this std::cout << doubleTt1 + intTt2 << /n;

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• std::map keys in C++

  - by Soumava

  I have a requirement to create two different maps in C++. The Key is of type CHAR * and the Value is a pointer to a struct. I am filling 2 maps with these pairs, in separate iterations. After creating both maps I need find all such instances in which the value of the string referenced by the CHAR * are same. For this i am using the following code : typedef struct _STRUCTTYPE { .. } STRUCTTYPE, *PSTRUCTTYPE; typedef pair {CHAR *,PSTRUCTTYPE} kvpair; .. CHAR *xyz; PSTRUCTTYPE abc; after filling the information; Map.insert (kvpair(xyz,abc)); the above is repeated x times for the first map, and y times for the second map. after both are filled out; std::map {CHAR *, PSTRUCTTYPE} :: iterator Iter,findIter; for (Iter=iteratedMap-begin();Iter!=iteratedMap-end();mapIterator++) { char *key = Iter-first; printf("%s\n",key); findIter=otherMap-find(key); //printf("%u",findIter-second); if (findIter!=otherMap-end()) { printf("Match!\n"); } } The above code does not show any match, although the list of keys in both maps show obvious matches. My understanding is that the equals operator for CHAR * just equates the memory address of the pointers. My question is, what should i do to alter the equals operator for this type of key or could I use a different datatype for the string? *note : {} has been used instead of angle brackets as the content inside angle brackets was not showing up in the post.

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• How to support comparisons for QVariant objects containing a custom type?

  - by Tyler McHenry

  According to the Qt documentation, QVariant::operator== does not work as one might expect if the variant contains a custom type: bool QVariant::operator== ( const QVariant & v ) const Compares this QVariant with v and returns true if they are equal; otherwise returns false. In the case of custom types, their equalness operators are not called. Instead the values' addresses are compared. How are you supposed to get this to behave meaningfully for your custom types? In my case, I'm storing an enumerated value in a QVariant, e.g. In a header: enum MyEnum { Foo, Bar }; Q_DECLARE_METATYPE(MyEnum); Somewhere in a function: QVariant var1 = QVariant::fromValue<MyEnum>(Foo); QVariant var2 = QVariant::fromValue<MyEnum>(Foo); assert(var1 == var2); // Fails! What do I need to do differently in order for this assertion to be true? I understand why it's not working -- each variant is storing a separate copy of the enumerated value, so they have different addresses. I want to know how I can change my approach to storing these values in variants so that either this is not an issue, or so that they do both reference the same underlying variable. It don't think it's possible for me to get around needing equality comparisons to work. The context is that I am using this enumeration as the UserData in items in a QComboBox and I want to be able to use QComboBox::findData to locate the item index corresponding to a particular enumerated value.

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• How to extract data from F# list

  - by David White

  Following up my previous question, I'm slowly getting the hang of FParsec (though I do find it particularly hard to grok). My next newbie F# question is, how do I extract data from the list the parser creates? For example, I loaded the sample code from the previous question into a module called Parser.fs, and added a very simple unit test in a separate module (with the appropriate references). I'm using XUnit: open Xunit [<Fact>] let Parse_1_ShouldReturnListContaining1 () = let interim = Parser.parse("1") Assert.False(List.isEmpty(interim)) let head = interim.Head // I realise that I have only one item in the list this time Assert.Equal("1", ???) Interactively, when I execute parse "1" the response is: val it : Element list = [Number "1"] and by tweaking the list of valid operators, I can run parse "1+1" to get: val it : Element list = [Number "1"; Operator "+"; Number "1"] What do I need to put in place of my ??? in the snippet above? And how do I check that it is a Number, rather than an Operator, etc.?

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• Using a variable in a mysql query, in a C++ MFC program.

  - by D.Gaughan

  Hi, after extensive trawling of the internet I still havent found any solution for this problem. I`m writing a small C++ app that connects to an online database and outputs the data in a listbox. I need to enable a search function using an edit box, but I cant get the query to work while using a variable. My code is: res = mysql_perform_query (conn, "select distinct artist from Artists"); //res = mysql_perform_query (conn, "select album from Artists where artist = ' ' "); while((row = mysql_fetch_row(res)) != NULL){ CString str; UpdateData(); str = ("%s\n", row[0]); UpdateData(FALSE); m_list_control.AddString(str); } the first "res = " line is working fine, but I need the second one to work. I have a member variable m_search_edit set up for the edit box, but any way I try to include it in the sql statement causes errors. eg. res = mysql_perform_query (conn, "select album from Artists where artist = '"+m_search_edit+" ' "); causes this error: error C2664: 'mysql_perform_query' : cannot convert parameter 2 from 'class CString' to 'char *' No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called" And when I convert m_search_edit to a char* it gives me a " Cannot add 2 pointers" error. Any way around this???

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• How to differentiate between exceptions i can show the user, and ones i can't?

  - by Ian Boyd

  i have some business logic that traps some logically invalid situations, e.g. trying to reverse a transaction that was already reversed. In this case the correct action is to inform the user: Transaction already reversed or Cannot reverse a reversing transaction or You do not have permission to reverse transactions or This transaction is on a session that has already been closed or This transaction is too old to be reversed The question is, how do i communicate these exceptional cases back to the calling code, so they can show the user? Do i create a separate exception for each case: catch (ETransactionAlreadyReversedException) MessageBox.Show('Transaction already reversed') catch (EReversingAReversingTransactionException) MessageBox.Show('Cannot reverse a reversing transaction') catch (ENoPermissionToReverseTranasctionException) MessageBox.Show('You do not have permission to reverse transactions') catch (ECannotReverseTransactionOnAlredyClosedSessionException) MessageBox.Show('This transaction is on a session that has already been closed') catch (ECannotReverseTooOldTransactionException) MessageBox.Show('This transaction is too old to be reversed') Downside for this is that when there's a new logical case to show the user: Tranasctions created by NSL cannot be reversed i don't simply show the user a message, and instead it leaks out as an unhandled excpetion, when really it should be handled with another MessageBox. The alternative is to create a single exception class: `EReverseTransactionException` With the understanding that any exception of this type is a logical check, that should be handled with a message box: catch (EReverseTransactionException) But it's still understood that any other exceptions, ones that involve, for example, an memory ECC parity error, continue unhandled. In other words, i don't convert all errors that can be thrown by the ReverseTransaction() method into EReverseTransactionException, only ones that are logically invalid cause of the user.

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• PHP: Three item validation comparison

  - by DavidYell

  I have 3 featured product panels on the homepage, and I'm writing a CMS page for it. I'm trying to validate the items. They are selected via three <select> elements, featured1, featured2 and featured3. The default is <option value="0" selected>Select an element</option> I need to validate the $_POST to ensure that the user hasn't selected the same product for more than one of the panels. I have worked out that each $_POST needs to be $_POST['featuredN'] > 0 but I can't seem to find a logical way of processing the 7 potential outcomes. Using a logic table, where 1 is a set value. 1 2 3 ------- 0 0 0 1 1 1 1 0 0 0 1 0 0 0 1 1 1 0 0 1 1 If an item is 0, then I will not update it, but I want the user to be able to update a single item if needs be. I cannot find a logical way to see if the item is not 0, and then compare it to another item if that also is not 0. So far my colleague suggested, adding up the values. Which works to see if condition 1 0 0 0 is not met. I have a vague feeling that some form of recursive function might be in order, but I can't quite get my brain to help me on this one! So to the collective brain! :)

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• Compare two variant with boost static_visitor

  - by Zozzzzz

  I started to use the boost library a few days ago so my question is maybe trivial. I want to compare two same type variants with a static_visitor. I tried the following, but it don't want to compile. struct compare:public boost::static_visitor<bool> { bool operator()(int& a, int& b) const { return a<b; } bool operator()(double& a, double& b) const { return a<b; } }; int main() { boost::variant<double, int > v1, v2; v1 = 3.14; v2 = 5.25; compare vis; bool b = boost::apply_visitor(vis, v1,v2); cout<<b; return 0; } Thank you for any help or suggestion!

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• Creating simple calculator with bison & flex in C++ (not C)

  - by ak91

  Hey, I would like to create simple C++ calculator using bison and flex. Please note I'm new to the creating parsers. I already found few examples in bison/flex but they were all written in C. My goal is to create C++ code, where classes would contain nodes of values, operations, funcs - to create AST (evaluation would be done just after creating whole AST - starting from the root and going forward). For example: my_var = sqrt(9 ** 2 - 32) + 4 - 20 / 5 my_var * 3 Would be parsed as: = / \ my_var + / \ sqrt - | / \ - 4 / / \ / \ ** 32 20 5 / \ 9 2 and the second AST would look like: * / \ my_var 3 Then following pseudocode reflects AST: ast_root = create_node('=', new_variable("my_var"), exp) where exp is: exp = create_node(OPERATOR, val1, val2) but NOT like this: $$ = $1 OPERATOR $3 because this way I directly get value of operation instead of creation the Node. I believe the Node should contain type (of operation), val1 (Node), val2 (Node). In some cases val2 would be NULL, like above mentioned sqrt which takes in the end one argument. Right? It will be nice if you can propose me C++ skeleton (without evaluation) for above described problem (including *.y file creating AST) to help me understand the way of creating/holding Nodes in AST. Code can be snipped, just to let me get the idea. I'll also be grateful if you point me to an existing (possibly simple) example if you know any. Thank you all for your time and assistance!

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• Advice on Minimizing Stored Procedure Parameters

  - by RPM1984

  Hi Guys, I have an ASP.NET MVC Web Application that interacts with a SQL Server 2008 database via Entity Framework 4.0. On a particular page, i call a stored procedure in order to pull back some results based on selections on the UI. Now, the UI has around 20 different input selections, ranging from a textbox, dropdown list, checkboxes, etc. Each of those inputs are "grouped" into logical sections. Example: Search box : "Foo" Checkbox A1: ticked, Checkbox A2: unticked Dropdown A: option 3 selected Checkbox B1: ticked, Checkbox B2: ticked, Checkbox B3: unticked So i need to call the SPROC like this: exec SearchPage_FindResults @SearchQuery = 'Foo', @IncludeA1 = 1, @IncludeA2 = 0, @DropDownSelection = 3, @IncludeB1 = 1, @IncludeB2 = 1, @IncludeB3 = 0 The UI is not too important to this question - just wanted to give some perspective. Essentially, i'm pulling back results for a search query, filtering these results based on a bunch of (optional) selections a user can filter on. Now, My questions/queries: What's the best way to pass these parameters to the stored procedure? Are there any tricks/new ways (e.g SQL Server 2008) to do this? Special "table" parameters/arrays - can we pass through User-Defined-Types? Keep in mind im using Entity Framework 4.0 - but could always use classic ADO.NET for this if required. What about XML? What are the serialization/de-serialization costs here? Is it worth it? How about a parameter for each logical section? Comma-seperated perhaps? Just thinking out loud. This page is particulary important from a user point of view, and needs to perform really well. The stored procedure is already heavy in logic, so i want to minimize the performance implications - so keep that in mind. With that said - what is the best approach here?

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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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• SFINAE and detecting if a C++ function object returns void.

  - by Tom Swirly

  I've read the various authorities on this, include Dewhurst and yet haven't managed to get anywhere with this seemingly simple question. What I want to do is to call a C++ function object, (basically, anything you can call, a pure function or a class with ()), and return its value, if that is not void, or "true" otherwise. #include <stdio.h> struct Foo { void operator()() {} }; struct Bar { bool operator()() { return false; } }; Foo foo; Bar bar; bool baz() { return false; } void bang() {} const char* print(bool b) { printf(b ? "true, " : "false, "); } template <typename Functor> bool magicCallFunction(Functor f) { return true; // lots of template magic occurs here... } int main(int argc, char** argv) { print(magicCallFunction(foo)); print(magicCallFunction(bar)); print(magicCallFunction(baz)); print(magicCallFunction(bang)); printf("\n"); }

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