stl - w3toppers.com

Order Statistic Tree in C++

Here is the example of GNU Policy-Based STL MAP implemented as order statistic tree (tested on Linux gcc 4.6.1): #include <iostream> #include <ext/pb_ds/assoc_container.hpp> #include <ext/pb_ds/tree_policy.hpp> using namespace std; using namespace __gnu_pbds; typedef tree< int, int, less<int>, rb_tree_tag, tree_order_statistics_node_update> map_t; int main() { map_t s; s.insert(make_pair(12, 1012)); s.insert(make_pair(505, 1505)); s.insert(make_pair(30, 1030)); cout << s.find_by_order(1)->second << ‘\n’; … Read more

STL map containing references does not compile

It is illegal to store references in an stl container, because types must be copy constructible and assignable. References can not be assigned. Exactly what operation causes the first error is implementation dependent, but I image that it is related to creating a reference and not assigning it immediately. The second error message looks like … Read more

const auto std::initializer_list difference between Clang and GCC

GCC bug. [dcl.spec.auto]/p7 (quoting N4527): When a variable declared using a placeholder type is initialized, […] the deduced return type or variable type is determined from the type of its initializer. […] Otherwise, let T be the declared type of the variable […]. If the placeholder is the auto type-specifier, the deduced type is determined … Read more

How to get the address of the std::vector buffer start most elegantly?

It’s really odd that nobody know this!!! in C++11 you could use: buffer.data() it could get the address of the vector I have test it: vector<char>buffer; buffer.push_back(‘w’); buffer.push_back(‘h’); buffer.push_back(‘a’); buffer.push_back(‘t’); buffer.push_back(‘\0’); char buf2[10]; memcpy(buf2,buffer.data(),10); Specification here.

Why does (i|o)fstream take a const char* parameter for a file name?

The string part of the library was developed after streams, and nobody thought to make the obvious modifications. It’s merely out of political and temporal reality that they never got around to this before shipping C++98, and nobody bothered bringing it up again because you could always solve it with .c_str(). C++0x fixes this (see … Read more

Why does stack not compile in g++? [duplicate]

The members of a standard container have to be copy assignable or movable (C++11). If the type is const it fails the requirements.

Insert into an STL queue using std::copy

Unfortunately std::queue ‘adapts’ the function known as push_back to just push which means that the standard back_insert_iterator doesn’t work. Probably the simplest way (albeit conceptually ugly) is to adapt the container adapter with a short lived container adapter adapter[sic] (eugh!) that lives as long as the back insert iterator. template<class T> class QueueAdapter { public: … Read more

STL algorithms: Why no additional interface for containers (additional to iterator pairs)?

They do introduce ambiguity for many algorithms. A lot of <algorithm> looks like template<class iterator> void do_something(iterator, iterator); template<class iterator, class funct> void do_something(iterator, iterator, funct); If you add additional overloads template<class container, class funct> void do_something(container, funct); the compiler will have some trouble figuring out what do_something(x, y) means. If x and y are … Read more

stl container with std::unique_ptr’s vs boost::ptr_container

I decided to write up a short program that put a few polymorphic objects into a container (by pointer to heap), and then use that container with a std::algorithm. I chose std::remove_if just as an example. Here is how I would do it with vector<unique_ptr<T>>: #include <vector> #include <memory> #include <iostream> class Animal { public: … Read more