abir basak wrote:
Hi, I am not sure if it is the proper newsgroup to get answers related to boost usage. I am facing a problem with boost::sub_range for a const container which is not allowing me to access the indexed operator. Below a short program to demonstrate the problem. Necessary headers are included. Boost version 1.33.1 typedef vector<int> VI; VI v(10); int data[] = {0,1,2,3,4,5,6,7,8,9}; copy(data,data+10,v.begin());///inserted a few int to std::vector<int>
Hm... this is not legal. It is "not legal" or "not preferred" ? I think it is legal, as I have a statement like VI v(10); rather than VI v; copy doesn't grow memory, or change size. But here I am just copying! Of course the other (and better ) way is, VI v; int data[] = {0,1,2,3,4,5,6,7,8,9}; v.assign(data,data+10);
May I suggest
v = boost::assign::list_of(0)(1)(2)(3)(4)(5)(6) ... ;
?
///prints 0 1 2 3 4 5 6 7 8 9 copy(v.begin(),v.end(),ostream_iterator<int>(cout," ")); cout<<endl; const VI& cv = v; /// a const reference to the container. VI::iterator it = v.begin(); ///got an random access iterator it[1] = 100; /// index operator allows to change it copy(v.begin(),v.end(),ostream_iterator<int>(cout," ")); cout<<endl; ///prints 0 100 2 3 4 ... VI::const_iterator it1 = v.begin(); ///got a const_iterator cout<<it1[1]<<endl; /// returns const_reference, assignment is not allowed, access is allowed. prints 100 boost::sub_range<VI> r(v.begin()+2,v.begin()+8); ///got a sub_range ///prints 2 3 4 5 6 7 copy(r.begin(),r.end(),ostream_iterator<int>(cout," ")); cout<<endl; r[2] = 400; cout<<r[2]<<endl;/// prints 400 ///prints 2 3 400 5 6 7 copy(r.begin(),r.end(),ostream_iterator<int>(cout," ")); ///so far everything is fine. Here problem starts /// a const sub_range ? boost::sub_range<const VI> r1(cv.begin()+2,cv.begin()+8); ///prints 2 3 400 5 6 7 copy(r1.begin(),r1.end(),ostream_iterator<int>(cout," "));cout<<endl; ///next statement is don't compile cout<<r1[2]<<endl; ///=> not allowed gives error under Visual Studio 7.1 cannot convert from 'const std::allocator<_Ty>::value_type' to 'boost::iterator_range<IteratorT>::value_type &' Why it tried to convert it to value_type& instead of const value_type& ? cout<<typeid(r1.begin()).name()<<endl; says r1.begin() is a const_iteartor. So the statement cout<<r1[2]<<endl; should return a const_reference. Am I mis interpreting the const version of sub_range ? If so, what is a const counterpart of sub_range, which behaves just like a pair of const_iterator ?
This is an error in the range lib that should be fixed in the upcoming version of boost. Is the correction is in the CVS head ? Or can you suggest what should be
Thorsten Ottosen wrote: the correction, if it is a small correction? Thanks for answering. abir
-Thorsten