for-loop

问题 In general (or from your experience), is there difference in performance between for and while loops? What if they are doubly/triply nested? Is vectorization (SSE) affected by loop variant in g++ or Intel compilers? Thank you 回答1: Here is a nice paper on the subject. 回答2: Any intelligent compiler won't really show a difference between them. A for loop is really just syntactic sugar for a certain form of while loop, anyways. 回答3: This is something easily ascertained by looking at disassembly.

问题 I frequently write for-loops in bash with the well-known syntax: for i in {1..10} [...] Now, I'm trying to write one where the top is defined by a variable: TOP=10 for i in {1..$TOP} [...] I've tried a variety of parens, curly-brackets, evaluations, etc, and typically get back an error "bad substitution". How can I write my for-loop so that the limit depends on a variable instead of a hard-coded value? 回答1: You can use for loop like this to iterate with a variable $TOP : for ((i=1; i<=$TOP; i

问题 This question already has an answer here : Does a C++11 range-based for loop condition get evaluated every cycle? (1 answer) Closed 6 years ago . Given this C++11 example code: for ( const auto &foo : bar() ) { // ... do something with foo... } Is it guaranteed by the standard that the expression bar() in this example is evaluated only once? Or could it end up being called at every iteration of the loop? 回答1: It is evaluated only once. The standard says that the range-based for loop is

问题 I feel like I'm going around in circles with FOR loop options. I'm trying to take a string (output of a command) and split it on commas, then use each value to SET, e.g. String: USER=Andy,IP=1.2.3.4,HOSTNAME=foobar,PORT=1234 So I want to split on comma and then literally use that variable in SET. I don't know ahead of time how many many variables there will be. I've tried things like: FOR %%L IN (%MYSTRING%) DO ECHO %%L but that splits on the equals sign too so I end up with USER Andy IP 1.2

问题 I am trying to make a christmas tree using for loops and nested for loops. For me to do that I need to be able to make a pyramids with *. I have tried countless times and I am having problems making one. Here is my code: for(int i=1;i<=10;i++){ for(int j=10;j>i;j--){ System.out.println(" "); } for(int k=1;k<=i;k++){ System.out.print("*"); } for(int l=10;l<=1;l++){ for(int h=1;h<=10;h++){ System.out.print(" "); } } System.out.println(); } What I am trying to do is: * *** ***** ******* 回答1: Try

问题 I know the meaning of foreach in programming and when to use it. Is there a foreach keyword in Java? I tried to find a list of keywords but there is only for and not foreach . 回答1: foreach is not a java keyword (IDE recognizes it and puts the "For-each" loop). 回答2: To my knowledge, Java does not have a foreach keyword (unlike C# if I am not mistaken). You can however, iterate over all the elements in an Iterable collection using a modified version of the for loop: List<String> list = new

问题 I have a simple question, i have following simple Parallel for loop. this for loop is part of windows service. I want to stop the loop, when someone stops the service. I can find three ways to stop parallel for, which is in if condition. What is the best way of stopping the parallel for loop and what are the differences? CancellationTokenSource cancellationToken = new CancellationTokenSource(); ParallelOptions options = new ParallelOptions(); options.CancellationToken = cancellationToken

问题 The thing I really hate when learning a new language / framework is how ignorant I feel when I get stuck on a seemingly easy to solve issue. I have a django for loop inside a html page but for some reason it is not working. I have missed something and cannot fix the issue on my own, so I turn to StackOverflow to help me. This is my model I am running my query on models.py : class RIAchievement(models.Model): riAchievementID = models.AutoField(primary_key=True, db_column="RIAchievementID")

问题 This question mentioned the obvious, idiomatic usage of C++11 range-based for. for (auto& elem: container) { // do something with elem } I've been having doubts about the kind of reference you're supposed to use, though. Input iterators may return rvalues. Although the implicit type introduced by auto could be deduced to const which would bind to an rvalue, that doesn't seem to occur. Is the best general practice to use perfect forwarding? for (auto && elem: container) { // do something with

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 5 years ago . I am working on getting the performance parameters of a tcp connection and one these parameters is the bandwidth. I am intending to use the tcp_info structure supported from linux 2.6 onwards, which holds the meta data about a tcp connection. The information can be retrieved using the getsockopt() function call