casting

问题 I am trying to emulate the way fortran reads data from text files in C#. In fortran you have something like READ(60,2005,ERR=9880,END=8000) A,B,C,D 2005 FORMAT(I8,A20,2F10.3) and A, B, C, D are automatically set to the correct type based on the format statement. I have tried things along the lines of: private static void Example(string[] Data, ref object[] Variables) { for (int i = 0; i < Data.Length; i++) Variables[i] = (typeof(Variables[i]))Data; } but can't even get code that will compile.

问题 I have int* foo[SIZE] and I want to search it for the first element that points to NULL . But when I do this: std::find(foo, foo + SIZE, NULL) I get the error: error C2446: '==' : no conversion from 'const int' to 'int *' Should I just be using static_cast<int*>(NULL) instead of NULL ? C++11 solves this via nullptr but that's not an option for me in C++03 回答1: tl;dr: Use nullptr , or define your own equivalent. The problem is that NULL is some macro that expands to an integral constant

问题 Why is the type cast operator (as) being used instead of its conditional form (as?) in this switch statement? I thought the type operator could only be (as?) or (as!)...? The Apple Swift documentation does not provide adequate explanation about this. Here is the example in the Swift documentation: var things = [Any]() things.append(0) things.append(0.0) things.append(42) things.append(3.14159) things.append("hello") things.append((3.0, 5.0)) things.append(Movie(name: "Ghostbusters", director:

问题 Latest version of Objective-C and XCode (4.4). I have a code snippet and I cannot understand why I'm able to use some lines, let me explain : // For understanding purpose : (NSMutableArray*)_programStack id l_topItemOnStack = [_programStack lastObject]; if([l_topItemOnStack isKindOfClass:[NSNumber class]]) { return [l_topItemOnStack doubleValue]; } My question : since my l_topItemOnStack is of type id and I didn't cast it into a NSNumber , how am i able to use the [l_topItemOnStack

问题 I tried extracting all the digits out of a 20 character string by using REGEXP_SUBSTR Sql function like below. select REGEXP_SUBSTR(substring(mycolumn,1,20), '^[0-9]', 1) || REGEXP_SUBSTR(substring(mycolumn,1,20), '^[0-9]', 2) || REGEXP_SUBSTR(substring(mycolumn,1,20), '^[0-9]', 3) ... ... || REGEXP_SUBSTR(substring(mycolumn,1,20), '^[0-9]', 20) from tbl; But when trying to cast it as bigint / decimal or any numeric data type it is failing with Invalid input syntax for type numeric or Invalid

问题 Eclipse says: Type safety: Unchecked cast from Object to ObjectArrayList<Car> when I do: final ObjectArrayList<Car> icars = (ObjectArrayList<Car>) cars[i]; where cars is defined as: final Object[] cars = new Object[1000]; for (int i = 0; i < 1000; i++) { cars[i] = new ObjectArrayList<Car>(); } Eclipse suggests to add @SuppressWarnings("unchecked") to icars object. But I've read somewhere that annotations are deprecated in Java, so should I leave it as it is? 回答1: The warning is just, well,

问题 In Kotlin I can: val (specificMembers, regularMembers) = members.partition {it is SpecificMember} However to my knowledge I can not do something like: val (specificMembers as List<SpecificMember>, regularMembers) = members.partition {it is SpecificMember} My question would be - is there's an idiomatic way to partition iterable by class and typecast it those partitioned parts if needed. 回答1: The partition function will return a Pair<List<T>, List<T>> with T being the generic type of your

问题 In Kotlin I can: val (specificMembers, regularMembers) = members.partition {it is SpecificMember} However to my knowledge I can not do something like: val (specificMembers as List<SpecificMember>, regularMembers) = members.partition {it is SpecificMember} My question would be - is there's an idiomatic way to partition iterable by class and typecast it those partitioned parts if needed. 回答1: The partition function will return a Pair<List<T>, List<T>> with T being the generic type of your

问题 I'm writing a simple implementation of a generic max heap. If I write public class FastMaxHeap<T>{ T[] data; int size; static final int HEAP_SIZE = 10000; @SuppressWarnings("unchecked") public FastMaxHeap(){ data = (T[]) new Object[HEAP_SIZE]; size = 0; } } it compiles. Now to actually implement the heap, i.e. write maxHeapify(), I need to be able to compare two T's. One option that a priori seems possible would be to tell the compiler that T implements Comparable. But if I type replace < T >

问题 class A { int i = 1; int f() { return i; } } class B extends A { int i = 2; int @Override f() { return -i; } } public class override_test { public static void main(String args[]) { B b = new B(); A a = (A) b; // Cast b to an instance of class A. System.out.println(a.i); // Now refers to A.i; prints 1; System.out.println(a.f()); // Still refers to B.f(); prints -2; } } I am wondering why a.f() still refers to B.f() while a.i refers to A.i. thanks in advance! 回答1: Simple rule is when you call a