I decided to test the solutions by dman and Charles Bailey here. I’ll call them solutions A and B respectively. My test is visiting each combination of of a vector<int> size = 100, 5 at a time. Here’s the test code: Test Code struct F { unsigned long long count_; F() : count_(0) {} bool … Read more
GCC typically has the standard C++ headers installed in /usr/include/c++/<version>/. You can run gcc -v to find out which version you have installed. At least in my version, there is no vector.h; the public header is just vector (with no extension), and most of the implementation is in bits/stl_vector.h. That’s the case on my Ubuntu … Read more
Boost is an open source project so the way I see it there are 2 options: Complain. Either write a bug report or get on the mailing list and suggest an enhancement or both. If the community thinks you have a good point, someone might take it on Do 1, then do something about it. … Read more
My system is set up as follows (Debian testing): libstdc++-7-dev: Installed: 7.2.0-16 libc++-dev: Installed: 3.5-2 clang: Installed: 1:3.8-37 g++: Installed: 4:7.2.0-1d1 I can confirm the bug when using libstdc++: g++ -o pois_gcc -std=c++11 pois.cpp clang++ -o pois_clang -std=c++11 -stdlib=libstdc++ pois.cpp clang++ -o pois_clang_libc -std=c++11 -stdlib=libc++ pois.cpp Result:
No, don’t roll your own. Instead, take a look at std::tuple – it’s a generalization of std::pair. So here’s a value-initialized triple of ints: std::tuple<int, int, int> triple; If you want, you can have a type alias for triples only: template<typename T1, typename T2, typename T3> using triple = std::tuple<T1, T2, T3>;
Is there any conceptual difference between std::optional<std::reference_wrapper<T>> and T*? std::optional<>, as the name already suggest, is meant to be used when we could have a value or might not have any value at all. The equivalent of having no value for a T* object would be assigning nullptr to it, i.e.: the pointer will point … Read more
This is basically Range v3’s group_by: group_by(v, std::equal_to{}). It doesn’t exist in the C++17 standard library, but we can write our own rough equivalent: template <typename FwdIter, typename BinaryPred, typename ForEach> void for_each_equal_range(FwdIter first, FwdIter last, BinaryPred is_equal, ForEach f) { while (first != last) { auto next_unequal = std::find_if_not(std::next(first), last, [&] (auto const& element) … Read more
None of the above answers are correct – in fact if you use fsetpos interchangeably with fseek you could introduce a security flaw (https://www.securecoding.cert.org/confluence/pages/viewpage.action?pageId=20087255). The reason is that the fpos_t *pos argument to fsetpos isn’t actually an integer so it can’t be used to seek to arbitrary locations in a file. The only valid values … Read more
The C99 draft standard does not explicitly state what should happen in those cases, but by considering multiple variations, you can show that it must work a certain way so that it meets the specification in all cases. The standard says: %s – Matches a sequence of non-white-space characters.252) If no l length modifier is … Read more
Interesting little question. According to the C++11 standard, sect. 21.4.2.9, basic_string(const charT* s, const Allocator& a = Allocator()); Requires: s shall not be a null pointer. Since the standard does not ask the library to throw an exception when this particular requirement is not met, it would appear that passing a null pointer provoked undefined … Read more