How to find if a given key exists in a C++ std::map
Use map::find and map::end: if (m.find(“f”) == m.end()) { // not found } else { // found }
stl
How do I erase an element from std::vector by index?
To delete a single element, you could do: std::vector<int> vec; vec.push_back(6); vec.push_back(-17); vec.push_back(12); // Deletes the second element (vec[1]) vec.erase(std::next(vec.begin())); Or, to delete more than one element at once: // Deletes the second through third elements (vec[1], vec[2]) vec.erase(std::next(vec.begin(), 1), std::next(vec.begin(), 3));
What is the easiest way to initialize a std::vector with hardcoded elements?
If your compiler supports C++11, you can simply do: std::vector<int> v = {1, 2, 3, 4}; This is available in GCC as of version 4.4. Unfortunately, VC++ 2010 seems to be lagging behind in this respect. Alternatively, the Boost.Assign library uses non-macro magic to allow the following: #include <boost/assign/list_of.hpp> … std::vector<int> v = boost::assign::list_of(1)(2)(3)(4); Or: … Read more
Appending a vector to a vector [duplicate]
a.insert(a.end(), b.begin(), b.end()); or a.insert(std::end(a), std::begin(b), std::end(b)); The second variant is a more generically applicable solution, as b could also be an array. However, it requires C++11. If you want to work with user-defined types, use ADL: using std::begin, std::end; a.insert(end(a), begin(b), end(b));
Concatenating two std::vectors
vector1.insert( vector1.end(), vector2.begin(), vector2.end() );
push_back vs emplace_back
In addition to what visitor said : The function void emplace_back(Type&& _Val) provided by MSCV10 is non conforming and redundant, because as you noted it is strictly equivalent to push_back(Type&& _Val). But the real C++0x form of emplace_back is really useful: void emplace_back(Args&&…); Instead of taking a value_type it takes a variadic list of arguments, … Read more