understanding macd

Understanding of fork functions and understanding of fork Functions Header file: # include pid_t fork (void); 1. Create a sub-process and return-1 If the sub-process fails.2. Call once and return twice. The child process PID and 0 are returned respectively in the parent and child processes. Using different return values, you can write different processing branches for the parent and child processes respe

DWZ (1): First understanding of the framework and first understanding of the dwz framework The DWZ rich client framework (jQuery RIAframework) is an open-source Ajax RIA framework developed by Chinese people based on jQuery. The design goal of the DWZ rich client framework is simple and practical, easy to expand, fast development, RIA ideas, and lightweight. The DWZ framework supports HTML extension instead

A deep understanding of Java interfaces and abstract classes, and a deep understanding of java Abstraction For object-oriented programming, abstraction is one of its major features. In Java, OOP abstraction can be embodied in two forms: interfaces and abstract classes. There are too many similarities and differences between the two. Many people think that they can be used in different ways when they are ne

the heap, the right side is the memory representation of the function object, the center is the pointing of the prototype attribute of the function object, and the left side is the object instance created by the function object. The function object points to the pointer of the prototype attribute and writes dog1, dog2, and dog3 correspond to three reference changes of Dog. prototype respectively. They also have a relationship with dog1, dog2, and dog3 in the stack. (Note: Function objects will

:\tmemmove with overlap\n" );printf ( "source:\t\t%s\n", string2 + 4);printf ( "destination:\t%s\n", string2 + ten);Memmove (string2 + ten, string2 + 4, 40);printf ( "result:\t\t%s\n", string2);printf ( "length:\t\t%d characters\n\n" , strlen (string2));printf ( "function:\tmemcpy with overlap\n" );printf ( "source:\t\t%s\n", string1 + 4);printf ( "destination:\t%s\n", string1 + ten);memcpy (string1 + ten, string1 + 4, 40);printf ( "result:\t\t%s\n", string1);printf ( "length:\t\t%d characters\n

Today, a small program, I feel that some of the problems are easy to overlook!This program code is as follows:The result of the program is:I think a lot of small white like me may only start to wonder why the final result is 255! First, we need to know that strlen () is a function that calculates the length of a string, but why is the last string length 255? The defined array A does not have 1000 elements, and the For loop is executed 999 times?For Char, we have to know that the implied end tag

The functionality of the scrapy. Third, data processing flowScrapy 's entire data processing process is controlled by the scrapy engine, which operates mainly in the following ways:The engine opens a domain name, when the spider handles the domain name and lets the spider get the first crawl URL. The engine gets the first URL to crawl from the spider , and then dispatches it as a request in the schedule. The engine gets the page that crawls next from the dispatch.The schedule returns the next

Java polymorphism understanding and java polymorphism understanding Implementation of polymorphism in Java What is polymorphism The following are three necessary conditions for the existence of polymorphism, which require that everyone be able to carry out their dreams! Three necessary conditions for Polymorphism1. There must be inheritance;2. There should be rewriting;3. parent class references to child cl

Understanding of JavaScript scopes and block-level scopes, and understanding of javascript concepts Scope is always the top priority of any programming language, because it controls the visibility and lifecycle of variables and parameters. Here, we first understand two concepts: block-level scope and function scope. What is block-level scope? The statement set in any pair of curly braces ({And}) belongs to

A simple understanding of Java exceptions and a simple understanding of JavaWhat is the essence of Java exceptions? Essentially, a java exception is a java Object (inheriting objects). Like a general java Object, it encapsulates some member variables and operations, we can operate java exception objects as we operate on general java objects (I also tried it specially, but can I use the throw keyword to oper

Servlet's personal understanding, Servlet's personal understanding 1. What is Servlet? 1. servlet is a dynamic web page technology based on Java technology. It runs on the server side and is managed by Servlet containers to generate dynamic content. It is very complicated for jsp (servlet to develop web pages, so now it is generally used for process control. Supplement: jsp: the framework of jsp is HTML. It

Object-oriented Exception Handling: an in-depth understanding of java exception handling mechanism, and an in-depth understanding of Exception Handling What is an exception? An exception is a description of the problem. It encapsulates the problem object;Characteristics of the exception system: all classes and objects in the exception system;Can be throttled, that is, it can be operated by the throw and thr

assigning it a value of undefined (not the string "undefined")Undefined and parameter judgmentLet's look at a simple function: 123456 function bool(val){if(typeof val == ‘undefined‘){return true;}return !!val;} Is there a problem with this function? Yes, because typeof return undefined value there are two possible, one is passed in is undefined, there is no value. 12 alert(bool(undefined));//truealert(bool());//true Obviously, bool (undef

My understanding of the relationship between uml class diagrams and my understanding of uml class diagrams Relationship between uml class diagrams: Generalization is inheritance. An Implementation relationship is a class that implements another interface. Dependency is a class that uses another class. It is a usage relationship. In a service of this class, another class is needed for assistance. An associat

Python development [Article 1]: first understanding of Python and first understanding of python I. python Environment 1. Install Python Windows: 1, download installation package 2 https://www.python.org/downloads/3 2, installation 4 default installation path: C: \ python275 3. Configure environment variables 6. Right-click the computer and choose Properties> advanced system Settings> advanced> environment v

A deep understanding of Java reflection and a deep understanding of java To understand the principles of reflection, you must first understand what type information is. Java allows us to identify the object and class information at runtime, mainly in two ways: one is the traditional RTTI, which assumes that we already know all the types of information during compilation; the other is the reflection mechanis

Deep understanding of JAVA polymorphism principles and deep understanding of java Polymorphism I have always known what polymorphism is, and I often use polymorphism when coding, but I have never really understood what the underlying operating mechanism of polymorphism is like, write it down specially, and make progress together with all of you. I also hope you can guide and correct me. The concept of polym

Python decorator understanding, python decorator understanding 1. Functions of the decorator Add new functions for the decorated object without modifying the source code and calling method of the decorated object Principles: 1. Do not modify the source code of the decorated object2. Do not modify the call method of the decorated object Objectives: Add new features to the decorated object 2. Definition and

A deep understanding of Django's custom filters and a deep understanding of django Preface This article mainly introduces you to the Django custom filter and shares it for your reference. I will not talk much about it below. Let's take a look at the details: Filters and functions Django filters are essentially functions, but there are too many "functions". To show their uniqueness, designers think of a nam

Deep understanding of slicing principles and deep understanding of Slicing A data element is obtained by specifying the subscripts or by specifying the subscript range. This access sequence is called slice. In some cases, it is also called a shard. For details about how slice works, refer to my previous article: How slice works in Python. First, analyze the slice operation from the bottom layer:Internally,