It doesn’t cause a crash, it just doesn’t compile. set doesn’t have access by index. You can get the nth element like this: std::set<int>::iterator it = my_set.begin(); std::advance(it, n); int x = *it; Assuming my_set.size() > n, of course. You should be aware that this operation takes time approximately proportional to n. In C++11 there’s … Read more
They way I understand it, references are implemented as pointers under the hood. The reason why you can’t store them in a map is purely semantic; you have to initialize a reference when it’s created and you can’t change it afterward anymore. This doesn’t mesh with the way a map works.
using: You are going to use it. namespace: To use what? A namespace. std: The std namespace (where features of the C++ Standard Library, such as string or vector, are declared). After you write this instruction, if the compiler sees string it will know that you may be referring to std::string, and if it sees … Read more
If you provide the deleter as template argument (as in unique_ptr) it is part of the type and you don’t need to store anything additional in the objects of this type. If deleter is passed as constructor’s argument (as in shared_ptr) you need to store it in the object. This is the cost of additional … Read more
The language specification allows implementations to implement <cmath> by declaring (and defining) the standard functions in global namespace and then bringing them into namespace std by means of using-declarations. It is unspecified whether this approach is used 20.5.1.2 Headers 4 […] In the C++ standard library, however, the declarations (except for names which are defined … Read more
Mingw uses the Windows API, and Windows doesn’t provide a conforming version of the vswprintf function used to implement to_string, blame Microsoft. If you use a (very) recent version of the mingw-w64 fork and the unreleased 4.8 version of GCC then it will work, but you’re outta luck with the main mingw32 and GCC 4.7.1 … Read more
Why are there parentheses after std::greater there? Are we creating a new std::greater object here? That’s correct. The expression std::greater<int>() corresponds to creating an object of type std::greater<int>. In that case, why don’t we need the new keyword here? We don’t need the new keyword because the object is being created on the stack, rather … Read more
Use std::sort and a functor. e.g: struct SortByX { bool operator() const (MyClass const & L, MyClass const & R) { return L.x < R.x; } }; std::sort(vec.begin(), vec.end(), SortByX()); The functor’s operator() should return true if L is less than R for the sort order you desire.
The compare function simply models a “less than” operator. Consider how the < operator works for primitive types like int: int a = 1, b = 2; a < b == true a is less than b int a = 2, b = 1; a < b == false a is not less than b, … Read more
I recommend against std::forward_list just like I recommend against std::list in almost all situations. Personally, I’ve never found a situation in my code where a linked list was the best data structure. In C++, your default go-to data collection should be std::vector. It gives you efficient push_back, if that is what you really need. It … Read more