I think the previous answers are misleading. fstream is a proper RAII object, it does close automatically at the end of the scope, and there is absolutely no need whatsoever to call close manually when closing at the end of the scope is sufficient. In particular, it’s not a “best practice” and it’s not necessary … Read more
In Visual Studio you must #include “stdafx.h” and be the first include of the cpp file. For instance: These will not work. #include <iostream> using namespace std; int main () { cout << “hey” << endl; return 0; } #include <iostream> #include “stdafx.h” using namespace std; int main () { cout << “hey” << endl; … Read more
You should think of using std::ref when a function: takes a template parameter by value copies/moves a template parameter, such as std::bind or the constructor for std::thread. std::ref creates a copyable value type that behaves like a reference. This example makes demonstrable use of std::ref. #include <iostream> #include <functional> #include <thread> void increment( int &x … Read more
On Linux: In general, all commonly available linux distributions will use libstdc++ by default, and all modern versions of GCC come with a libstdc++ that supports C++11. If you want to compile c++11 code here, use one of: g++ -std=c++11 input.cxx -o a.out (usually GNU compiler) g++ -std=gnu++11 input.cxx -o a.out On OS X before … Read more
Your using declaration is in game.cpp, not game.h where you actually declare string variables. You intended to put using namespace std; into the header, above the lines that use string, which would let those lines find the string type defined in the std namespace. As others have pointed out, this is not good practice in … Read more
Okay, here you go: std::vector<Key> keys; keys.reserve(map.size()); std::vector<Val> vals; vals.reserve(map.size()); for(auto kv : map) { keys.push_back(kv.first); vals.push_back(kv.second); } Efficiency can probably be improved, but there it is. You’re operating on two containers though, so there’s not really any STL magic that can hide that fact. As Louis said, this will work for any of the … Read more
Use the std::vector::insert function accepting an iterator to the first element as a target position (iterator before which to insert the element): #include <vector> int main() { std::vector<int> v{ 1, 2, 3, 4, 5 }; v.insert(v.begin(), 6); } Alternatively, append the element and perform the rotation to the right: #include <vector> #include <algorithm> int main() … Read more
The std::string::append() method expects its argument to be a NULL terminated string (char*). There are several approaches for producing a string containg an int: std::ostringstream #include <sstream> std::ostringstream s; s << “select logged from login where id = ” << ClientID; std::string query(s.str()); std::to_string (C++11) std::string query(“select logged from login where id = ” + … Read more
Even though correct answers have already been posted, I thought I’d add a demo of how you can do this cleanly: template<typename A, typename B> std::pair<B,A> flip_pair(const std::pair<A,B> &p) { return std::pair<B,A>(p.second, p.first); } template<typename A, typename B> std::multimap<B,A> flip_map(const std::map<A,B> &src) { std::multimap<B,A> dst; std::transform(src.begin(), src.end(), std::inserter(dst, dst.begin()), flip_pair<A,B>); return dst; } int main(void) … Read more
Is it possible that you are using GCC 5? If you get linker errors about undefined references to symbols that involve types in the std::__cxx11 namespace or the tag [abi:cxx11] then it probably indicates that you are trying to link together object files that were compiled with different values for the _GLIBCXX_USE_CXX11_ABI macro. This commonly … Read more