syntax

问题 Is there a syntax trick to get to the constant in a generic class without specifying an (ad-hoc) type? public class MyClass<T>{ public const string MyConstant = "fortytwo"; } // I try to avoid this type specification. var doeswork = MyClass<object>.MyConstant; // Syntax similar to what I'd like to accomplish. var doesnotwork = MyClass.MyConstant; There is a caveat about the static variable (constant) not being shared between different types like MyClass<object> and MyClass<int> but my

问题 I'm trying to create instance of StreamWriter with UTF8 encoding in PowerShell. $f = New-Object System.IO.StreamWriter "a.txt", $false, [System.Text.Encoding]::UTF8 This throws error: New-Object : Cannot find an overload for "StreamWriter" and the argument count: "3". I'm trying to invoke this constructor: https://msdn.microsoft.com/en-us/library/f5f5x7kt(v=vs.110).aspx 回答1: Still, I would like to know what is wrong with my original syntax. Your original syntax (fundamentally correctly) uses

问题 In assmebly the square brackets seem to have the same meaning as * in C. They are used to dereference a pointer. Dereferencing a pointer means going to refer to a specific memory location to read or write it. So it is quite logical to use square brackets in the case of a MOV. But what is the logical reason why they also use it for LEA. LEA EAX, [EBP -4], looks like dereferencing a pointer, ebp - 4, to refer to the pointed memory location but it will not read the value contained in the

问题 In some programming languages, I see (ex.): x := y What is this := operator generally called and what does it do? 回答1: In all languages that support an operator := it means assignment. In languages that support an operator := , the = operator usually means an equality comparison. In languages where = means assignment, == is typically used for equality comparison. does := mean = ? I can't recall any languages where := means the same as = . In MySQL := and = are both used for assignment,

问题 So I have been rattling my brain about using the MutationObserver and I haven't made any progress. I've read about it on the W3C site and in the MDN. When reading it in the MDN, everything made sense until the example. // select the target node var target = document.querySelector('#some-id'); // create an observer instance var observer = new MutationObserver(function(mutations) { mutations.forEach(function(mutation) { console.log(mutation.type); }); }); // configuration of the observer: var

问题 So I have been rattling my brain about using the MutationObserver and I haven't made any progress. I've read about it on the W3C site and in the MDN. When reading it in the MDN, everything made sense until the example. // select the target node var target = document.querySelector('#some-id'); // create an observer instance var observer = new MutationObserver(function(mutations) { mutations.forEach(function(mutation) { console.log(mutation.type); }); }); // configuration of the observer: var

问题 I had declared a Boolean variable bool abc; in a class and thought that it would be false by default. An if condition in my program, if (abc) , turned out to be true, so I output the value of abc, and saw that it contained the value 55. Is this normal? Do we always have to assign 'bool abc=false' to be sure that it is false? 回答1: Yes, you should always initialize your variables. Until you intimately learn the times when it is and isn't necessary to do so explicitly, you should do it all the

问题 I had declared a Boolean variable bool abc; in a class and thought that it would be false by default. An if condition in my program, if (abc) , turned out to be true, so I output the value of abc, and saw that it contained the value 55. Is this normal? Do we always have to assign 'bool abc=false' to be sure that it is false? 回答1: Yes, you should always initialize your variables. Until you intimately learn the times when it is and isn't necessary to do so explicitly, you should do it all the

问题 Hey guys i'm working through a book and i'm little baffled with the sub objective of the following question.. Powers of numbers can be calculated by multiplying the number by itself for as many times as the value of the exponent. For example, 2 raised to the power 4 can be calculated by multiplying 2 by itself 4 times to get 16. Write a program that: 1. inputs a double as the base number and an int as the exponent; double base, ans = 0; int exponent; cout << "This program will calculate the

问题 I've seen this in some JavaScript code but I don't get what it does. for(;;){ //other code } I'm used to the for(i=0;i<someLength;i++){...} format but I'm stuck to figure out how or what the "(;;)" syntax is for? 回答1: In JavaScript, for (;;) { ... } just creates an infinite endless loop, which is almost exactly the same as: while (true) { // ... } or do { // ... } while (true); 回答2: for (;;) is the exact same syntax. You're allowed to leave out parts that go between the semicolons, even all