问题 #include <stdio.h> #include <string.h> int main() { char greeting[]="\nHello World!\n"; int a; for(int i=0; i<strlen(greeting); i++) greeting[i]^=111; for(int i=0; i<strlen(greeting); i++) greeting[i]^=111; printf("%s\n",greeting); scanf("%d",&a); } Output: Hell Why does it cut everything after spotting a letter corresponding to the XOR key's number (in this case, ASCII 'w')? In mathematical logic, N^N=0 and 0^N=N , doesn't it? 回答1: Because 'o' is ASCII code 111, and XORing 111 with 111

问题 I just installed django and after installing that I created a django project and was trying to run django server by command: python manage.py runserver After that I'am getting error as: SyntaxError: Generator expression must be parenthesized 回答1: TL; DR Update Django to the latest revision. This error is a known incompatibility related to Python issue #32012. Projects based on Django 1.11.16 and below will raise this exception when started with Python 3.7. A patch for this issue has been

问题 This question already has answers here : Closed 9 years ago . Possible Duplicate: How do Trigonometric functions work? What actually goes into the computation of trig functions like Sin, Cos, Tan and Atan? I think I've found an optimization in my code where I can avoid using any of these functions and base the problem around slope instead of angles. So that means a couple division operations in place of the above trig functions. But I'd like to know more about what goes into those trig

问题 Specifically for C and C++, how many passes are used by default? Does this number change depending on the level of optimization used? (it should) Can it be changed directly? I was searching for this information in http://gcc.gnu.org/, but googling using site:http://gcc.gnu.org/ did not yield anything. Any pointers to any documentation about this will also be helpful. By pass I meant a pass over the original representation of the source code only and not the multiple pass definition suggested

问题 I receive a MySQL error when I create a table: SQLSTATE[42000]: Syntax error or access violation: 1059 Identifier name 'FK_SALES_FLAT_CREDITMEMO_GRID_ARCHIVE_STORE_ID_CORE_STORE_STORE_ID' is too long How can the default Identifier name size be increased or how can I solve this otherwise? 回答1: Please take a look at http://dev.mysql.com/doc/refman/5.5/en/identifiers.html - you are limited to 64 chars to an identifier. 回答2: Provide your own shot name to key. $table->unique(['product_id',

问题 I am new to angular and I have the following situation which is I have a service getAnswers():Observable<AnswerBase<any>[]> and two components that are related to each other. online-quote dynamic-form online-quote component calls the service getAnswers():Observable<AnswerBase<any>[]> in its ngOnInit() method and the result of this, is passed to the component dynamic-form . To illustrate the situation this is the code of my two components: online-quote.component.html: <div> <app-dynamic-form

问题 For certain of my branches, I cannot get a version control window. So for example, if I go into branch develop , then the window shows; if I go into master it’s gone and there is nothing I can do to bring it back. I try to trick it by going from develop to master. But as soon as I get to master, it is gone again. The problem is relatively new (7 days). It didn’t use to be like that. Any ideas how I might fix it? I usually use the window for easy access to my log of commits 回答1: I got it

问题 I'm trying to get a column total but when i run this query i get the following error. Any advice? SELECT SUM(Size) as total FROM AllDocs Where DirName LIKE 'sites/test/test%' ERROR: Msg 8115, Level 16, State 2, Line 1 Arithmetic overflow error converting expression to data type int. Warning: Null value is eliminated by an aggregate or other SET operation. 回答1: While all your sizes can fit into INT (up to 2^31 - 1 ), their SUM cannot. Cast them into BIGINT : SELECT SUM(CAST(Size AS BIGINT)) as

问题 What I need to do is to determine whether a word consists of letters except certain letters. For example I need to test whether a word consists of the letters from the English alphabet except letters: I, V and X. Currently I have this long regex for the simple task above: Pattern pattern = Pattern.compile("[ABCDEFGHJKLMNOPQRSTUWYZ]+"); Any of you know any shorthand way of excluding certain letters from a Java regex? Thanks. 回答1: You can use the && operator to create a compound character class

问题 I currently use this code in a recipe: template "/var/django/.ssh/id_rsa" do source "id_rsa.erb" owner "django" group "django" variables :key => ssh_key mode 00600 end And here's what id_rsa.erb looks like: <%= @key %> I was wondering if I could avoid having a template, and simply produce the file from the string. Something like this perhaps: file_from_string "/var/django/.ssh/id_rsa" do source ssh_key owner "django" group "django" mode 00600 end 回答1: Use the file resource and specify the