Hi, I have a question related to the boost::shared_ptr constructor. I want to be able to store boost::shared_ptr<Base> objects in a std::vector. However, I don't want to bother my users with the fact (implementation detail) that I'm using shared_ptrs instead of raw pointers. The simplified sample code below more or less clarifies what I want. The code in line 27 is the code I would like to be able to use. Below that line, several attempts to get the code to compile can be found. I understand that line 32 won't compile, because it is equivalent to line 27. However, line 37 left me puzzled. I would expect that the conversion of B* to shared_ptr<B> would be trivial. Not so. Is it really true that the only way to use shared_ptr in the way I want is as in lines 46, 47? Or am I overlooking something? And is line 41 equivalent to line 46? Thanks in advance. Regards, Marcel Loose. P.S.: I noticed that all code will compile if I omit the "explicit" keyword in the constructor of shared_ptr, but I don't consider that the proper way to solve the problem. 1:#include <boost/shared_ptr.hpp> 2:#include <vector> 3: 4:using namespace std; 5:using namespace boost; 6: 7:class Base 8:{ 9:public: 10: Base() { /* ... */ } 11: virtual ~Base() {} 12:}; 13: 14:class Derived : public Base 15:{ 16:public: 17: Derived() { /* ... */ } 18: virtual ~Derived() {} 19:}; 20: 21: 22:int main() 23:{ 24: vector<shared_ptr<Base> > v; 25: 26: { // failes to compile: 27: v.push_back(new Derived()); // cannot convert Derived*& 28: } // to shared_ptr<Base>. Why? 29: 30: { // failes to compile: 31: Derived* d(new Derived()); // cannot convert Derived*& 32: v.push_back(d); // to shared_ptr<Base>. Why? 33: } 34: 35: { // failes to compile: 36: Base* b(new Derived()); // cannot convert Base*& 37: v.push_back(b); // to shared_ptr<Base>. Huh? 38: } // Seems a trivial conversion. 39: 40: { // OK, this compiles, but is 41: shared_ptr<Derived> d(new Derived()); // it correct? I.e. is conversion 42: v.push_back(d); // shared_ptr<Derived> to 43: } // shared_ptr<Base> trivial? 44: 45: { // OK, this compiles, and is 46: shared_ptr<Base> b(new Derived()); // probably what I meant. 47: v.push_back(b); // However, I dislike the 48: } // verbosity. 49: 50: return 0; 51:} Just to be complete, please find the compiler diagnostics below. tBoost.cc: In function `int main()': tBoost.cc:27: no matching function for call to ` std::vector<boost::shared_ptr<Base>, std::allocator<boost::shared_ptr<Base>
::push_back(Derived*&)' /usr/local/gcc-3.2.1/include/c++/3.2.1/bits/stl_vector.h:490: candidates are: void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = boost::shared_ptr<Base>, _Alloc = std::allocator<boost::shared_ptr<Base> >] tBoost.cc:32: no matching function for call to ` std::vector<boost::shared_ptr<Base>, std::allocator<boost::shared_ptr<Base> ::push_back(Derived*&)' /usr/local/gcc-3.2.1/include/c++/3.2.1/bits/stl_vector.h:490: candidates are: void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = boost::shared_ptr<Base>, _Alloc = std::allocator<boost::shared_ptr<Base> >] tBoost.cc:37: no matching function for call to ` std::vector<boost::shared_ptr<Base>, std::allocator<boost::shared_ptr<Base> ::push_back(Base*&)' /usr/local/gcc-3.2.1/include/c++/3.2.1/bits/stl_vector.h:490: candidates are: void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = boost::shared_ptr<Base>, _Alloc = std::allocator<boost::shared_ptr<Base> >]