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  • std::basic_string full specialization (g++ conflict)

    - by SoapBox
    I am trying to define a full specialization of std::basic_string< char, char_traits<char>, allocator<char> > which is typedef'd (in g++) by the <string> header. The problem is, if I include <string> first, g++ sees the typedef as an instantiation of basic_string and gives me errors. If I do my specialization first then I have no issues. I should be able to define my specialization after <string> is included. What do I have to do to be able to do that? My Code: #include <bits/localefwd.h> //#include <string> // <- uncommenting this line causes compilation to fail namespace std { template<> class basic_string< char, char_traits<char>, allocator<char> > { public: int blah() { return 42; } size_t size() { return 0; } const char *c_str() { return ""; } void reserve(int) {} void clear() {} }; } #include <string> #include <iostream> int main() { std::cout << std::string().blah() << std::endl; } The above code works fine. But, if I uncomment the first #include <string> line, I get the following compiler errors: blah.cpp:7: error: specialization of ‘std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ after instantiation blah.cpp:7: error: redefinition of ‘class std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ /usr/include/c++/4.4/bits/stringfwd.h:52: error: previous definition of ‘class std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ blah.cpp: In function ‘int main()’: blah.cpp:22: error: ‘class std::string’ has no member named ‘blah’ Line 52 of /usr/include/c++/4.4/bits/stringfwd.h: template<typename _CharT, typename _Traits = char_traits<_CharT>, typename _Alloc = allocator<_CharT> > class basic_string; As far as I know this is just a forward delcaration of the template, NOT an instantiation as g++ claims. Line 56 of /usr/include/c++/4.4/bits/stringfwd.h: typedef basic_string<char> string; As far as I know this is just a typedef, NOT an instantiation either. So why are these lines conflicting with my code? What can I do to fix this other than ensuring that my code is always included before <string>?

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  • Why are there two implementations of std::sort (with and without a comparator) rather than one implementation with a default template parameter?

    - by PolyVox
    In my code I'm adopting a design strategy which is similar to some standard library algorithms in that the exact behavior can be customized by a function object. The simplest example is std::sort, where a function object can control how the comparison is made between objects. I notice that the Visual C++ provides two implementations of std::sort, which naturally involves code duplication. I would have imagined that it was instead possible to have only one implementation, and provide a default comparator (using operator< ) as a default template parameter. What is the rational behind two separate versions? Would my suggestion make the interface more complex in some way? Or result in confusing error messages when the object does not provide operator Thanks, David

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  • accessing nth element (value) of a vector after sorting

    - by memC
    dear experts, This question is an extension of this question I asked. I have a std::vector vec_B.which stores instances of class Foo. The order of elements in this vector changes in the code. Now, I want to access the value of the current "last element" or current 'nth' element of the vector. If I use the code below to get the last element using getLastFoo() method, it doesn't return the correct value. For example, to begin with the last element of the vector has Foo.getNumber() = 9. After sorting it in descending order of num, for the last element, Foo.getNumber() = 0. But with the code below, it still returns 9.. that means it is still pointing to the original element that was the last element. What change should I make to the code below so that "lastFoo" points to the correct last element? class Foo { public: Foo(int i); ~Foo(){}; int getNum(); private: int num; }; Foo:Foo(int i){ num = i; } int Foo::getNum(){ return num; } class B { public: Foo* getLastFoo(); B(); ~B(){}; private: vector<Foo> vec_B; }; B::B(){ int i; for (i = 0; i< 10; i++){ vec_B.push_back(Foo(i)); } // Do some random changes to the vector vec_B so that elements are reordered. For // example rearrange elements in decreasing order of 'num' //... } Foo* B::getLastFoo(){ &vec_B.back(); }; int main(){ B b; Foo* lastFoo; lastFoo = b.getLastFoo() cout<<lastFoo->getNumber(); return 0; }

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  • Does operator precedence in C++ differ for pointers and iterators?

    - by oraz
    The code below demonstrates this difference: #include <iostream> #include <string> int main() { char s[] = "ABCD"; std::string str(s); char *p = s; while(*p) { *p++ = tolower(*p); // <-- incr after assignment } std::cout << s << std::endl; std::string::iterator it = str.begin(), end = str.end(); while(it != end) { *it++ = tolower(*it); // <-- incr before assignment ? } std::cout << str << std::endl; return 0; } the code above outputs: abcd bcd if we separate assignment operation and increment operator: while(it != end) { *it = tolower(*it); // <-- incr before assignment ? it++; } the output will be as expected. What's wrong with the original code? $ g++ --version g++ (GCC) 3.4.4 (cygming special, gdc 0.12, using dmd 0.125) Copyright (C) 2004 Free Software Foundation, Inc.

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  • C++ std::vector memory/allocation

    - by aaa
    from a previous question about vector capacity, http://stackoverflow.com/questions/2663170/stdvector-capacity-after-copying, Mr. Bailey said: In current C++ you are guaranteed that no reallocation occurs after a call to reserve until an insertion would take the size beyond the value of the previous call to reserve. Before a call to reserve, or after a call to reserve when the size is between the value of the previous call to reserve and the capacity the implementation is allowed to reallocate early if it so chooses. So, if I understand correctly, in order to assure that no relocation happens until capacity is exceeded, I must do reserve twice? can you please clarify it? I am using vector as a memory stack like this: std::vector<double> memory; memory.reserve(size); memory.insert(memory.end(), matrix.data().begin(), matrix.data().end()); // smaller than size size_t offset = memory.size(); memory.resize(memory.capacity(), 0); I need to guarantee that relocation does not happen in the above. thank you. ps: I would also like to know if there is a better way to manage memory stack in similar manner other than vector

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  • Is the "==" operator required to be defined to use std::find

    - by user144182
    Let's say I have: class myClass std::list<myClass> myList where myClass does not define the == operator and only consists of public fields. In both VS2010 and VS2005 the following does not compile: myClass myClassVal = myList.front(); std::find( myList.begin(), myList.end(), myClassVal ) complaining about lack of == operator. I naively assumed it would do a value comparison of the myClass object's public members, but I am almost positive this is not correct. I assume if I define a == operator or perhaps use a functor instead, it will solve the problem. Alternatively, if my list was holding pointers instead of values, the comparison would work. Is this right or should I be doing something else?

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  • Checkbox Issue with IE8 using jquery

    - by rockers
    I have this code $('#Submit').click(function(event) { var checked = $('.inputchbox'); ......IE8 var ids= checked.map(function() { return $(this).val(); }).get().join(','); alert(ids); }); This Code return all the values which is there for Checkboxbox (.inputchbox is class for the checkbox) but If I give somethign like this var checked = $('.inputchbox input:checkbox:checked'); or var checked = $('.inputchbox input[type=checkbox]:checked'); or var checked = $('.inputchbox input[name=chk]:checked'); or var checked = $('.inputchbox').find('input[type=checkbox]:checked'); if i am giving like this nothing is working for me I am not getting the result in IE8? var checked = $('.inputchbox'); .....this is working but I am getting the checkboxes ids its doesnot checking wheather its checked or not.. I need to get only checked chekcbox id's thanks

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  • which is better in general, map or vector in c++?

    - by tsubasa
    As I know that accessing an element in vector takes constant time while in map takes logarithmic time. However, storing a map takes less memory than storing a vector. Therefore, I want to ask which one is better in general? I'm considering using one of those two in my program, which has about 1000 elements. I plan to use 3 dimensional vector, which would take 1000x1000x1000 elements.

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  • How to negate a predicate function using operator ! in C++?

    - by Chan
    Hi, I want to erase all the elements that do not satisfy a criterion. For example: delete all the characters in a string that are not digit. My solution using boost::is_digit worked well. struct my_is_digit { bool operator()( char c ) const { return c >= '0' && c <= '9'; } }; int main() { string s( "1a2b3c4d" ); s.erase( remove_if( s.begin(), s.end(), !boost::is_digit() ), s.end() ); s.erase( remove_if( s.begin(), s.end(), !my_is_digit() ), s.end() ); cout << s << endl; return 0; } Then I tried my own version, the compiler complained :( error C2675: unary '!' : 'my_is_digit' does not define this operator or a conversion to a type acceptable to the predefined operator I could use not1() adapter, however I still think the operator ! is more meaningful in my current context. How could I implement such a ! like boost::is_digit() ? Any idea? Thanks, Chan Nguyen

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  • C++ std::vector capacity

    - by aaa
    hi. does vector::operator= change vector capacity? if so, how? does copy constructor copy capacity? I looked through documentation but could not find specific answer. is it implementation dependent? Thanks

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  • How to call operator<< on "this" in a descendant of std::stringstream?

    - by romkyns
    class mystream : public std::stringstream { public: void write_something() { this << "something"; } }; This results in the following two compile errors on VC++10: error C2297: '<<' : illegal, right operand has type 'const char [10]' error C2296: '<<' : illegal, left operand has type 'mystream *const ' Judging from the second one, this is because what this points at can't be changed, but the << operator does (or at least is declared as if it does). Correct? Is there some other way I can still use the << and >> operators on this?

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  • C++ Generic List Assignment

    - by S73417H
    I've clearly been stuck in Java land for too long... Is it possible to do the C++ equivalent of the following Java code: // Method List<Bar> getBars() { return new LinkedList<Bar>(); } // Assignment statement. List<Foo> stuff = getBars(); Where Foo is a sub-class of Bar. So in C++.... std::list<Bar> & getBars() { std::list<Bar> bars; return bars; } std::list<Foo> stuff = getBars(); Hope that makes sense....

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  • Insert an element to std::set using constructor

    - by Dave17
    is it possible to insert a new element to std::set like in case of std::list for example: //insert one element named "string" to sublist of mylist std::list< std::list<string> > mylist; mylist.push_back(std::list<string>(1, "string")); Now, mylist has one element of type std::string in its sub-list of type std::list. How can you do the same in if std::set is the sub-set of std::list my list i.e std::list<std::set <string>> mylist; if you can't then why not?

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  • resort on a std::vector vs std::insert

    - by Abruzzo Forte e Gentile
    I have a sorted std::vector of relative small size ( from 5 to 20 elements ). I used std::vector since the data is continuous so I have speed because of cache. On a specific point I need to remove an element from this vector. I have now a doubt: which is the fastest way to remove this value between the 2 options below? setting that element to 0 and call sort to reorder: this has complexity but elements are on the same cache line. call erase that will copy ( or memcpy who knows?? ) all elements after it of 1 place ( I need to investigate the behind scense of erase ). Do you know which one is faster? I think that the same approach could be thought about inserting a new element without hitting the max capacity of the vector. Regards AFG

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  • What is a truly empty std::vector in C++?

    - by RyanG
    I've got a two vectors in class A that contain other class objects B and C. I know exactly how many elements these vectors are supposed to hold at maximum. In the initializer list of class A's constructor, I initialize these vectors to their max sizes (constants). If I understand this correctly, I now have a vector of objects of class B that have been initialized using their default constructor. Right? When I wrote this code, I thought this was the only way to deal with things. However, I've since learned about std::vector.reserve() and I'd like to achieve something different. I'd like to allocate memory for these vectors to grow as large as possible because adding to them is controlled by user-input, so I don't want frequent resizings. However, I iterate through this vector many, many times per second and I only currently work on objects I've flagged as "active". To have to check a boolean member of class B/C on ever iteration is silly. I don't want these objects to even BE there for my iterators to see when I run through this list. Is reserving the max space ahead of time and using push_back to add a new object to the vector a solution to this?

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  • Nested for_each with lambda not possible?

    - by Ela782
    The following code does not compile in VS2012, it gives error C2064: term does not evaluate to a function taking 1 arguments on the line of the second for_each (line 4 below). vector<string> v1; for_each(begin(v1), end(v1), [](string s1) { vector<string> v2; for_each(begin(v2), end(v2), [](string s2) { cout << "..."; }); }); I found some related stuff like http://connect.microsoft.com/VisualStudio/feedback/details/560907/capturing-variables-in-nested-lambdas which shows a bug (they are doing something different) but on the other hand that shows that what I print above should be possible. What's wrong with the above code?

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  • algorithms that destruct and copy_construct

    - by FredOverflow
    I am currently building my own toy vector for fun, and I was wondering if there is something like the following in the current or next standard or in Boost? template<class T> void destruct(T* begin, T* end) { while (begin != end) { begin -> ~T(); ++begin; } } template<class T> T* copy_construct(T* begin, T* end, T* dst) { while (begin != end) { new(dst) T(*begin); ++begin; ++dst; } return dst; }

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  • need help with C++ using maps to keep track of words in a INPUT file

    - by eNetik
    Let say i have a text file with today is today but tomorrow is today tomorrow then using maps how can i keep track of the words that are repeated? and on which line it repeats? so far i have each string in the file read in as a temp and it is stored in the following way: map<string,int> storage; int count = 1 // for the first line of the file if(infile.is_open()){ while( !infile.eof() ){ getline(in, line); istringstream my_string(line); while(my_string.good()){ string temp; my_string >> temp; storage[temp] = count } count++;// so that every string read in the next line will be recorded as that line. } } map<string,int>::iterator m; for(int m = storage.begin(); m!= storage.end(); m++){ out<<m->first<<": "<<"line "<<m->second<<endl; } right now the output is just but: line 1 is: line 2 today: line 2 tomorrow: line 2 But instead.. it should print out(no repeating strings): today : line 1 occurred 2 times, line 2 occurred 1 time. is: line 1 occurred 1 time, line 2 occurred 1 time. but: line 1 occurred 1 time. tomorrow: line 2 occurred 2 times. Note: the order of the string does not matter. Any help would be appreciated. Thanks.

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  • Vector Troubles in C++

    - by DistortedLojik
    I am currently working on a project that deals with a vector of objects of a People class. The program compiles and runs just fine, but when I use the debugger it dies when trying to do anything with the PersonWrangler object. I currently have 3 different classes, one for the person, a personwrangler which handles all of the people collectively, and a game class that handles the game input and output. Edit: My basic question is to understand why it is dying when it calls outputPeople. Also I would like to understand why my program works exactly as it should unless I use the debugger. The outputPeople function works the way I intended that way. Edit 2: The callstack has 3 bad calls which are: std::vector ::begin(this=0xbaadf00d) std::vector ::size(this=0xbaadf00d) PersonWrangler::outputPeople(this=0xbaadf00d) Relevant code: class Game { public: Game(); void gameLoop(); void menu(); void setStatus(bool inputStatus); bool getStatus(); PersonWrangler* hal; private: bool status; }; which calls outputPeople where it promptly dies from a baadf00d error. void Game::menu() { hal->outputPeople(); } where hal is an object of PersonWrangler type class PersonWrangler { public: PersonWrangler(int inputStartingNum); void outputPeople(); vector<Person*> peopleVector; vector<Person*>::iterator personIterator; int totalPeople; }; and the outputPeople function is defined as void PersonWrangler::outputPeople() { int totalConnections = 0; cout << " Total People:" << peopleVector.size() << endl; for (unsigned int i = 0;i < peopleVector.size();i++) { sort(peopleVector[i]->connectionsVector.begin(),peopleVector[i]->connectionsVector.end()); peopleVector[i]->connectionsVector.erase( unique (peopleVector[i]->connectionsVector.begin(),peopleVector[i]->connectionsVector.end()),peopleVector[i]->connectionsVector.end()); peopleVector[i]->outputPerson(); totalConnections+=peopleVector[i]->connectionsVector.size(); } cout << "Total connections:" << totalConnections/2 << endl; }

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  • Confused about std::runtime_error vs. std::logic_error

    - by David Gladfelter
    I recently saw that the boost program_options library throws a logic_error if the command-line input was un-parsable. That challenged my assumptions about logic_error vs. runtime_error. I assumed that logic errors (logic_error and its derived classes) were problems that resulted from internal failures to adhere to program invariants, often in the form of illegal arguments to internal API's. In that sense they are largely equivalent to ASSERT's, but meant to be used in released code (unlike ASSERT's which are not usually compiled into released code.) They are useful in situations where it is infeasible to integrate separate software components in debug/test builds or the consequences of a failure are such that it is important to give runtime feedback about the invalid invariant condition to the user. Similarly, I thought that runtime_errors resulted exclusively from runtime conditions outside of the control of the programmer: I/O errors, invalid user input, etc. However, program_options is obviously heavily (primarily?) used as a means of parsing end-user input, so under my mental model it certainly should throw a runtime_error in the case of bad input. Where am I going wrong? Do you agree with the boost model of exception typing?

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