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• Delphi 2010 - Why can't I declare an abstract method with a generic type parameter?

  - by James

  I am trying to do the following in Delphi 2010: TDataConverter = class abstract public function Convert<T>(const AData: T): string; virtual; abstract; end; However, I keep getting the following compiler error: E2533 Virtual, dynamic and message methods cannot have type parameters I don't quite understand the reason why I can't do this. I can do this in C# e.g. public abstract class DataConverter { public abstract string Convert<T>(T data); } Anyone know the reasoning behind this?

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• Solving C++ 'target of assignment not really an lvalue' errors

  - by Jason

  Given this code: void FrMemCopy(void *to, const void *from, size_t sz) { size_t sz8 = sz >> 3; size_t sz1 = sz - (sz8 << 3); while (sz8-- != 0) { *((double *)to)++ = *((double *)from)++; } while (sz1-- != 0) { *((char *)to)++ = *((char *)from)++; } } I am receiving target of assignment not really an lvalue warnings on the 2 lines inside the while loops. Can anyone break down those lines? a cast then an increment? What is a simplier way to write that? What does the error mean?

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• Does a c/c++ compiler optimize constant divisions by power-of-two value into shifts?

  - by porgarmingduod

  Question says it all. Does anyone know if the following... size_t div(size_t value) { const size_t x = 64; return value / x; } ...is optimized into? size_t div(size_t value) { return value >> 6; } Do compilers do this? (My interest lies in GCC). Are there situations where it does and others where it doesn't? I would really like to know, because every time I write a division that could be optimized like this I spend some mental energy wondering about whether precious nothings of a second is wasted doing a division where a shift would suffice.

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• Large amount of constants in Java

  - by Lars D

  I need to include about 1 MByte of data in a Java application, for very fast and easy access in the rest of the source code. My main background is not Java, so my initial idea was to convert the data directly to Java source code, defining 1MByte of constant arrays, classes (instead of C++ struct) etc., something like this: public final/immutable/const MyClass MyList[] = { { 23012, 22, "Hamburger"} , { 28375, 123, "Kieler"} }; However, it seems that Java does not support such constructs. Is this correct? If yes, what is the best solution to this problem?

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• How do I simplify this templated vector initializer loop using lambdas or STL transform?

  - by Neil G

  How do I simplify this templated vector initializer loop using lambdas or some kind of STL transform? template<typename T> template<typename... Args> void InitToRandomValues(vector<T>* retval, int n, RNG& rng, Args const&... args) { retval->resize(n); for (auto it = retval->begin(); it != retval->end(); ++it) { typename T::CPDDist cpd(rng, args...); *it = T(cpd); } }

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• How to insert into std::map.

  - by Knowing me knowing you

  In code below: map<string,vector<int>> create(ifstream& in, const vector<string>& vec) { /*holds string and line numbers into which each string appears*/ typedef map<string,vector<int>> myMap; typedef vector<string>::const_iterator const_iter; myMap result; string tmp; unsigned int lineCounter = 0; while(std::getline(in,tmp)) { const_iter beg = vec.begin(); const_iter end = vec.end(); while (beg < end) { if ( tmp.find(*beg) != string::npos) { result[*beg].push_back(lineCounter);//THIS IS THE LINE I'M ASKING FOR } ++beg; } ++lineCounter; } return result; } How should I do it (check line commented in code) if I want to use insert method of map instead of using operator[]? Thank you.

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• Where should we manage session objects in an ASP.NET application?

  - by Kumar

  I am developing a 3-tired ASP.NET C# web application and was wondering where should the sessions be managed. I have a SessionManager class as follows: public sealed class SessionManager { private const string USER = "User"; private SessionManager() { } public static SessionManager Instance { get { return _instance; } } public User User { get { return HttpContext.Current.Session[USER] as User; } set { HttpContext.Current.Session[USER] = value; } } } Now should the session information be managed in the Business Logic Layer or should it be managed in the Presentation Layer?

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• .NET's double.NaN - how does this counterintuitive feature work?

  - by GeReV

  I stumbled upon the definition of double.NaN in code: public const double NaN = (double)0.0 / (double)0.0; This is done similarly in PositiveInfinity and NegativeInfinity. double.IsNaN (with removing a few #pragmas and comments) is defined as: [Pure] [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)] public static bool IsNaN(double d) { if (d != d) { return true; } else { return false; } } This is, by far, the most counterintuitive thing I have ever seen in the .NET framework. How is 0.0 / 0.0 represented "behind the scenes"? How can division by 0 be possible in double, and why does NaN != NaN?

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• Printing escape character

  - by danutenshu

  When I am given "d""\"/""b", I need to print out the statement character for character. (d, b, a slash, a backslash, and 5 quotes) in C++. The only errors that show now are the lines if(i.at(j)="\\") and else if(i.at(j)="\""). Also, how should the outside double apostrophes be excluded? #include <iostream> #include <cstdlib> using namespace std; int main (int argc, const char* argv[] ) { string i= argv[1]; for (int j=0; j>=sizeof(i)-1; j++) { if(i.at(j)="\\") { cout << "\\"; } else if(i.at(j)="\"") { cout << "\""; } else { cout << i.at(j); } } return 0; }

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• How to retrieve all keys (or values) from a std::map?

  - by Owen

  This is one of the possible ways I come out: struct RetrieveKey { template <typename T> typename T::first_type operator()(T keyValuePair) const { return keyValuePair.first; } }; map<int, int> m; vector<int> keys; // Retrieve all keys transform(m.begin(), m.end(), back_inserter(keys), RetrieveKey()); // Dump all keys copy(keys.begin(), keys.end(), ostream_iterator<int>(cout, "\n")); Of course, we can also retrieve all values from the map by defining another functor RetrieveValues. Is there any other way to achieve this easily? (I'm always wondering why std::map does not include a member function for us to do so.)

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• Issues with dynamically allocating a string array

  - by Jason Block

  Brand new to C. I am trying to dynamically allocate the array frags2 of size numberOfFrags and copy over the contents of the original array to it. I have tried numerous approaches and searching and do not understand what is going wrong here. Sizeof on the new array returns 0 instead of what I thought I malloc'd. Any help would be much appreciated! int main(int argc, const char* argv[]) { char* frags[MAX_FRAG_COUNT]; FILE* fp = fopen(argv[1], "r"); int numberOfFrags = ReadAllFragments(fp, frags, MAX_FRAG_COUNT); fclose(fp); char** frags2 = (char**)malloc(numberOfFrags * sizeof(char*)); for (int i = 0; i < numberOfFrags; i++) { frags2[i] = frags[i]; } qsort(frags2, sizeof(frags2) / sizeof(char *), sizeof(char*), cstring_cmp);

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• Running for loop depending on size of string vector

  - by xbonez

  I have made a string vector vector actor_; and then added elements in it using push_back. I now want to display all of them, for which I need to run a loop according to the number of elements in the vector. For that, I need to run the following loop: for (int i = 0; i < (int)actor_.size; i++) { } but this returns the following error: error C2440: 'type cast' : cannot convert from 'unsigned int (__thiscall std::vector<_Ty::* )(void) const' to 'int' 1 with 1 [ 1 _Ty=std::string 1 ] 1 There is no context in which this conversion is possible

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• How can I declare constant strings for use in both an unmanaged C++ dll and in a C# application?

  - by Surfbutler

  Curently I'm passing my const string values up from my C++ into my C# at startup via a callback, but I'm wondering if there's a way of defining them in a C++ header file that I can then also refer to in C#. I already do this with enums as they are easy. I include a file in both my C++ library project (via a .h file with a pragma once at the top), and my C# application (as a link): #if _NET public #endif enum ETestData { First, Second }; I know it sounds messy, but it works :) But...how can I do the same with string constants - I'm initially thinking the syntax is too different between the platforms, but maybe there's a way? Using clever syntax involving #if _NET, #defines etc? Using resource files? Using a C++/CLI library? Any ideas?

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• Question about r-value in C++0x

  - by Goofy

  Rvalues IMHO are great improvement in C++, but at the beginning the're seems quite. Please look at code below: #include <string> std::string && foo (void) { std::string message ("Hello!"); return std::move (message); } void bar (const std::string &message2) { if (message == "Bye Bye!") return; } int main () { bar (foo ()); } Reference message2 is last owner of original message object returned by foo(), right?

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• Programmatically check whether a linux kernel module exists or not at runtime

  - by dgraziotin

  I am writing a C daemon, which depends on the existence of two kernel modules in order to do its job. The program does not directly use these (or any other) modules. It only needs them to exist. Therefore, I would like to programmatically check whether these modules are already loaded or not, in order to warn the user at runtime. Before I start to do things like parsing /proc/modules or lsmod output, does a utility function already exist somewhere? Something like is_module_loaded(const char* name); I am pretty sure this has been asked before. However, I think I am missing the correct terms to search for this. Thanks!

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• .net equivalent for php preg_replace

  - by Hath

  What is the c#.net equivalent for php's preg_replace function? php code is like this: const ALLOW_VALUES = '[^a-z0-9àáâäèéêëìíîïòóôöùûwýÿyÁÂÄÈÉÊËÌÎÏÒÓÔÖÙÛÜWYÝ]'; public function streetTownHash($data, $hashCheck = false, $updateRecord = false) { foreach($data as $key=>$value){ try{ $value = mb_convert_case($value, MB_CASE_LOWER, "UTF-8"); } catch(Exception $e) { echo "Requires extension=php_mbstring.dll enabled ! - $e"; } $valueConcat .= preg_replace('/'.self::ALLOW_VALUES.'/','',$value); # Remove punctuation etc } $streetTownHash = sha1($valueConcat); .... this is as far as i've got but not sure about it.. private SHA1 hash = SHA1.Create(); private string hashAllowed = "[^a-z0-9àáâäèéêëìíîïòóôöùûwýÿyÁÂÄÈÉÊËÌÎÏÒÓÔÖÙÛÜWYÝ]"; public string HashString(string value) { value = // = regex not sure this part var bytes = ASCIIEncoding.UTF8.GetBytes(value); var hashed = hash.ComputeHash(bytes); return ASCIIEncoding.UTF8.GetString(hashed); }

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• lambda+for_each+delete on STL containers

  - by rubenvb

  I'm trying to get a simple delete every pointer in my vector/list/... function written with an ultra cool lambda function. Mind you, I don't know c**p about those things :) template <typename T> void delete_clear(T const& cont) { for_each(T.begin(), T.end(), [](???){ ???->delete() } ); T.clear(); } I have no clue what to fill in for the ???'s. Any help is greatly appreciated!

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• delegating into private parts

  - by FredOverflow

  Sometimes, C++'s notion of privacy just baffles me :-) class Foo { struct Bar; Bar* p; public: Bar* operator->() const { return p; } }; struct Foo::Bar { void baz() { std::cout << "inside baz\n"; } }; int main() { Foo::Bar b; // error: 'struct Foo::Bar' is private within this context Foo f; f->baz(); // fine } Since Foo::Bar is private, I cannot declare b in main. Yet I can call methods from Foo::Bar just fine. Why the hell is this allowed? Was that an accident or by design?

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• Can't subtract in a for loop in C/Objective-C

  - by user1612935

  I'm going through the Big Nerd Ranch book on Objective-C, which takes you through some early C stuff. I've played with C before, and am pretty experienced in PHP. Anyhow, I'm doing the challenges and this one is not working the way I think it should. It's pretty simple - start at 99, loop through and subtract three until you get to zero, and every time you get a number that is divisible by 5 print "Found one." Pretty straightforward. However, subtracting by three in the for loop is not working #include <stdio.h> int main (int argc, const char * argv[]) { int i; for(i = 99; i > 0; i-3){ printf("%d\n", i); if(i % 5 == 0) { printf("Found one!\n"); } } return 0; } It creates and endless loop at 99, and I'm not sure why.

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• How to call a function from a shared library?

  - by Frank

  What is the easiest and safest way to call a function from a shared library / dll? I am mostly interested in doing this on linux, but it would be better if there were a platform-independent way. Could someone provide example code to show how to make the following work, where the user has compiled his own version of foo into a shared library? // function prototype, implementation loaded at runtime: std::string foo(const std::string); int main(int argc, char** argv) { LoadLibrary(argv[1]); // loads library implementing foo std::cout << "Result: " << foo("test"); return 0; } BTW, I know how to compile the shared lib (foo.so), I just need to know an easy way to load it at runtime.

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• Strange type in c++

  - by Cemre

  I have a method with the prototype: bool getAssignment(const Query& query, Assignment *&result); I am a bit confused about the type of the second param (Assignment *&result) since I don't think I have seen something like that before. It is used like: Assignment *a; if (!getAssignment(query, a)) return false; Is it a reference to a pointer or the other way around ? or neither ? Any explanation is appreciated. Thanks.

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• Obtain container type from (its) iterator type in C++ (STL)

  - by KRao

  It is easy given a container to get the associated iterators, example: std::vector<double>::iterator i; //An iterator to a std::vector<double> I was wondering if it is possible, given an iterator type, to deduce the type of the "corresponding container" (here I am assuming that for each container there is one and only one (non-const) iterator). More precisely, I would like a template metafunction that works with all STL containers (without having to specialize it manually for each single container) such that, for example: ContainerOf< std::vector<double>::iterator >::type evaluates to std::vector<double> Is it possible? If not, why? Thank you in advance for any help!

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• C++ STL: Trouble with string iterators

  - by Rosarch

  I'm making a simple command line Hangman game. void Hangman::printStatus() { cout << "Lives remaining: " << livesRemaining << endl; cout << getFormattedAnswer() << endl; } string Hangman::getFormattedAnswer() { return getFormattedAnswerFrom(correctAnswer.begin(), correctAnswer.end()); } string Hangman::getFormattedAnswerFrom(string::const_iterator begin, string::const_iterator end) { return begin == end? "" : displayChar(*begin) + getFormattedAnswerFrom(++begin, end); } char Hangman::displayChar(const char c) { return c; } (Eventually, I'll change this so displayChar() displays a - or a character if the user has guessed it, but for simplicity now I'm just returning everything.) When I build and run this from VS 2010, I get a popup box: Debug Assertion Failed! xstring Line: 78 Expression: string iterator not dereferenceable What am I doing wrong?

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• c++ compilation error

  - by clamp

  hello, i got a compile error which i do not understand. i have a h/cpp file combination that does not contain a class but just defines some utility functions. when i try to use a struct that is defined in another class i get the error: error C2027: use of undefined type so, stripped down to the problem, the h file looks like this namespace A { void foo(B::C::SStruct const & Var); } the definition of SStruct is in a class which is in another h-file, that is of course included. namespace B { Class C { struct SStruct { }; } } what am i missing here? thanks!

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• [C++] Simple inheritance question

  - by xbonez

  I was going over some sample questions for an upcoming test, and this question is totally confusing me. Any help would be appreciated. Consider the following code: class GraduateStudent : public Student { ... }; If the word "public" is omitted, GraduateStudent uses private inheritance, which means which of the following? GraduateStudent objects may not use methods of Student. GraduateStudent does not have access to private objects of Student. No method of GraduateStudent may call a method of Student. Only const methods of GraduateStudent can call methods of Student.

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