stl

问题 Given a multimap<A,B> M what's a neat way to create a vector<B> of all values in M with a specific key. e.g given a multimap how can I get a vector of all strings mapped to the value 123? An answer is easy, looping from lower->upper bound, but is there a neat loop-free method? 回答1: Here's the way to do it STL style : // The following define is needed for select2nd with DinkumWare STL under VC++ #define _HAS_TRADITIONAL_STL 1 #include <algorithm> #include <vector> #include <map> #include

问题 Given an STL vector, output only the duplicates in sorted order, e.g., INPUT : { 4, 4, 1, 2, 3, 2, 3 } OUTPUT: { 2, 3, 4 } The algorithm is trivial, but the goal is to make it as efficient as std::unique(). My naive implementation modifies the container in-place: My naive implementation: void not_unique(vector<int>* pv) { if (!pv) return; // Sort (in-place) so we can find duplicates in linear time sort(pv->begin(), pv->end()); vector<int>::iterator it_start = pv->begin(); while (it_start !=

问题 I have such code which works well: #include <algorithm> #include <iostream> char x[11]= "ABCDEFGHIJ"; char y[11]; struct F { char operator () (char c) const { return c+1; } }; int main() { std::transform(x, x+10, y, F()); y[10] = 0; std::cout <<y <<std::endl; } But if I change it to this style: #include <algorithm> #include <iostream> char x[11]= "ABCDEFGHIJ"; char y[11]; int main() { struct F { char operator () (char c) const { return c+1; } }; std::transform(x, x+10, y, F()); y[10] = 0; std

问题 I have such code which works well: #include <algorithm> #include <iostream> char x[11]= "ABCDEFGHIJ"; char y[11]; struct F { char operator () (char c) const { return c+1; } }; int main() { std::transform(x, x+10, y, F()); y[10] = 0; std::cout <<y <<std::endl; } But if I change it to this style: #include <algorithm> #include <iostream> char x[11]= "ABCDEFGHIJ"; char y[11]; int main() { struct F { char operator () (char c) const { return c+1; } }; std::transform(x, x+10, y, F()); y[10] = 0; std

问题 When I make a std::map<my_data_type, mapped_value> , what C++ expects from me is that my_data_type has its own operator< . struct my_data_type { my_data_type(int i) : my_i(i) { } bool operator<(const my_data_type& other) const { return my_i < other.my_i; } int my_i; }; The reason is that you can derive operator> and operator== from operator< . b < a implies a > b , so there's operator> . !(a < b) && !(b < a) means that a is neither less than b nor greater than it, so they must be equal. The

问题 After C++11, various cmath functions previously in the global namespace are moved to the std namespace, when including the <cmath> header. However the android NDK build has issues with this, with both gcc-4.8 and clang-3.4 toolchains. The C++11 flag is correctly specified, as other c++11 particulars like unique_ptr work fine. If i attempt to use std::round , or std::cbrt , the compiler says these don't exist in std:: namespace, which they should [1]. They exist in the global namespace, but I

问题 I want to fill a vector with 8 pairs. Each pair represents the moves in x and y coordinates a knight in a game of chess can make. At the moment I'm doing it like this vector<pair<int,int>> moves; pair<int,int> aPair; aPair.first = -2; aPair.second = -1; moves.push_back(aPair); aPair.first = -2; aPair.second = 1; moves.push_back(aPair); aPair.first = -1; aPair.second = -2; moves.push_back(aPair); aPair.first = -1; aPair.second = 2; moves.push_back(aPair); aPair.first = 1; aPair.second = -2;

问题 Over time various alternative implementations of the STL* have appeared - such as STLPort. Certain large corporations also use their own internal port of the STL for various purposes. With C++03, it's possible to write a port of the STL using only portable C++ language features, meaning that any conforming compiler should be able to compile it. But with C++11, aren't there certain features which require compiler support? For example, I don't see how std::is_standard_layout could be

问题 What is the difference between the front() and begin() functions that appears in many STL containers? 回答1: begin() returns an iterator that can be used to iterate through the collection, while front() just returns a reference to the first element of the collection. 回答2: front() returns a reference to the first element, begin() returns an iterator to it. Note that you shouldn't call front on an empty container, but it's OK to call begin as long as you don't dereference the iterator that begin

问题 This question already has answers here : small string optimization for vector? (4 answers) Closed 4 years ago . In one time-critical part of the program there is a member of the class that looks like that: std::vector m_vLinks; During profiling I noticed that about 99.98% of executions this vector holds only 0 or 1 items. However in very rarely cases it might hold more. This vector is definitely a bottleneck according to profiler, so I'm thinking about following optimization: Craft a hand