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• Strange - Clicking Update button doesn’t cause a postback due to <!-- tag

  - by AspOnMyNet

  If I define the following template inside DetailsView, then upon clicking an Update or Insert button, the page is posted back to the server: <EditItemTemplate> <asp:TextBox ID="txtDate" runat="server" Text='<%# Bind("Date") %>'></asp:TextBox> <asp:CompareValidator ID="valDateType" runat="server" ControlToValidate="txtDate" Type="Date" Operator="DataTypeCheck" Display="Dynamic" >*</asp:CompareValidator> </EditItemTemplate> If I remove CompareValidator control from the above code by simply deleting it, then page still gets posted back.But if instead I remove CompareValidator control by enclosing it within <!-- --> tags, then for some reason clicking an Update or Insert button doesn’t cause a postback...instead nothing happens: <EditItemTemplate> <asp:TextBox ID="txtDate" runat="server" Text='<%# Bind("Date") %>'></asp:TextBox> <!-- <asp:CompareValidator ID="valDateType" runat="server" ControlToValidate="txtDate" Type="Date" Operator="DataTypeCheck" Display="Dynamic" >*</asp:CompareValidator> --> </EditItemTemplate> </EditItemTemplate> Any idea why page doesn't get posted back? thanx

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• Model Binding, a simple, simple question

  - by Paul Hatcherian

  I have a struct which works much like the System.Nullable type: public struct SpecialProperty<T> { public static implicit operator T(SpecialProperty<T> value) { return value.Value; } public static implicit operator SpecialProperty<T>(T value) { return new TrackChanges<T> { Value = value }; } T internalValue; public T Value { get { return internalValue; } set { internalValue = value; } } public override bool Equals(object other) { return Value.Equals(other); } public override int GetHashCode() { return Value.GetHashCode(); } public override string ToString() { return Value.ToString(); } } I'm trying to use it with ASP.NET MVC binding. Using the default customer model binder the property will always yield null. I can fix this by adding ".Value" to the end of every form input name, but I just want it to bind to the new type directly using some sort of custom model binder, but all the solutions I've tried seemed needlessly complex. I feel like I should be able to extend the default binder and with a few lines of code redirect the property binding to the entire model using implicit conversion. I don't quite get the binding paradigm of the default binder, but it seems really stuck on this distinction between the model and model properties. What is the simplest method to do this? Thanks!

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• trouble with algorithm

  - by rebel_UA

  David likes number of estimates with base "k" and not a multiple(a%2!=0) of the number of zeros at the end. Set system and the number of the order and print it I need to optimi this algoritm: class David{ private: int k; public: David(); David(int); int operator[] (int); }; David::David(){ k=10; }; David::David(int k){ this->k=k; } int David::operator[] (int n){ int q; int p; int i=1; for(int r=0;r<n;i++){ q=0; p=i; for(;;){ if(p%k) break; if(p==0) break; ++q; p/=k; } if(q%2){ r++; } } return i-1; }

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• Am I deleting this properly?

  - by atch

  I have some struct: struct A { const char* name_; A* left_; A* right_; A(const char* name):name_(name), left_(nullptr), right_(nullptr){} A(const A&); //A(const A*);//ToDo A& operator=(const A&); ~A() { /*ToDo*/ }; }; /*Just to compile*/ A& A::operator=(const A& pattern) { //check for self-assignment if (this != &pattern) { void* p = new char[sizeof(A)]; } return *this; } A::A(const A& pat) { void* p = new char[sizeof(A)]; A* tmp = new (p) A("tmp"); tmp->~A(); delete tmp;//I WONDER IF HERE I SHOULD USE DIFFERENT delete[]? } int _tmain(int argc, _TCHAR* argv[]) { A a("a"); A b = a; cin.get(); return 0; } Guys I know this is far from ideal and far from finished. But please don't tell me the answer how to do it properly. I'm trying to figure it out myself. The only think I would like to know if I'm deleting my memory in proper way. Thanks.

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• Adding Functions to an Implementation of Vector

  - by Meursault

  I have this implementation of vector that I've been working on for a few days using examples from a textbook: #include <iostream> #include <string> #include <cassert> #include <algorithm> #include <cstring> // Vector.h using namespace std; template <class T> class Vector { public: typedef T * iterator; Vector(); Vector(unsigned int size); Vector(unsigned int size, const T & initial); Vector(const Vector<T> & v); // copy constructor ~Vector(); unsigned int capacity() const; // return capacity of vector (in elements) unsigned int size() const; // return the number of elements in the vector bool empty() const; iterator begin(); // return an iterator pointing to the first element iterator end(); // return an iterator pointing to one past the last element T & front(); // return a reference to the first element T & back(); // return a reference to the last element void push_back(const T & value); // add a new element void pop_back(); // remove the last element void reserve(unsigned int capacity); // adjust capacity void resize(unsigned int size); // adjust size void erase(unsigned int size); // deletes an element from the vector T & operator[](unsigned int index); // return reference to numbered element Vector<T> & operator=(const Vector<T> &); private: unsigned int my_size; unsigned int my_capacity; T * buffer; }; template<class T>// Vector<T>::Vector() { my_capacity = 0; my_size = 0; buffer = 0; } template<class T> Vector<T>::Vector(const Vector<T> & v) { my_size = v.my_size; my_capacity = v.my_capacity; buffer = new T[my_size]; for (int i = 0; i < my_size; i++) buffer[i] = v.buffer[i]; } template<class T>// Vector<T>::Vector(unsigned int size) { my_capacity = size; my_size = size; buffer = new T[size]; } template<class T>// Vector<T>::Vector(unsigned int size, const T & initial) { my_size = size; //added = size my_capacity = size; buffer = new T [size]; for (int i = 0; i < size; i++) buffer[i] = initial; } template<class T>// Vector<T> & Vector<T>::operator = (const Vector<T> & v) { delete[ ] buffer; my_size = v.my_size; my_capacity = v.my_capacity; buffer = new T [my_size]; for (int i = 0; i < my_size; i++) buffer[i] = v.buffer[i]; return *this; } template<class T>// typename Vector<T>::iterator Vector<T>::begin() { return buffer; } template<class T>// typename Vector<T>::iterator Vector<T>::end() { return buffer + size(); } template<class T>// T& Vector<T>::Vector<T>::front() { return buffer[0]; } template<class T>// T& Vector<T>::Vector<T>::back() { return buffer[size - 1]; } template<class T> void Vector<T>::push_back(const T & v) { if (my_size >= my_capacity) reserve(my_capacity +5); buffer [my_size++] = v; } template<class T>// void Vector<T>::pop_back() { my_size--; } template<class T>// void Vector<T>::reserve(unsigned int capacity) { if(buffer == 0) { my_size = 0; my_capacity = 0; } if (capacity <= my_capacity) return; T * new_buffer = new T [capacity]; assert(new_buffer); copy (buffer, buffer + my_size, new_buffer); my_capacity = capacity; delete[] buffer; buffer = new_buffer; } template<class T>// unsigned int Vector<T>::size()const { return my_size; } template<class T>// void Vector<T>::resize(unsigned int size) { reserve(size); my_size = size; } template<class T>// T& Vector<T>::operator[](unsigned int index) { return buffer[index]; } template<class T>// unsigned int Vector<T>::capacity()const { return my_capacity; } template<class T>// Vector<T>::~Vector() { delete[]buffer; } template<class T> void Vector<T>::erase(unsigned int size) { } int main() { Vector<int> v; v.reserve(2); assert(v.capacity() == 2); Vector<string> v1(2); assert(v1.capacity() == 2); assert(v1.size() == 2); assert(v1[0] == ""); assert(v1[1] == ""); v1[0] = "hi"; assert(v1[0] == "hi"); Vector<int> v2(2, 7); assert(v2[1] == 7); Vector<int> v10(v2); assert(v10[1] == 7); Vector<string> v3(2, "hello"); assert(v3.size() == 2); assert(v3.capacity() == 2); assert(v3[0] == "hello"); assert(v3[1] == "hello"); v3.resize(1); assert(v3.size() == 1); assert(v3[0] == "hello"); Vector<string> v4 = v3; assert(v4.size() == 1); assert(v4[0] == v3[0]); v3[0] = "test"; assert(v4[0] != v3[0]); assert(v4[0] == "hello"); v3.pop_back(); assert(v3.size() == 0); Vector<int> v5(7, 9); Vector<int>::iterator it = v5.begin(); while (it != v5.end()) { assert(*it == 9); ++it; } Vector<int> v6; v6.push_back(100); assert(v6.size() == 1); assert(v6[0] == 100); v6.push_back(101); assert(v6.size() == 2); assert(v6[0] == 100); v6.push_back(101); cout << "SUCCESS\n"; } So far it works pretty well, but I want to add a couple of functions to it that I can't find examples for, a SWAP function that would look at two elements of the vector and switch their values and and an ERASE function that would delete a specific value or range of values in the vector. How should I begin implementing the two extra functions?

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• LINQ - is SkipWhile broken?

  - by Judah Himango

  I'm a bit surprised to find the results of the following code, where I simply want to remove all 3s from a sequence of ints: var sequence = new [] { 1, 1, 2, 3 }; var result = sequence.SkipWhile(i => i == 3); // Oh noes! Returns { 1, 1, 2, 3 } Why isn't 3 skipped? My next thought was, OK, the Except operator will do the trick: var sequence = new [] { 1, 1, 2, 3 }; var result = sequence.Except(i => i == 3); // Oh noes! Returns { 1, 2 } In summary, Except removes the 3, but also removes non-distinct elements. Grr. SkipWhile doesn't skip the last element, even if it matches the condition. Grr. Can someone explain why SkipWhile doesn't skip the last element? And can anyone suggest what LINQ operator I can use to remove the '3' from the sequence above?

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• InvalidCastException in DataGridView

  - by Max Yaffe

  (Using VS 2010 Beta 2 - .Net 4.0 B2 Rel) I have a class, MyTable, derived from BindingList where S is a struct. S is made up of several other structs, for example: public class MyTable<S>:BindingList<S> where S: struct { ... } public struct MyStruct { public MyReal r1; public MyReal r2; public MyReal R1 {get{...} set{...}} public MyReal R2 {get{...} set{...}} ... } public struct MyReal { private Double d; private void InitFromString(string) {this.d = ...;} public MyReal(Double d) { this.d = d;} public MyReal(string val) { this.d = default(Double); InitFromString(val);} public override string ToString() { return this.real.ToString();} public static explicit operator MyReal(string s) { return new MyReal(s);} public static implicit operator String(MyReal r) { return r.ToString();} ... } OK, I use the MyTable as a binding source for a DataGridView. I can load the data grid easily using InitFromString on individual fields in MyStruct. The problem comes when I try to edit a value in a cell of the DataGridView. Going to the first row, first column, I change the value of the existing number. It gives an exception blizzard, the first line of which says: System.FormatException: Invalid cast from 'System.String' to 'MyReal' I've looked at the casting discussions and reference books but don't see any obvious problems. Any ideas?

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• Possible mem leak?

  - by LCD Fire

  I'm new to the concept so don't be hard on me. why doesn't this code produce a destructor call ? The names of the classes are self-explanatory. The SString will print a message in ~SString(). It only prints one destructor message. int main(int argc, TCHAR* argv[]) { smart_ptr<SString> smt(new SString("not lost")); new smart_ptr<SString>(new SString("but lost")); return 0; } Is this a memory leak? The impl. for smart_ptr is from here edited: //copy ctor smart_ptr(const smart_ptr<T>& ptrCopy) { m_AutoPtr = new T(ptrCopy.get()); } //overloading = operator smart_ptr<T>& operator=(smart_ptr<T>& ptrCopy) { if(m_AutoPtr) delete m_AutoPtr; m_AutoPtr = new T(*ptrCopy.get()); return *this; }

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• Why doesn't Perl file glob() work outside of a loop in scalar context?

  - by Rob

  According to the Perl documentation on file globbing, the <*> operator or glob() function, when used in a scalar context, should iterate through the list of files matching the specified pattern, returning the next file name each time it is called or undef when there are no more files. But, the iterating process only seems to work from within a loop. If it isn't in a loop, then it seems to start over immediately before all values have been read. From the Perl docs: In scalar context, glob iterates through such filename expansions, returning undef when the list is exhausted. http://perldoc.perl.org/functions/glob.html However, in scalar context the operator returns the next value each time it's called, or undef when the list has run out. http://perldoc.perl.org/perlop.html#I/O-Operators Example code: use warnings; use strict; my $filename; # in scalar context, <*> should return the next file name # each time it is called or undef when the list has run out $filename = <*>; print "$filename\n"; $filename = <*>; # doesn't work as documented, starts over and print "$filename\n"; # always returns the same file name $filename = <*>; print "$filename\n"; print "\n"; print "$filename\n" while $filename = <*>; # works in a loop, returns next file # each time it is called In a directory with 3 files...file1.txt, file2.txt, and file3.txt, the above code will output: file1.txt file1.txt file1.txt file1.txt file2.txt file3.txt Note: The actual perl script should be outside the test directory, or you will see the file name of the script in the output as well. Am I doing something wrong here, or is this how it is supposed to work?

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• Template with constant expression: error C2975 with VC++2008

  - by Arman

  Hello, I am trying to use elements of meta programming, but hit the wall with the first trial. I would like to have a comparator structure which can be used as following: intersect_by<ID>(L1.data, L2.data, "By ID: "); intersect_by<IDf>(L1.data, L2.data, "By IDf: "); Where: struct ID{};// Tag used for original IDs struct IDf{};// Tag used for the file position //following Boost.MultiIndex examples template<typename Tag,typename MultiIndexContainer> void intersect_by( const MultiIndexContainer& L1,const MultiIndexContainer& L2,std::string msg, Tag* =0 /* fixes a MSVC++ 6.0 bug with implicit template function parms / ) { / obtain a reference to the index tagged by Tag */ const typename boost::multi_index::index<MultiIndexContainer,Tag>::type& L1_ID_index= get<Tag>(L1); const typename boost::multi_index::index<MultiIndexContainer,Tag>::type& L2_ID_index= get<Tag>(L2); std::set_intersection( L1_ID_index.begin(), L1_ID_index.end(), L2_ID_index.begin(), L2_ID_index.end(), std::inserter(s, s.begin()), strComparator() // Here I get the C2975 error ); } template<int N> struct strComparator; template<> struct strComparator<0>{ bool operator () (const particleID& id1, const particleID& id2) const { return id1.ID struct strComparator<1{ bool operator () (const particleID& id1, const particleID& id2) const { return id1.IDf }; What I am missing? kind regards Arman.

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• Rename a file with perl

  - by perlnoob

  I have a file in a different folder I want to rename in perl, I was looking at a solution earlier that showed something like this: for (<backup.rar>) { my $file = $_; my $new = $_ 'backup'. @test .'.rar'; rename $file, $new or die "Error, can not rename $file as $new: $!"; } however backup.rar is in a different folder, I did try putting "C:\backup\backup.rar" in the < above, however I got the same error. C:\Program Files\WinRARperl backup.pl String found where operator expected at backup.pl line 35, near "$_ 'backup'" (Missing operator before 'backup'?) syntax error at backup.pl line 35, near "$_ 'backup'" Execution of backup.pl aborted due to compilation errors. I was using # Get time my @test = POSIX::strftime("%m-%d-%Y--%H-%M-%S\n", localtime); print @test; To get the current time, however I couldn't seem to get it to rename correctly. What can I do to fix this? Please note I am doing this on a windows box.

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• Function that prints something to std::ostream and returns std::ostream?

  - by dehmann

  I want to write a function that outputs something to a ostream that's passed in, and return the stream, like this: std::ostream& MyPrint(int val, std::ostream* out) { *out << val; return *out; } int main(int argc, char** argv){ std::cout << "Value: " << MyPrint(12, &std::cout) << std::endl; return 0; } It would be convenient to print the value like this and embed the function call in the output operator chain, like I did in main(). It doesn't work, however, and prints this: $ ./a.out 12Value: 0x6013a8 The desired output would be this: Value: 12 How can I fix this? Do I have to define an operator<< instead? UPDATE: Clarified what the desired output would be. UPDATE2: Some people didn't understand why I would print a number like that, using a function instead of printing it directly. This is a simplified example, and in reality the function prints a complex object rather than an int.

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• What is the point of the logical operators in C?

  - by reubensammut

  I was just wondering if there is an XOR logical operator in C (something like && for AND but for XOR). I know I can split an XOR into ANDs, NOTs and ORs but a simple XOR would be much better. Then it occurred to me that if I use the normal XOR bitwise operator between two conditions, it might just work. And for my tests it did. Consider: int i = 3; int j = 7; int k = 8; Just for the sake of this rather stupid example, if I need k to be either greater than i or greater than j but not both, XOR would be quite handy. if ((k > i) XOR (k > j)) printf("Valid"); else printf("Invalid"); or printf("%s",((k > i) XOR (k > j)) ? "Valid" : "Invalid"); I put the bitwise XOR ^ and it produced "Invalid". Putting the results of the two comparisons in two integers resulted in the 2 integers to contain a 1, hence the XOR produced a false. I've then tried it with the & and | bitwise operators and both gave the expected results. All this makes sense knowing that true conditions have a non zero value, whilst false conditions have zero values. I was wondering, is there a reason to use the logical && and || when the bitwise operators &, | and ^ work just the same? Thanks Reuben

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• Can a function return an object? Objective-C and NSMutableArray

  - by seaworthy

  I have an NSMutableArray. It's members eventually become members of an array instance in a class. I want to put the instantiantion of NSMutable into a function and to return an array object. If I can do this, I can make some of my code easier to read. Is this possible? Here is what I am trying to figure out. //Definition: > function Objects (float a, float b) { > NSMutableArray *array = [[NSMutableArray alloc] init]; > [array addObject:[NSNumber numberWithFloat:a]]; > [array addObject:[NSNumber numberWithFloat:b]]; > //[release array]; ???????? return array; > } //Declaration: Math *operator = [[Math alloc] init]; [operator findSum:Objects(20.0,30.0)]; My code compiles if I instantiate NSMutableArray right before I send the message to the receiver. I know I can have an array argument along with the method. What I have problem seeing is how to use a function and to replace the argument with a function call. Any help is appreciated. I am interested in the concept not in suggestions to replace the findSum method.

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• Is it okay to implement reference counting through composition?

  - by Billy ONeal

  Most common re-usable reference counted objects use private inheritance to implement re-use. I'm not a huge fan of private inheritance, and I'm curious if this is an acceptable way of handling things: class ReferenceCounter { std::size_t * referenceCount; public: ReferenceCounter() : referenceCount(NULL) {}; ReferenceCounter(ReferenceCounter& other) : referenceCount(other.referenceCount) { if (!referenceCount) { referenceCount = new std::size_t(1); other.referenceCount = referenceCount; } else { ++(*referenceCount); } }; ReferenceCounter& operator=(const ReferenceCounter& other) { ReferenceCounter temp(other); swap(temp); return *this; }; void swap(ReferenceCounter& other) { std::swap(referenceCount, other.referenceCount); }; ~ReferenceCounter() { if (referenceCount) { --(*referenceCount); if (!*referenceCount) delete referenceCount; } }; operator bool() const { return referenceCount && (*referenceCount != 0); }; }; class SomeClientClass { HANDLE someHandleThingy; ReferenceCounter objectsStillActive; public: SomeClientClass() { //Construct handle thingy } ~SomeClientClass() { if (objectsStillActive) return; //Release resources }; }; or are there subtle problems with this I'm not seeing?

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• Changing associativity

  - by Sorush Rabiee

  Hi... The associativity of stream insertion operator is rtl, forgetting this fact sometimes cause to runtime or logical errors. for example: 1st- int F() { static int internal_counter c=0; return ++c; } in the main function: //....here is main() cout<<”1st=”<<F()<<”,2nd=”<<F()<<”,3rd=”<<F(); and the output is: 1st=3,2nd=2,3rd=1 that is different from what we expect at first look. 2nd- suppose that we have an implementation of stack data structure like this: // //... a Stack<DataType> class …… // Stack<int> st(10); for(int i=1;i<11;i++) st.push(i); cout<<st.pop()<<endl<<st.pop()<<endl<<st.pop()<<endl<<st.pop()<<endl; expected output is something like: 10 9 8 7 but we have: 7 8 9 10 There is no internal bug of << implementation but it can be so confusing... and finally[:-)] my question: is there any way to change assocativity of an operator by overloading it?

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• restrict documents for mapreduce with mongoid

  - by theBernd

  I implemented the pearson product correlation via map / reduce / finalize. The missing part is to restrict the documents (representing users) to be processed via a filter query. For a simple query like mapreduce(mapper, reducer, :finalize => finalizer, :query => { :name => 'Bernd' }) I get this to work. But my filter criteria is a little bit more complicated: I have one set of preferences which need to have at least one common element and another set of preferences which may not have a common element. In a later step I also want to restrict this to documents (users) within a certain geographical distance. Currently I have this code working in my map function, but I would prefer to separate this into either query params as supported by mongoid or a javascript function. All my attempts to solve this failed since the code is either ignored or raises an error. I did a couple of tests. A regular find like User.where(:name.in => ['Arno', 'Bernd', 'Claudia']) works and returns #<Mongoid::Criteria:0x00000101f0ea40 @selector={:name=>{"$in"=>["Arno", "Bernd", "Claudia"]}}, @options={}, @klass=User, @documents=[]> Trying the same with mapreduce User.collection. mapreduce(mapper, reducer, :finalize => finalizer, :query => { :name.in => ['Arno', 'Bernd', 'Claudia'] }) fails with `serialize': keys must be strings or symbols (TypeError) in bson-1.1.5 The intermediate query parameter looks like this :query=>{#<Mongoid::Criterion::Complex:0x00000101a209e8 @key=:name, @operator="in">=>["Arno", "Bernd", "Claudia"]} and at least @operator looks a bit weird to me. I'm also uncertain if the class name can be omitted. BTW - I'm using mongodb 1.6.5-x86_64, and the mongoid 2.0.0.beta.20, mongo 1.1.5 and bson 1.1.5 gems on MacOS. What am I doing wrong? Thanks in advance.

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• C++ error: expected initializer before ‘&’ token

  - by Werner

  Hi, the following piece of C++ code compiled two years ago in a suse 10.1 Linux machine. #ifndef DATA_H #define DATA_H #include <iostream> #include <iomanip> inline double sqr(double x) { return x*x; } enum Direction { X,Y,Z }; inline Direction next(const Direction d) { switch(d) { case X: return Y; case Y: return Z; case Z: return X; } } inline ostream& operator<<(ostream& os,const Direction d) { switch(d) { case X: return os << "X"; case Y: return os << "Y"; case Z: return os << "Z"; } } ... ... Now, I am trying to compile it on Ubuntu 9.10 and I get the error: data.h:20: error: expected initializer before ‘&’ token which is referred to the line of: inline ostream& operator<<(ostream& os,const Direction d) the g++ used on this machine is: Using built-in specs. Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.1-4ubuntu9' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --disable-werror --with-arch-32=i486 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.4.1 (Ubuntu 4.4.1-4ubuntu9) Could you give me some hint about this error? Thanks

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• Internal "Tee" setup

  - by RadlyEel

  I have inherited some really old VC6.0 code that I am upgrading to VS2008 for building a 64-bit app. One required feature that was implemented long, long ago is overriding std::cout so its output goes simultaneously to a console window and to a file. The implementation depended on the then-current VC98 library implementation of ostream and, of course, is now irretrievably broken with VS2008. It would be reasonable to accumulate all the output until program termination time and then dump it to a file. I got part of the way home by using freopen(), setvbuf(), and ios::sync_with_stdio(), but to my dismay, the internal library does not treat its buffer as a ring buffer; instead when it flushes to the output device it restarts at the beginning, so every flush wipes out all my accumulated output. Converting to a more standard logging function is not desirable, as there are over 1600 usages of "std::cout << " scattered throughout almost 60 files. I have considered overriding ostream's operator<< function, but I'm not sure if that will cover me, since there are global operator<< functions that can't be overridden. (Or can they?) Any ideas on how to accomplish this?

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• linux new/delete, malloc/free large memory blocks

  - by brian_mk

  Hi folks, We have a linux system (kubuntu 7.10) that runs a number of CORBA Server processes. The server software uses glibc libraries for memory allocation. The linux PC has 4G physical memory. Swap is disabled for speed reasons. Upon receiving a request to process data, one of the server processes allocates a large data buffer (using the standard C++ operator 'new'). The buffer size varies depening upon a number of parameters but is typically around 1.2G Bytes. It can be up to about 1.9G Bytes. When the request has completed, the buffer is released using 'delete'. This works fine for several consecutive requests that allocate buffers of the same size or if the request allocates a smaller size than the previous. The memory appears to be free'd ok - otherwise buffer allocation attempts would eventually fail after just a couple of requests. In any case, we can see the buffer memory being allocated and freed for each request using tools such as KSysGuard etc. The problem arises when a request requires a buffer larger than the previous. In this case, operator 'new' throws an exception. It's as if the memory that has been free'd from the first allocation cannot be re-allocated even though there is sufficient free physical memory available. If I kill and restart the server process after the first operation, then the second request for a larger buffer size succeeds. i.e. killing the process appears to fully release the freed memory back to the system. Can anyone offer an explanation as to what might be going on here? Could it be some kind of fragmentation or mapping table size issue? I am thinking of replacing new/delete with malloc/free and use mallopt to tune the way the memory is being released to the system. BTW - I'm not sure if it's relevant to our problem, but the server uses Pthreads that get created and destroyed on each processing request. Cheers, Brian.

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• Weird bug with C++ lambda expressions in VS2010

  - by Andrei Tita

  In a couple of my projects, the following code: class SmallClass { public: int x1, y1; void TestFunc() { auto BadLambda = [&]() { int g = x1 + 1; //ok int h = y1 + 1; //c2296 int l = static_cast<int>(y1); //c2440 }; int y1_copy = y1; //it works if you create a local copy auto GoodLambda = [&]() { int h = y1_copy + 1; //ok int l = this->y1 + 1; //ok }; } }; generates error C2296: '+' : illegal, left operand has type 'double (__cdecl *)(double)' or alternatively error C2440: 'static_cast' : cannot convert from 'double (__cdecl *)(double)' to 'int' You get the picture. It also happens if catching by value. The error seems to be tied to the member name "y1". It happened in different classes, different projects and with (seemingly) any type for y1; for example, this code: [...] MyClass y1; void TestFunc() { auto BadLambda = [&]()->void { int l = static_cast<int>(y1); //c2440 }; } generates both these errors: error C2440: 'static_cast' : cannot convert from 'MyClass' to 'int' No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called error C2440: 'static_cast' : cannot convert from 'double (__cdecl *)(double)' to 'int' There is no context in which this conversion is possible It didn't, however, happen in a completely new project. I thought maybe it was related to Lua (the projects where I managed to reproduce this bug both used Lua), but I did not manage to reproduce it in a new project linking Lua. It doesn't seem to be a known bug, and I'm at a loss. Any ideas as to why this happens? (I don't need a workaround; there are a few in the code already). Using Visual Studio 2010 Express version 10.0.40219.1 Sp1Rel.

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• How much effort do you have to put in to get gains from using SSE?

  - by John

  Case One Say you have a little class: class Point3D { private: float x,y,z; public: operator+=() ...etc }; Point3D &Point3D::operator+=(Point3D &other) { this->x += other.x; this->y += other.y; this->z += other.z; } A naive use of SSE would simply replace these function bodies with using a few intrinsics. But would we expect this to make much difference? MMX used to involve costly state cahnges IIRC, does SSE or are they just like other instructions? And even if there's no direct "use SSE" overhead, would moving the values into SSE registers and back out again really make it any faster? Case Two Instead, you're working with a less OO-based code base. Rather than an array/vector of Point3D objects, you simply have a big array of floats: float coordinateData[NUM_POINTS*3]; void add(int i,int j) //yes it's unsafe, no overlap check... example only { for (int x=0;x<3;++x) { coordinateData[i*3+x] += coordinateData[j*3+x]; } } What about use of SSE here? Any better? In conclusion Is trying to optimise single vector operations using SSE actually worthwhile, or is it really only valuable when doing bulk operations?

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• Refactoring exercise with generics

  - by Berryl

  I have a variation on a Quantity (Fowler) class that is designed to facilitate conversion between units. The type is declared as: public class QuantityConvertibleUnits<TFactory> where TFactory : ConvertableUnitFactory, new() { ... } In order to do math operations between dissimilar units, I convert the right hand side of the operation to the equivalent Quantity of whatever unit the left hand side is in, and do the math on the amount (which is a double) before creating a new Quantity. Inside the generic Quantity class, I have the following: protected static TQuantity _Add<TQuantity>(TQuantity lhs, TQuantity rhs) where TQuantity : QuantityConvertibleUnits<TFactory>, new() { var toUnit = lhs.ConvertableUnit; var equivalentRhs = _Convert<TQuantity>(rhs.Quantity, toUnit); var newAmount = lhs.Quantity.Amount + equivalentRhs.Quantity.Amount; return _Convert<TQuantity>(new Quantity(newAmount, toUnit.Unit), toUnit); } protected static TQuantity _Subtract<TQuantity>(TQuantity lhs, TQuantity rhs) where TQuantity : QuantityConvertibleUnits<TFactory>, new() { var toUnit = lhs.ConvertableUnit; var equivalentRhs = _Convert<TQuantity>(rhs.Quantity, toUnit); var newAmount = lhs.Quantity.Amount - equivalentRhs.Quantity.Amount; return _Convert<TQuantity>(new Quantity(newAmount, toUnit.Unit), toUnit); } ... same for multiply and also divide I need to get the typing right for a concrete Quantity, so an example of an add op looks like: public static ImperialLengthQuantity operator +(ImperialLengthQuantity lhs, ImperialLengthQuantity rhs) { return _Add(lhs, rhs); } The question is those verbose methods in the Quantity class. The only change between the code is the math operator (+, -, *, etc.) so it seems that there should be a way to refactor them into a common method, but I am just not seeing it. How can I refactor that code? Cheers, Berryl

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• templete class c++

  - by inna karpasas

  hi! i try to design a templete for my universty project. i wrote the follwing cod: #ifndef _LinkedList_H_ #define _LinkedList_H_ #include "Link.h" #include <ostream> template <class L>//error one class LinkedList { private: Link<L> *pm_head; Link<L> * pm_tail; int m_numOfElements; Link<L>* FindLink(L * dataToFind); public: LinkedList(); ~LinkedList(); int GetNumOfElements(){return m_numOfElements;} bool Add( L * data); L *FindData(L * data); template <class L> friend ostream & operator<<(ostream& os,const LinkedList<L> listToprint);//error two L* GetDataOnTop(); bool RemoveFromHead(); L* Remove(L * toRemove); this templete uses the link class templete #ifndef _Link_H_ #define _Link_H_ template <class T>//error 3 class Link { private: T* m_data; Link* m_next; Link* m_prev; public: Link(T* data); ~Link(void); bool Link::operator ==(const Link& other)const; /*getters*/ Link* GetNext()const {return m_next;} Link* GetPrev()const {return m_prev;} T* GetData()const {return m_data;} //setters void SetNext(Link* next) {m_next = next;} void SetPrev(Link* prev) {m_prev = prev;} void SetData(T* data) {m_data = data;} }; error one: shadows template parm class L' error two:declaration ofclass L' error three: shadows template parm `class T' i dont understand what is the problem. i can relly usr your help thank you :)

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• Why do bind1st and bind2nd require constant function objects?

  - by rlbond

  So, I was writing a C++ program which would allow me to take control of the entire world. I was all done writing the final translation unit, but I got an error: error C3848: expression having type 'const `anonymous-namespace'::ElementAccumulator<T,BinaryFunction>' would lose some const-volatile qualifiers in order to call 'void `anonymous-namespace'::ElementAccumulator<T,BinaryFunction>::operator ()(const point::Point &,const int &)' with [ T=SideCounter, BinaryFunction=std::plus<int> ] c:\program files (x86)\microsoft visual studio 9.0\vc\include\functional(324) : while compiling class template member function 'void std::binder2nd<_Fn2>::operator ()(point::Point &) const' with [ _Fn2=`anonymous-namespace'::ElementAccumulator<SideCounter,std::plus<int>> ] c:\users\****\documents\visual studio 2008\projects\TAKE_OVER_THE_WORLD\grid_divider.cpp(361) : see reference to class template instantiation 'std::binder2nd<_Fn2>' being compiled with [ _Fn2=`anonymous-namespace'::ElementAccumulator<SideCounter,std::plus<int>> ] I looked in the specifications of binder2nd and there it was: it took a const AdaptibleBinaryFunction. So, not a big deal, I thought. I just used boost::bind instead, right? Wrong! Now my take-over-the-world program takes too long to compile (bind is used inside a template which is instantiated quite a lot)! At this rate, my nemesis is going to take over the world first! I can't let that happen -- he uses Java! So can someone tell me why this design decision was made? It seems like an odd decision. I guess I'll have to make some of the elements of my class mutable for now...

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