new-operator

问题 I'm reading to brush up on C++ knowledge that is almost 2 decades old in order to understand online info on the factory pattern. The final usage context will likely be in a different 3rd generation language (3GL), but because of my past experience, I think it's easier to follow C++ than (say) Java, even though the latter may be less intricate in syntax. A bigger reason, however, is that the only code example I can find of the problem being addressed, i.e., in the absence of the factory

问题 I'm reading to brush up on C++ knowledge that is almost 2 decades old in order to understand online info on the factory pattern. The final usage context will likely be in a different 3rd generation language (3GL), but because of my past experience, I think it's easier to follow C++ than (say) Java, even though the latter may be less intricate in syntax. A bigger reason, however, is that the only code example I can find of the problem being addressed, i.e., in the absence of the factory

问题 This is the solution to printing elements of a linked list. Why isn't it Node *current = new Node; and then current = head; ? void printLinkedList(Node* head) { Node *current = head; while(current!=NULL){ cout << current -> data << endl; current = current -> next; } } 回答1: This is a great spot to draw pictures! Imagine we have a linked list pointed at by head : head | v +------+ +-----+ +-----+ +-----+ | i'm | -> | the | -> | bad | -> | guy | -> null +------+ +-----+ +-----+ +-----+ If we use

问题 These days I am struggling at malloc memory. I try to read 16-bit binary data from raw img and store them in buffer or vector. The total size of these binary data is about 15M. For this kind of size, which way is better between buf or vector? Here is my code below: #include <imebra/imebra.h> #include <stdio.h> #include <iostream> #include <fstream> #include <string.h> #include <vector> #include<iterator> #include <algorithm> #define img_height 2816 #define img_width 2816 //#define img_size

问题 In java, can I use a class object to dynamically instantiate classes of that type? i.e. I want some function like this. Object foo(Class type) { // return new object of type 'type' } 回答1: In Java 9 and afterward, if there's a declared zero-parameter ("nullary") constructor, you'd use Class.getDeclaredConstructor() to get it, then call newInstance() on it: Object foo(Class type) throws InstantiationException, IllegalAccessException, InvocationTargetException { return type

问题 A simple test app: cout << new int[0] << endl; outputs: 0x876c0b8 So it looks like it works. What does the standard say about this? Is it always legal to "allocate" empty block of memory? 回答1: From 5.3.4/7 When the value of the expression in a direct-new-declarator is zero, the allocation function is called to allocate an array with no elements. From 3.7.3.1/2 The effect of dereferencing a pointer returned as a request for zero size is undefined. Also Even if the size of the space requested

问题 I've read many threads with questions which looks like questions I am going to ask. However, I can not find satisfactory answers which could be applied to my questions, since there are more than one fold in my questions, seperated in three aspects. This is the interface SubtitleDecoderFactory in https://github.com/google/ExoPlayer/blob/release-v2/library/core/src/main/java/com/google/android/exoplayer2/text/SubtitleDecoderFactory.java As I understand, an interace is abstraction and can not

问题 char * buf = new char[sizeof(T)]; new (buf) T; T * t = (T *)buf; //code... //here I should destruct *t but as it is argument of template and can be //instantiated via basic types as well (say int) so such code /*t->~T();*/ //is incorrect (maybe correct? Strange, but it works on VS 2005 for basic types.) //and this code /*delete t;*/ //crashes the program. delete [] buf; So what is correct way to destruct t ? P.S. The code above is only for describing my problem, and have not real relationship

问题 char * buf = new char[sizeof(T)]; new (buf) T; T * t = (T *)buf; //code... //here I should destruct *t but as it is argument of template and can be //instantiated via basic types as well (say int) so such code /*t->~T();*/ //is incorrect (maybe correct? Strange, but it works on VS 2005 for basic types.) //and this code /*delete t;*/ //crashes the program. delete [] buf; So what is correct way to destruct t ? P.S. The code above is only for describing my problem, and have not real relationship

问题 char * buf = new char[sizeof(T)]; new (buf) T; T * t = (T *)buf; //code... //here I should destruct *t but as it is argument of template and can be //instantiated via basic types as well (say int) so such code /*t->~T();*/ //is incorrect (maybe correct? Strange, but it works on VS 2005 for basic types.) //and this code /*delete t;*/ //crashes the program. delete [] buf; So what is correct way to destruct t ? P.S. The code above is only for describing my problem, and have not real relationship