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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • Embarassing C++ question regarding const

    - by Neil Butterworth
    My comments on this answer got me thinking about the issues of constness and sorting. I played around a bit and reduced my issues to the fact that this code: #include <vector> int main() { std::vector <const int> v; } will not compile - you can't create a vector of const ints. I suppose I should have known this, but I've never needed to create such a thing before. However, it seems like a useful construct to me, and I wonder if there is any way round this problem - I want to add things to a vector (or whatever), but they should not be changed once added. There's probably some embarrassingly simple solution to this, but it's something I'd never considered before.

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  • Could this C cast to avoid a signed/unsigned comparison make any sense?

    - by sharptooth
    I'm reviewing a C++ project and see effectively the following: std::vector<SomeType> objects; //then later int size = (int)objects.size(); for( int i = 0; i < size; ++i ) { process( objects[i] ); } Here's what I see. std::vector::size() returns size_t that can be of some size not related to the size of int. Even if sizeof(int) == sizeof(size_t) int is signed and can't hold all possible values of size_t. So the code above could only process the lower part of a very long vector and contains a bug. That said I'm curious of why the author might have written this? My only guess is that first he omitted the (int) cast and the compiler emitted something like Visual C++ C4018 warning: warning C4018: '<' : signed/unsigned mismatch so the author though that the best way to avoid the compiler warning would be to simply cast the size_t to int thus making the compiler shut up. Is there any other possible sane reason for that C cast?

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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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  • Using pair in c++

    - by user1543957
    Can someone please tell why i am unable to compile the following program #include<iostream> #include<string> #include<cmath> #include<iostream> #include<cfloat> #define MOD 10000009 using namespace std; double distance(pair<int,int> p1,pair<int,int> p2) { double dist; dist = sqrt( (p1.first-p2.first)*(p1.first-p2.first) + (p1.second-p2.second)*(p1.second-p2.second) ); return(dist); } int main() { int N,i,j; cin >> N; pair<int,int> pi[N]; for(i=0;i<N;i++) { cin >> pi[i].first >> pi[i].second; } for(i=0;i<N;i++) { cout << pi[i].first << " "<< pi[i].second << endl; } distance(pi[0],pi[1]); // This line is giving error return 0; }

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  • creating a vector with references to some of the elements of another vector

    - by memC
    hi, I have stored instances of class A in a std:vector, vec_A as vec_A.push_back(A(i)). The code is shown below. Now, I want to store references some of the instances of class A (in vec_A) in another vector or another array. For example, if the A.getNumber() returns 4, 7, 2 , I want to put a reference to that instance of A in another vector, say std:vector<A*> filtered_A or an array. Can someone sow me how to do this?? Thanks! class A { public: int getNumber(); A(int val); ~A(){}; private: int num; }; A::A(int val){ num = val; }; int A::getNumber(){ return num; }; int main(){ int i =0; int num; std::vector<A> vec_A; for ( i = 0; i < 10; i++){ vec_A.push_back(A(i)); } std::cout << "\nPress RETURN to continue..."; std::cin.get(); return 0; }

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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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  • Finding minimum value in a Map

    - by Sunny
    I have a map and I want to find the minimum value (right hand side) in the map. Right now here is how I did it bool compare(std::pair<std::string ,int> i, pair<std::string, int> j) { return i.second < j.second; } //////////////////////////////////////////////////// std::map<std::string, int> mymap; mymap["key1"] = 50; mymap["key2"] = 20; mymap["key3"] = 100; std::pair<char, int> min = *min_element(mymap.begin(), mymap.end(), compare); std::cout << "min " << min.second<< " " << std::endl; This works fine and I'm able to get the minimum value the problem is when I put this code inside my class it doesn't seem to work int MyClass::getMin(std::map<std::string, int> mymap) { std::pair<std::string, int> min = *min_element(mymap.begin(), mymap.end(), (*this).compare); //error probably due to this return min.second; } bool MyClass::compare( std::pair<std::string, int> i, std::pair<std::string, int> j) { return i.second < j.second; } Also is there a better solution not involving to writing the additional compare function

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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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  • Is there a way to intersect/diff a std::map and a std::set?

    - by Jack
    I'm wondering if there a way to intersect or make the differences between two structures defined as std::set<MyData*> and std::map<MyData*, MyValue> with standard algorithms (like std::set_intersect) The problem is that I need to compute the difference between the set and the keyset of the map but I would like to avoid reallocating it (since it's something that is done many times per second with large data structures). Is there a way to obtain a "key view" of the std::map? After all what I'm looking is to consider just the keys when doing the set operation so from an implementation point it should be possible but I haven't been able to find anything.

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  • c++ template function compiles in header but not implementation

    - by flies
    I'm trying to learn templates and I've run into this confounding error. I'm declaring some functions in a header file and I want to make a separate implementation file where the functions will be defined. Here's the code that calls the header (dum.cpp): #include <iostream> #include <vector> #include <string> #include "dumper2.h" int main() { std::vector<int> v; for (int i=0; i<10; i++) { v.push_back(i); } test(); std::string s = ", "; dumpVector(v,s); } now, here's a working header file (dumper2.h): #include <iostream> #include <string> #include <vector> void test(); template <class T> void dumpVector( std::vector<T> v,std::string sep); template <class T> void dumpVector(std::vector<T> v, std::string sep) { typename std::vector<T>::iterator vi; vi = v.begin(); std::cout << *vi; vi++; for (;vi<v.end();vi++) { std::cout << sep << *vi ; } std::cout << "\n"; return; } with implentation (dumper2.cpp): #include <iostream> #include "dumper2.h" void test() { std::cout << "!olleh dlrow\n"; } the weird thing is that if I move the code that defines dumpVector from the .h to the .cpp file, I get the following error: g++ -c dumper2.cpp -Wall -Wno-deprecated g++ dum.cpp -o dum dumper2.o -Wall -Wno-deprecated /tmp/ccKD2e3G.o: In function `main': dum.cpp:(.text+0xce): undefined reference to `void dumpVector<int>(std::vector<int, std::allocator<int> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)' collect2: ld returned 1 exit status make: *** [dum] Error 1 So why does it work one way and not the other? Clearly the compiler can find test(), so why can't it find dumpVector?

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