vector

问题 I need to read in lines from a given text file into a vector of a class of strings. I have this so far but I cannot get them into the vector. I am trying to create a while loop to read in each line of the text file input by the user. I've modified it from the last time, but all it does is read in one thing at a time, splitting Las and Vegas. I also need to push the information from my text file into my Flight vector. #include "sort.h" #include "flight.h" #include "std_lib_facilities_4.h"

问题 In my textbook, the implementation of the vector push_back move implementation is: void push_back( Object && x ) { if( theSize == theCapacity ) reserve( 2 * theCapacity + 1 ); objects[ theSize++ ] = std::move( x ); } My understanding of std::move is that it basically static casts the item as an rvalue reference. So why on the last line did they have to use std::move( x ), when x was passed in already as an rvalue reference? 回答1: x is an rvalue reference, but the rule of thumb you must follow

问题 In my textbook, the implementation of the vector push_back move implementation is: void push_back( Object && x ) { if( theSize == theCapacity ) reserve( 2 * theCapacity + 1 ); objects[ theSize++ ] = std::move( x ); } My understanding of std::move is that it basically static casts the item as an rvalue reference. So why on the last line did they have to use std::move( x ), when x was passed in already as an rvalue reference? 回答1: x is an rvalue reference, but the rule of thumb you must follow

问题 In my textbook, the implementation of the vector push_back move implementation is: void push_back( Object && x ) { if( theSize == theCapacity ) reserve( 2 * theCapacity + 1 ); objects[ theSize++ ] = std::move( x ); } My understanding of std::move is that it basically static casts the item as an rvalue reference. So why on the last line did they have to use std::move( x ), when x was passed in already as an rvalue reference? 回答1: x is an rvalue reference, but the rule of thumb you must follow

问题 In my textbook, the implementation of the vector push_back move implementation is: void push_back( Object && x ) { if( theSize == theCapacity ) reserve( 2 * theCapacity + 1 ); objects[ theSize++ ] = std::move( x ); } My understanding of std::move is that it basically static casts the item as an rvalue reference. So why on the last line did they have to use std::move( x ), when x was passed in already as an rvalue reference? 回答1: x is an rvalue reference, but the rule of thumb you must follow

问题 Consider the following code: let u: Vec<u8> = (64..74).collect(); let v: Vec<u8> = u.iter().map(|i| i + 1).collect(); u was not moved, therefore v was inevitably newly allocated. But if I do the following: let w: Vec<u8> = u.into_iter().map(|i| i + 1).collect(); u was moved and w is the name of its transformation. Here is some pseudo-code representing what I mean: mark u as "moved" for i = 0..10: u[i] += 1 w = u There is (in my opinion) no need for a new allocation, since we map a type to

问题 Have there been any reliable tests that clearly display the performance differences between accessing and writing to nested vectors versus C++'s built-in arrays? I've heard that using nested (multi-dimensional) vectors typically have some performance overhead as compared to accessing elements in a single array (where all elements are stored in contiguous memory), but this just all seems to be hypothetical to me. I have yet to see any tests that actually show these differences. Are they

问题 On an online course I am learning about vectors. In one of the examples they explained that: std::vector::max_size() should give me the maximum size the vector can reach. I decided to test it: #include <iostream> #include <exception> #include <vector> int main(void) { std::vector <int> nums; int max = nums.max_size(); std::cout << "Max: " << max << std::endl; for (int i = 0; i < max; i++) { try { nums.push_back(i); } catch (std::bad_alloc ex) { std::cerr << ex.what() << std::endl; std::cout <

问题 On an online course I am learning about vectors. In one of the examples they explained that: std::vector::max_size() should give me the maximum size the vector can reach. I decided to test it: #include <iostream> #include <exception> #include <vector> int main(void) { std::vector <int> nums; int max = nums.max_size(); std::cout << "Max: " << max << std::endl; for (int i = 0; i < max; i++) { try { nums.push_back(i); } catch (std::bad_alloc ex) { std::cerr << ex.what() << std::endl; std::cout <

问题 This question already has answers here : How do I sort a vector of pairs based on the second element of the pair? (7 answers) Closed 6 years ago . vector<pair<int,int> > v; for(i=0;i<5;i++){ cin>>b>>c; v.push_back(make_pair(b,c)); } sort(v.begin(),v.end()); Is it possible to write a comparator for the sort function such that v[i].first is sorted in increasing order and for similar values of v[i].first , v[i].second is sorted in decreasing order? like:- i/p: 13 10 44 15 13 15 13 99 6 45 o/p: 6