If you have only 50 values in std::map you could copy them to std::vector before printing out and sort via std::sort using appropriate functor. Or you could use boost::multi_index. It allows to use several indexes. In your case it could look like the following: struct value_t { string s; int i; }; struct string_tag {}; … 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
It’s compiling because printf isn’t type safe, since it uses variable arguments in the C sense1. printf has no option for std::string, only a C-style string. Using something else in place of what it expects definitely won’t give you the results you want. It’s actually undefined behaviour, so anything at all could happen. The easiest … Read more
Here’s a working example based on the range-v3 Library that has been proposed for Standardization #include <range/v3/all.hpp> #include <iostream> using namespace ranges; int main() { std::vector<int> a1{15, 7, 3, 5}; std::vector<int> a2{ 1, 2, 6, 21}; sort(view::zip(a1, a2), std::less<>{}, &std::pair<int, int>::first); std::cout << view::all(a1) << ‘\n’; std::cout << view::all(a2) << ‘\n’; } Live Example (requires … 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
There are, indeed, performance issues with std:function that must be taken into account whenever using it. The main strength of std::function, namely, its type-erasure mechanism, does not come for free, and we might (but not necessarily must) pay a price for that. std::function is a template class that wraps callable types. However, it is not … Read more
template<class F> function(F f); template <class F, class A> function(allocator_arg_t, const A& a, F f); Requires: F shall be CopyConstructible. f shall be Callable for argument types ArgTypes and return type R. The copy constructor and destructor of A shall not throw exceptions. ยง20.9.11.2.1 [func.wrap.func.con] Note that operator = is defined in terms of this … Read more
You have to increment the iterator first (with i++) and then remove the previous element (e.g., by using the returned value from i++). You can change the code to a while loop like so: std::list<item*>::iterator i = items.begin(); while (i != items.end()) { bool isActive = (*i)->update(); if (!isActive) { items.erase(i++); // alternatively, i = … Read more
You can use std::find from <algorithm>: #include <algorithm> #include <vector> vector<int> vec; //can have other data types instead of int but must same datatype as item std::find(vec.begin(), vec.end(), item) != vec.end() This returns an iterator to the first element found. If not present, it returns an iterator to one-past-the-end. With your example: #include <algorithm> #include … Read more
There’s a function to find a substring within a string (find), and a function to replace a particular range in a string with another string (replace), so you can combine those to get the effect you want: bool replace(std::string& str, const std::string& from, const std::string& to) { size_t start_pos = str.find(from); if(start_pos == std::string::npos) return … Read more