new-operator

问题 Why C++ hasn't placement delete that directly corresponds to the placement new, i.e. calls the destructor and calls appropriate placement delete operator? For example: MyType *p = new(arena) MyType; ... //current technique p->~MyType(); operator delete(p, arena); //proposed technique delete(arena) p; 回答1: operator delete is unique in being a non-member or static member function that is dynamically dispatched. A type with a virtual destructor performs the call to its own delete from the most

问题 How can I realloc in C++? It seems to be missing from the language - there is new and delete but not resize ! I need it because as my program reads more data, I need to reallocate the buffer to hold it. I don't think delete ing the old pointer and new ing a new, bigger one, is the right option. 回答1: Use ::std::vector! Type* t = (Type*)malloc(sizeof(Type)*n) memset(t, 0, sizeof(Type)*m) becomes ::std::vector<Type> t(n, 0); Then t = (Type*)realloc(t, sizeof(Type) * n2); becomes t.resize(n2); If

问题 What I want is: obj = Foo.new(0) # => nil or false This doesn't work: class Foo def initialize(val) return nil if val == 0 end end I know in C/C++/Java/C#, we cant return a value in a constructor. But I'm wondering whether it is possible in Ruby. 回答1: In Ruby, what's the relationship between ' new ' and ' initialize '? new typically calls initialize . The default implementation of new is something like: class Class def new(*args, &block) obj = allocate obj.initialize(*args, &block) # actually

问题 What I want is: obj = Foo.new(0) # => nil or false This doesn't work: class Foo def initialize(val) return nil if val == 0 end end I know in C/C++/Java/C#, we cant return a value in a constructor. But I'm wondering whether it is possible in Ruby. 回答1: In Ruby, what's the relationship between ' new ' and ' initialize '? new typically calls initialize . The default implementation of new is something like: class Class def new(*args, &block) obj = allocate obj.initialize(*args, &block) # actually

问题 In C++, Aside from dynamic memory allocation, is there a functional difference between the following two lines of code: Time t (12, 0, 0); //t is a Time object Time* t = new Time(12, 0, 0);//t is a pointer to a dynamically allocated Time object I am assuming of course that a Time(int, int, int) ctor has been defined. I also realize that in the second case t will need to be deleted as it was allocated on the heap. Is there any other difference? 回答1: The line: Time t (12, 0, 0); ... allocates a

问题 I learned C# first, and now I'm starting with C++. As I understand, operator new in C++ is not similar to the one in C#. Can you explain the reason of the memory leak in this sample code? class A { ... }; struct B { ... }; A *object1 = new A(); B object2 = *(new B()); 回答1: What is happening When you write T t; you're creating an object of type T with automatic storage duration . It will get cleaned up automatically when it goes out of scope. When you write new T() you're creating an object of

问题 I learned C# first, and now I'm starting with C++. As I understand, operator new in C++ is not similar to the one in C#. Can you explain the reason of the memory leak in this sample code? class A { ... }; struct B { ... }; A *object1 = new A(); B object2 = *(new B()); 回答1: What is happening When you write T t; you're creating an object of type T with automatic storage duration . It will get cleaned up automatically when it goes out of scope. When you write new T() you're creating an object of

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: C++'s “placement new” in the below code what does Line 3 represents, is it the way of typecasting? or what void someCode() { char memory[sizeof(Fred)]; // Line #1 void* place = memory; // Line #2 Fred* f = new(place) Fred(); // Line #3 // The pointers f and place will be equal ... } 回答1: This is a typical usage of Placement new . It allows you to allocate memory and then construct objects at that particular

问题 Say I have a pointer like this: int *thingy; At some point, this code may or may not be called: thingy=new int; How do I know if I can do this: delete thingy; I could use a bool for every pointer and mark the bool as true whenever the I use new , but I have many pointers and that would get very unwieldy. If I have not called new on thingy , calling delete on it would likely cause a crash, right? I searched around quite a bit but could find no answer that clearly fit my situation. EDIT: I need

问题 I have an NSMutablearray of objects. the number of objects is set by user. in c++ I would use a for cycle and the 'new' command.something like this: int fromuser, a; for(a=0;a<fromuser;a++){ array addobject:(new class obj) } what do I need to do in obj c since there is no new? 回答1: You would utilize the alloc and init (or more specialized initializer) provided by NSObject. For example, something like the following should work: int fromuser, a; NSMutableArray objectArray = [[NSMutableArray