stl

问题 This question already has answers here : Default constructor of the structure for correct std::map behaviour (2 answers) Closed 6 months ago . Consider the following class MyStruct : struct MyStruct { int x; int y; MyStruct(int i, int j): x(i), y(j) { } }; Note that MyStruct doesn't have a default destructor. The assignment m["AAAA"] = MyStruct(1, 1) in the code below doesn't compile: int main(int, char**) { map<string, MyStruct> m; m["AAAA"] = MyStruct(1, 1); return 0; } Why I need default

问题 I have a list of type struct and I want to remove a specific record from that list. What is the best way to do this? I cannot figure out how to do it with .remove struct dat { string s; int cnt; }; void StructList() { list<dat>::iterator itr; //-- create an iterator of type dat dat data1; //-- create a dat object list<dat> dList; //-- create a list of type dat itr = dList.begin(); //-- set the dList itereator to the begining of dList string temp; //-- temp string var for whatever data1.s =

问题 I have a list of type struct and I want to remove a specific record from that list. What is the best way to do this? I cannot figure out how to do it with .remove struct dat { string s; int cnt; }; void StructList() { list<dat>::iterator itr; //-- create an iterator of type dat dat data1; //-- create a dat object list<dat> dList; //-- create a list of type dat itr = dList.begin(); //-- set the dList itereator to the begining of dList string temp; //-- temp string var for whatever data1.s =

问题 Below is my code on set intersection and union test that I did. I don't understand why it the output is incorrect when I commented out the sort function. Why is the sort necessary? or am I missing anything here? What is the technical reason for making the programmer responsible to sort the inputs first? Is it for guaranteeing sorting is not done twice(if the vector was already sorted and the algorithm sorts it again...)? #include <iostream> #include <vector> #include <algorithm> using

问题 Below is my code on set intersection and union test that I did. I don't understand why it the output is incorrect when I commented out the sort function. Why is the sort necessary? or am I missing anything here? What is the technical reason for making the programmer responsible to sort the inputs first? Is it for guaranteeing sorting is not done twice(if the vector was already sorted and the algorithm sorts it again...)? #include <iostream> #include <vector> #include <algorithm> using

问题 Why is the time complexity required for swapping contents of two C++ STL vectors independent of the size of the corresponding vectors? Reference: http://www.cplusplus.com/reference/vector/vector/swap/ 回答1: A typical vector implementation stores: The allocator A pointer to the first element A pointer to the past-the-end position, or equivalently, the size A pointer to the end of the memory block owned by the vector, or equivalently, the capacity swap() simply swaps the pointers, and, if

问题 I've got two files: Header.h #pragma once #ifdef UNIQUEPTRISSUE_EXPORTS #define UNIQUEPTRISSUE_API __declspec(dllexport) #else #define UNIQUEPTRISSUE_API __declspec(dllimport) #endif UniquePtrIssue.cpp #include "stdafx.h" #include "Header.h" #include <memory> #include <vector> class UNIQUEPTRISSUE_API ClassA { }; class UNIQUEPTRISSUE_API ClassB { private: std::vector<std::unique_ptr<ClassA>> x; }; Compiling raises the following error: 1>d:\program files (x86)\microsoft visual studio\2017

问题 I was looking through some STL documentation. I see that the syntax for a priority queue which stores in a descending order is: std::priority_queue<int> q ; //gives 9 8 7 6 5 4 3 2 1 when pushed and obtained However, for storing in an ascending fashion, it's: std::priority_queue< int, std::vector<int>, std::greater<int> > q ; //gives 1 2 3 4 5 6 7 8 9 when pushed and obtained I want to know what are the specific uses of the extra template parameters in the second example. As in, what does std

问题 I was looking through some STL documentation. I see that the syntax for a priority queue which stores in a descending order is: std::priority_queue<int> q ; //gives 9 8 7 6 5 4 3 2 1 when pushed and obtained However, for storing in an ascending fashion, it's: std::priority_queue< int, std::vector<int>, std::greater<int> > q ; //gives 1 2 3 4 5 6 7 8 9 when pushed and obtained I want to know what are the specific uses of the extra template parameters in the second example. As in, what does std

问题 As we know, std::vector when initialized like std::vector vect(n) or empty_vect.resize(n) not only allocates required amount of memory but also initializes it with default value (i.e. calls default constructor). This leads to unnecessary initialization especially if I have an array of integers and I'd like to fill it with some specific values that cannot be provided via any vector constructor. Capacity on the other hand allocates the memory in call like empty_vect.reserve(n) , but in this