Strange error with iterators

I've wrote this function which should add a comma for every 3 digits in a number (so that it looks something like 5,000). This is my function: std::string formatNumber(int number) { // Convert the int to a string. std::string ...

Posted On: Sunday 25th of November 2012 11:30:52 PM Total Views:  586
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#include #include #include using namespace std; class MyObj { public: int data; ifstream in; }; typedef std::vector MyObjVector; int main(int arc, char* argv[]) { MyObjVector myVector; MyObj obj; = 10;"test.txt"); myVector.push_back(obj); } In the code above, I want to use a vector of class MyObj, which have a ifstream object, but I got a message says that I can't access the private memeber of ios_base, both in MinGW and Visual C++, but if a commented the line myVector.push_back(obj); all thing is OK, can't any one help me! -- [ See for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
strange grammar about volatile and operator overload   (358 Views)
, The following code, Code: operator const Outer::Inner * volatile & (); 1. I think it means an operator &, which returns const Inner* type and takes no arguments, right 2. Adding volatile to return value means (I previously only used volatile to qualify variable) thanks in advance, George , On Jan 29, 10:47 pm, Jack Klein wrote: > On Tue, 29 Jan 2008 14:13:07 +0100, Hans Mull > wrote in comp.lang.c++: > > George2 schrieb: > > > The following code, > > > Code: > > > operator const Outer::Inner * volatile & (); > > > > > > 1. > > > I think it means an operator &, which returns const Inner* > > > type and takes no arguments, right That would be: const Outer::Inner * volatile operator & (); The above is an implicit conversion operator, converting the class in which it is defined to a Outer::Inter const* volatile&. > > > 2. > > > Adding volatile to return value means A top level volatile on a return value is ignored unless the type is a class type. Here 1) the type isn't a class type, but a reference, and 2) the volatile isn't top level, i.e. it isn't on the return type. What the volatile means here is that you limit enormously what the user can do with the pointer referred to. (As Alf pointed out, this is probably a case of exploiting the type system---what's important here isn't the semantics of volatile, but the fact that T* volatile isn't the same type as T* volatile.) > > > (I previously only used volatile to qualify variable) > > volaitle disables optimization > What a silly, incomplete, and absolutely wrong statement! It's incomplete, but that's all. Formally, except for a few special cases (e.g. with longjmp/setjmp), the semantics of volatile are implementation defined. Practically, however, most implementations define them as inhibiting some optimizations. > Consider this code: > extern volatile unsigned int vui; // defined and initialized elsewhere > unsigned int silly_func() > { > return vui * 2; > } > Are you really claiming that the compiler is forbidden from > making the strength reduction optimization of replacing the > multiply with a left shift by 1 No, but if the compiler inlines this function, and happens to find that it has vui in a register, as a result of a previous calculation, it will still reread it. (Or more correctly, it will still generate a machine instruction to load it from memory. On most modern hardware, this does not necessarily mean that it will actually reread it from global memory. In sum, the implementation defined semantics of volatile are, in most cases, totally useless for anything.) -- James Kanze (GABI Software) Conseils en informatique oriente objet/ Beratung in objektorientierter Datenverarbeitung 9 place Smard, 78210 St.-Cyr-l'cole, France, +33 (0)1 30 23 00 34
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Zheng Da wrote: > I want a use the class of map in a class with template, > and the type of elements in map is specified by the parameter of the > class's template. > For example, > template > class hashmap > { > map table; > public: > void find(const key &k){ > map::iterator it=table.find(k); } > }; > > int main() > { > hashmap hm; > } > > When I compile it, I get the error > error: expected `;' before 'it' > I don't get it. Why I can use map in this class, but I can't define > its iterator Read up on 'typename' keyword and where it's supposed to be used. (Hint: there are FAQ entires that have it and there is more than one use of that keyword) V -- Please remove capital 'A's when replying by e-mail I do not respond to top-posted replies, please don't ask
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