reference

问题 For both std::map and std::tr1::unordered_map , I see from the standard that: References to elements in the unordered_map container remain valid in all cases, even after a rehash. How are they doing that ( implementation-wise )? Are they maintaining all the entries as a kind of linked list and then the hash-table just stores pointers to the elements? 回答1: Yes, linked lists are involved, although not quite in the way you suggest. The 2011 standard says (23.2.5 para 8), "The elements of an

问题 This question already has answers here : How do you remove an array element in a foreach loop? (8 answers) Closed 3 years ago . I'm accessing an array by reference inside a foreach loop, but the unset() function doesn't seem to be working: foreach ( $this->result['list'] as &$row ) { if ($this_row_is_boring) { unset($row); } } print_r($this->result['list']); // Includes rows I thought I unset Ideas? Thanks! 回答1: You're unsetting the reference (breaking the reference). You'd need to unset

问题 I am trying to consume a WCF service in a class library by adding a service reference to it. In one of the class libraries it gets consumed properly and I can access the client types in order to generate a proxy off of them. However in my second class library (or even in a console test app), when i add the same service reference, it only exposes the types that are involved in the contract operations and not the client type for me to generate a proxy against. e.g. Endpoint has 2 services

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 21 days ago . OpenSSL documents state that it can safely be used in multi-threaded applications provided that at least two callback functions are set, locking_function and threadid_func.... I've written programs which use OpenSSL API. Moreover, I know how to use pthreads. However, the OpenSSL documents are written in the form

问题 Why does returning the reference to a pointed-to member variable work, but not the other? I know that a const member function should only return const references, but why does that not seem true for pointers? class MyClass { private: int * a; int b; public: MyClass() { a = new int; } ~MyClass() { delete a; } int & geta(void) const { return *a; } // good? int & getb(void) const { return b; } // obviously bad }; int main(void) { MyClass m; m.geta() = 5; //works???? m.getb() = 7; //doesn't

问题 Question about why is it necessary at all to return a reference from a function. Following code behaves exactly the same, if we replace int& with int in line9 and line16. Is it true in my example code, returning reference vs value doesnt matter? In what kind of example it will start to matter? In my mind, we cant return the reference of a local variable of the function, since the local variable will be out of scope for the caller. Therefore, it only make sense to return a reference of a

问题 Question about why is it necessary at all to return a reference from a function. Following code behaves exactly the same, if we replace int& with int in line9 and line16. Is it true in my example code, returning reference vs value doesnt matter? In what kind of example it will start to matter? In my mind, we cant return the reference of a local variable of the function, since the local variable will be out of scope for the caller. Therefore, it only make sense to return a reference of a

问题 I have a concept I hope you can help to clarify: What's the difference between the following three ways of referring to a column in PySpark dataframe. I know different situations need different forms, but not sure why. df.col : e.g. F.count(df.col) df['col'] : e.g. df['col'] == 0 F.col('col') : e.g. df.filter(F.col('col').isNull()) Thanks a lot! 回答1: In most practical applictions, there is almost no difference. However, they are implemented by calls to different underlying functions (source)

问题 The java memory model mandates that writing a int is atomic: That is, if you write a value to it (consisting of 4 bytes) in one thread and read it in another, you will get all bytes or none, but never 2 new bytes and 2 old bytes or such. This is not guaranteed for long . Here, writing 0x1122334455667788 to a variable holding 0 before could result in another thread reading 0x112233440000000 or 0x0000000055667788 . Now the specification does not mandate object references to be either int or

问题 The java memory model mandates that writing a int is atomic: That is, if you write a value to it (consisting of 4 bytes) in one thread and read it in another, you will get all bytes or none, but never 2 new bytes and 2 old bytes or such. This is not guaranteed for long . Here, writing 0x1122334455667788 to a variable holding 0 before could result in another thread reading 0x112233440000000 or 0x0000000055667788 . Now the specification does not mandate object references to be either int or