operators

问题 This question already has answers here : Why does this Java code with “+ +” compile? (8 answers) Closed 5 years ago . So, I expect this not to compile, and it doesn't: // the two is inc'd, so reduces symbolically to println(int int) // which is a compile error System.out.println(1 ++ 2); But this does: System.out.println(1 + + 2); // returns three What gives? Shouldn't it also not compile? Also, this question is very hard to search for because of the operators.. 回答1: Java is interpreting the

问题 What does the & symbol mean in Objective-C? I am currently looking at data constucts and am getting really confused by it. I have looked around the web for it but have not found an answer at all. I know this is possibly a basic Objective-C concept, but I just can't get my head around it. For example: int *pIntData = (int *)&incomingPacket[0]; What is the code doing with incoming packet here? 回答1: & is the C address-of unary operator. It returns the memory address of its operand. In your

问题 For some reason I can't find the answer to this anywhere. I tried Googling "Haskell equal sign arrow" and I'm not getting any results. Let's say we have the following function: sendMessage :: MonadM e m => Message -> m () sendMessage message = do mClient <- getMessageClient liftIO $ send mClient message Where exactly are e and m getting used? Are they being passed into the Message object (function?) and then outputted as a single type, m ()? I don't think it helps that I'm very new to Haskell

问题 I'm used to the and and or keywords in C++. I've always used them and typing them is fast and comfortable for me. Once I've heard that these aliases are non-standard and may not work on all compilers. But I'm not sure of it, I don't really know if it's true. Let's assume that I give someone my code, will he have problems compiling it? Is it all right when I use and , or instead of && , || ? Or are these keywords really non-standard? P.S.I use the MinGW compiler. 回答1: They are in fact standard

问题 What is the difference between the !== operator and the != operator. Does it behave similar to the === operator where it compares both value and the type? 回答1: Yes, it's the same operator like === , just for in equality: !== - returns true if the two operands are not identical. This operator will not convert the operands types, and only returns false if they are the same type and value. —Wikibooks 回答2: Yes, !== is the strict version of the != operator, no type coercion is done if the operands

问题 What is the difference between the !== operator and the != operator. Does it behave similar to the === operator where it compares both value and the type? 回答1: Yes, it's the same operator like === , just for in equality: !== - returns true if the two operands are not identical. This operator will not convert the operands types, and only returns false if they are the same type and value. —Wikibooks 回答2: Yes, !== is the strict version of the != operator, no type coercion is done if the operands

问题 I think if I understand correctly, a <> b is the exact same thing functionally as a != b , and in Python not a == b , but is there reason to use <> over the other versions? I know a common mistake for Python newcomers is to think that not a is b is the same as a != b or not a == b . Do similar misconceptions occur with <> , or is it exactly the same functionally? Does it cost more in memory, processor, etc. 回答1: <> in Python 2 is an exact synonym for != -- no reason to use it, no

问题 It seems that these two operators are pretty much the same - is there a difference? When should I use = and when == ? 回答1: You must use == in numeric comparisons in (( ... )) : $ if (( 3 == 3 )); then echo "yes"; fi yes $ if (( 3 = 3 )); then echo "yes"; fi bash: ((: 3 = 3 : attempted assignment to non-variable (error token is "= 3 ") You may use either for string comparisons in [[ ... ]] or [ ... ] or test : $ if [[ 3 == 3 ]]; then echo "yes"; fi yes $ if [[ 3 = 3 ]]; then echo "yes"; fi yes

问题 I am checking whether a CString variable contains only] Chinese characters. The Unicode range for Chinese characters is 4E00 - 9FFF. I am doing as follows: CString str; char ch; GetDlgItemText( IDC_EDIT1, str ); for(int i=0;i<str.GetLength();i++) { ch=str[i]; if(ch>='\u4E00'&&ch<='\u9FFF') { //even if input chinese character here 'if' evaluates to false SetDlgItemText( IDC_RICHEDIT21, str ); SendDlgItemMessage( IDC_RICHEDIT21, EM_REPLACESEL, TRUE, (LPARAM)(LPCTSTR)str); } else break; But if I

问题 Hey everyone, I am working on parsing the PDF content stream to be able to read and handle annotation operators and also to add these. Can anyone shed some light on how to go about doing this, without using a prebuilt library? I understand it is a daunting exercise, but any pointers would be appreciated. Note: I've read a fair amount of the PDF Reference from Adobe, and mostly understand the concept of the file being an object tree, yet I don't understand how to go about figuring out if an