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• C++ difference of keywords 'typename' and 'class' in templates

  - by Mat

  For templates I have seen both declarations: template < typename T > And: template < class T > What's the difference? And what exactly do those keywords mean in the following example (taken from the German Wikipedia article about templates)? template < template < typename, typename > class Container, typename Type > class Example { Container< Type, std::allocator < Type > > baz; };

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• Compilation failing - no #include - boost

  - by jwoolard

  Hi, I'm trying to compile a third-party library, but g++ is complaining about the following line: typedef boost::shared_ptr<MessageConsumer> MessageConsumerPtr; The strange thing is, there is no #include directive in the file - and it is clearly supposed to be this way; there are about 60 files with the same (or very similar) issues. Clearly if there was an #include directive referencing the relevant boost header this would compile cleanly. My question is: how can I get g++ to somehow automagically find the relevant symbol (in all instances of this issue, it is a namespace that can't be found - usually std:: or boost::) by either automatically processing the relevant header (or some other mechanism). Thanks. Edit My current g++ call looks like: g++ -fPIC -O3 -DUSING_PCH -D_REENTRANT -I/usr/include/boost -I./ -c MessageInterpreter.cpp -o MessageInterpreter.o

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• C++ Char without Limit

  - by Lienau

  I'm pretty well versed in C#, but I decided it would be a good idea to learn C++ as well. The only thing I can't figure out is chars. I know you can use the string lib but I also want to figure out chars. I know you can set a char with a limit like this: #include <iostream> using namespace std; int main() { char c[128] = "limited to 128"; cout << c << endl; system("pause"); return 0; } But how would I make a char without a limit? I've seen chars with * but I though that was for pointers. Any help is greatly appreciated.

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• Why does the Win32-API have so many custom types?

  - by sub

  I'm new to the Win32 API and the many new types begin to confuse me. Some functions take 1-2 ints and 3 UINTS as arguments. Why can't they just use ints? What are UINTS? Then, there are those other types: DWORD LPCWSTR LPBOOL Again, I think the "primitive" C types would be enough - why introduce 100 new types? This one was a pain: WCHAR* I had to iterate through it and push_back every character to an std::string as there wasn't another way to convert it to one. Horrible. Why WCHAR? Why reinvent the wheel? They could have just used char* instead, or?

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• How does make_pair know the types of its args?

  - by bobobobo

  The definition for make_pair in the MSVC++ "utility" header is: template<class _Ty1, class _Ty2> inline pair<_Ty1, _Ty2> make_pair(_Ty1 _Val1, _Ty2 _Val2) { // return pair composed from arguments return (pair<_Ty1, _Ty2>(_Val1, _Val2)); } I use make_pair all the time though without putting the argument types in angle brackets: map<string,int> theMap ; theMap.insert( make_pair( "string", 5 ) ) ; Shouldn't I have to tell make_pair that the first argument is std::string and not char* ? How does it know?

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• Misunderstanding function pointer - passing it as an argument

  - by Stef

  I want to pass a member function of class A to class B via a function pointer as argument. Please advise whether this road is leading somewhere and help me fill the pothole. #include <iostream> using namespace std; class A{ public: int dosomeA(int x){ cout<< "doing some A to "<<x <<endl; return(0); } }; class B{ public: B(int (*ptr)(int)){ptr(0);}; }; int main() { A a; int (*APtr)(int)=&A::dosomeA; B b(APtr); return 0; } This brilliant piece of code leaves me with the compiler error: cannot convert int (A::*)(int)' toint (*)(int)' in initialization Firstly I want it to compile. Secondly I don't want dosomeA to be STATIC.

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• Switch/Case statements in C++

  - by vgoklani

  Regarding the switch/case statement in the C++ code below: "Case 1" is obviously false, so how/why does it enter the do-while loop? #include <iostream> using namespace std; int main() { int test = 4; switch(test) { case 1: do { case 2: test++; case 3: test++; case 4: cout << "How did I get inside the do-while loop?" << endl; break; case 5: test++; } while(test > 0); cout << test << endl; } }

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• [C++] which is better, throw an exception or return nonzero value?

  - by xis19

  While you are doing C++ programming, you have two choices of reporting an error. I suppose many teachers would suggest you throw an exception, which is derived from std::exception. Another way, which might be more "C" style, is to return a non-zero value, as zero is "ERROR_SUCCESS". Definitively, return an exception can provide much more information of the error and recovery; while the code will bloat a little bit, and making exception-safe in your mind is a little difficult for me, at least. Other way like returning something else, will make reporting an error much easier; the defect is that managing recovery will be a possibly big problem. So folks, as good programmers, which would be your preference, not considering your boss' opinion? For me, I would like to return some nonzero values.

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• Assign RegEx submatches to variables or map (C++/C)

  - by Michael

  I need to extract the SAME type of information (e.g. First name, Last Name, Telephone, ...), from numerous different text sources (each with a different format & different order of the variables of interest). I want a function that does the extraction based on a regular expression and returns the result as DESCRIPTIVE variables. In other words, instead of returning each match result as submatch[0], submatch[1], submatch[2], ..., have it do EITHER of the following: 1.) return std::map so that the submatches can be accessed via: submatch["first_name"], submatch["last_name"], submatch["telephone"] 2.) return a variables with the submatches so that the submatches can be accessed via: submatch_first_name, submatch_last_name, submatch_telephone I can write a wrapper class around boost::regex to do #1, but I was hoping there would be a built-in or a more elegant way to do this in C++/Boost/STL/C.

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• C# creating a custom user interface

  - by CSharpInquisitor

  Hi, I have a SQL database holding a number of numeric and text values that get updated regularly. The exact number/type/names of these data points can change depending on the source of the database writes. I would like to create a user interface editor, where the user can add database points to the UI and arrange them and format them as they want. If a new point is added to the database they can right click on the UI and say "add this point" and choose from a list of database points. I'm looking for some pointers on where to start on creating this editor application, could something clever be done using XAML to dynamically create std WPF controls at runtime? Thanks in advance for any help, Si

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• C++ vector insights

  - by Sunscreen

  Hi, I am a little bit frustrated of how to use vectors in C++. I use them widely though I am not exactly certail of how I use them. Below are teh questions? If I have a vector lets say: std::vector<CString> v_strMyVector, with (int)v_strMyVector.size > i can I access the i member: v_strMyVector[i] == "xxxx"; ? (it works, though why?) Do i always need to define an iterator to acces to go to the beginning of the vector, and lop on its members ? What is the purpose of an iterator if I have access to all members of the vector directly (see 1)? Thanks in advance, Sun

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• Problem with non-copyable classes

  - by DeadMG

  I've got some non-copyable classes. I don't invoke any of the copy operators or constructor, and this code compiles fine. But then I upgraded to Visual Studio 2010 Ultimate instead of Professional. Now the compiler is calling the copy constructor- even when the move constructor should be invoked. For example, in the following snippet: inline D3D9Mesh CreateSphere(D3D9Render& render, float radius, float slices) { D3D9Mesh retval(render); /* ... */ return std::move(retval); } Error: Cannot create copy constructor, because the class is non-copyable. However, I quite explicitly moved it.

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• templated class : accessing derived normal-class methods

  - by user1019129

  I have something like this : class Container1 { public: method1() { ... } } class Container2 { public: method1() { ... } } template<class C = Container1> class X : public C { public: using C::method1(); ..... X(string& str) : C(str) {}; X& other_method() { method1(); ...; } } My question is why I have to use "using C::method1()", to be able to access the method.. Most of answers I found is for the case where templated-class inhering templated-class. Normally they mention using "this-", but this does not seem to work in this case. Can I do something else shorter... Also I'm suspecting the other error I'm getting is related to the same problem : no match call for (X<Container1>) (<std::string&>)

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• What is wrong with my loop?

  - by user3966541

  I have the following loop and don't understand why it only runs once: std::vector<sf::RectangleShape> shapes; const int res_width = 640; const int res_height = 480; for (int x = 0; x < res_width / 50; x += 50) { for (int y = 0; y < res_height / 50; y += 50) { sf::RectangleShape shape(sf::Vector2f(50, 50)); shape.setPosition(x * 50, y * 50); sf::Color color = (x % 2 == 0) ? sf::Color::Green : sf::Color::Red; shape.setFillColor(sf::Color::Green); shapes.push_back(shape); } }

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• Why does this C++ char array seem to be able to hold more than its size?

  - by Phenom

  #include <iostream> using namespace std; typedef struct { char streetName[5]; } RECORD; int main() { RECORD r; cin >> r.streetName; cout << r.streetName << endl; } When I run this program, if I enter in more than 5 characters, the output will show the whole string I entered. It does not truncate at 5 characters. Why is that? How can I get this to work correctly?

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• creating a custom user interface in WPF

  - by CSharpInquisitor

  I have a SQL database holding a number of numeric and text values that get updated regularly. The exact number/type/names of these data points can change depending on the source of the database writes. I would like to create a user interface editor, where the user can add database points to the UI and arrange them and format them as they want. If a new point is added to the database they can right click on the UI and say "add this point" and choose from a list of database points. I'm looking for some pointers on where to start on creating this editor application, could something clever be done using XAML to dynamically create std WPF controls at runtime?

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• trying to sort a simple string in c++

  - by every_answer_gets_a_point

  #include "stdio.h" #include "conio.h" #include <iostream> using namespace std; int main (void) { char my_char[] = "happy birthday"; int i; bool j=false; char my_char_temp[1]; do { for (i=0;i<sizeof(my_char)-2;i++) { j=false; if (my_char[i+1] < my_char[i]) { my_char_temp[0]=my_char[i+1]; my_char[i+1] = my_char[i]; my_char[i] = my_char_temp[0]; j=true; } } }while (j); cout << my_char; } what am i doing wrong? im just trying to sort the letters within the char the output i get is completely wrong

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• How to find out how namespace got polluted?

  - by dehmann

  Consider the following little piece of code: // all of these include other headers, lots of code: #include "myheader1.h" #include "myheader2.h" #include <string> void foo() { string s("hello world"); // oh no, why does this compile?? } This compiles, so obviously some of the recursively included header files has a using namespace std; somewhere. How would you go about finding out where that offending line of code is? Just using grep on all header files won't really work because that statement is often used inside a function, where it is safe and won't pollute the rest of the code.

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• C++ setting up "flags"

  - by sub

  Example: enum Flags { A, B, C, D }; class MyClass { std::string data; int foo; // Flags theFlags; (???) } How can I achieve that it is possible to set any number of the "flags" A,B,C and D in the enum above in an instance of MyClass? My goal would be something like this: if ( MyClassInst.IsFlagSet( A ) ) // ... MyClassInst.SetFlag( A ); //... Do I have to use some array or vector? If yes, how? Are enums a good idea in this case?

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• Force type of C++ template

  - by gregseth

  Hi, I've a basic template class, but I'd like to restrain the type of the specialisation to a set of classes or types. e.g.: template <typename T> class MyClass { .../... private: T* _p; }; MyClass<std::string> a; // OK MYCLass<short> b; // OK MyClass<double> c; // not OK Those are just examples, the allowed types may vary. Is that even possible? If it is, how to do so? Thanks.

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• Did anybody use the constream (constrea.h) lib?

  - by user337938

  Two years ago, I used the conio.h (actually conio2.h for Dev-C++) to create a console form interface. Now I want to make the same thing, but C++ std lib does not provide the needed functions and I don't want to use the old C conio lib. I found some websites which highlights the constream lib, but I have no idea to use it on VS! I tried just copying the header file into my project, but VS show several erros. I believe I am doing something wrong. ps: i got this file: ftp://ftp.cs.technion.ac.il/pub/misc/baram/TC31/INCLUDE/CONSTREA.H

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• Can typeid() be used to pass a function?

  - by Kerb_z

  I tried this and got the output as: void Please explain the following Code: #include <cstdio> #include <typeinfo> using namespace std ; void foo() { } int main(void) { printf("%s", typeid(foo()).name());// Please notice this line, is it same as typeid( ).name() ? return 0; } AFAIK: The typeid operator allows the type of an object to be determined at run time. So, does this sample code tell us that a function that returns void is of *type void*. I mean a function is a method and has no type. Correct?

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• C++ template + typedef

  - by MMS

  What is wrong in the following code: Point2D.h template <class T> class Point2D { private: T x; T y; ... }; PointsList.h template <class T> class Point2D; template <class T> struct TPointsList { typedef std::vector <Point2D <T> > Type; }; template <class T> class PointsList { private: TPointsList <T>::Type points; //Compiler error ... }; I would like to create new user type TPointsList without direct type specification...

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• Weird output as the numbers get bigger in Fibonacci sequence

  - by Jon

  I noticed in my fibonacci sequence that I'm getting negative numbers after a certain point. Does this have to do with the limited range of "int"? or is there something wrong with my code? Here is the code: using std::cout; int main() { int n = 50, f1 = 0, f2 = 1, fn = 0, i = 0; cout << "0 "; for (i = 0; i < n; i++) { fn = f1 + f2; f2 = f1; f1 = fn; cout << fn << " "; }

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• How to compare string with const char*?

  - by arzeth

  #include <stdlib.h> #include <stdio.h> #include <iostream> #include <string.h> using namespace std; int main() { string cmd; while(strcmp(cmd.c_str(),"exit")==0 && strcmp(cmd.c_str(),"\exit")==0) { cin>>cmd; cout<<cmd; } return 0; } I am stuck.

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