Johnson Lin

Command Line ArgumentsC programs can receive parameters from the command line. For example, running: 1$ ./foo hello world The program foo receives two command line arguments: hello and world. How does the program access these command line arguments? C stores the command line input in an array, which can be accessed through the parameters of the main() function. 1234567#include <stdio.h>int main(int argc, char* argv[]) { for (int i = 0; i < argc; i++) { printf(&quo...

When a data type has only a few possible values, each with its own specific meaning, defining these values as an enum (short for “enumeration”) can enhance code readability. 12345enum colors { RED, GREEN, BLUE };printf("%d\n", RED); // 0printf("%d\n", GREEN); // 1printf("%d\n", BLUE); // 2 In the example above, if a program requires three colors, we can use the enum command to define these colors as a single enumeration type called colors, which cons...

Sometimes, you need a data structure that can represent different data types depending on the situation. For instance, if you use a single structure to represent the quantity of fruit, it may need to be an integer (like 6 apples) at times and a float (like 1.5 kilograms of strawberries) at others. In C, you can use a union to create a flexible data structure. A union can contain various members that share the same memory space, meaning only one member can hold a meaningful value at any given ...

OverviewThe typedef command is used to create an alias for a specific type. 1typedef type name; In this code, type represents the original type, while name is the alias. For example: 1typedef unsigned char BYTE; In this example, typedef creates an alias BYTE for the type unsigned char, allowing you to declare variables using BYTE: 1BYTE c = 'z'; Multiple AliasesYou can use typedef to define multiple aliases at once: 1typedef int antelope, bagel, mushroom; Here, antelope, bagel, and ...

OverviewC doesn’t have a dedicated string type. Instead, strings are treated as arrays of characters (char arrays). For example, the string “Hello” is processed as the array {‘H’, ‘e’, ‘l’, ‘l’, ‘o’}. The compiler allocates a continuous block of memory for the array, with all characters stored in adjacent memory units. C automatically adds a null byte (‘\0’) at the end of the string to indicate its termination. This null character is different from the character ‘0’. The null character has an...

IntroductionAn array is a collection of values of the same type stored in a sequential manner. Arrays are represented by a variable name followed by square brackets, with the number inside the brackets indicating the number of elements in the array. 1int scores[100]; In this example, an array named scores is declared with 100 elements, each of which is of type int. Note: When declaring an array, you must specify its size. Array elements are indexed starting from 0. Thus, in an array scores[10...

OverviewA function is a reusable block of code that can accept different parameters and perform specific tasks. Here’s an example of a function: 123int plus_one(int n) { return n + 1;} This code declares a function named plus_one(). Key Points of Function Declarations: Return Type: Specify the return type at the start of the declaration. In the example, int indicates the function returns an integer. Parameters: Declare the types and names of parameters in parentheses following the...

Pointers are one of the most important and challenging concepts in the C programming language. OverviewWhat is a pointer? In essence, it’s a value representing a memory address, acting as a signpost to a specific location in memory. The asterisk * represents a pointer and is usually placed after the type keyword to indicate what type of value the pointer is referencing. For example, char* is a pointer to a character, and float* is a pointer to a float. 1int* intPtr; The above example declares...

In C, every piece of data has a type that the compiler must understand to properly operate on it. The “type” refers to the shared characteristics of similar data, allowing you to know its properties and operations once its type is known. There are three basic data types: char (character), int (integer), and float (floating-point). More complex types are built from these. Character TypeThe character type represents a single character and is declared with the char keyword. 1char c = 'B...

In C programming, execution is sequential, meaning statements are executed one after the other. To control the flow of execution, developers use flow control structures, primarily conditional and loop statements. if StatementThe if statement is used for conditional execution; it executes a specified statement if the condition is true. Syntax: 1if (expression) statement Here, expression must be true (non-zero) for statement to execute. The condition inside the parentheses must be enclosed in p...

C language includes a wide variety of operators, more than 50 in total, which can be categorized into several types. Arithmetic OperatorsArithmetic operators are used for mathematical operations. The main ones are as follows: +: Unary plus (positive sign) -: Unary minus (negative sign) +: Addition (binary operator) -: Subtraction (binary operator) *: Multiplication /: Division %: Modulus (remainder of division) Unary + and -:The + and - can act as unary operators, requiring onl...

A variable can be understood as the name of a memory location. By using the variable name, you can reference this memory and access the stored value. The value might change, which is why it’s called a variable. If the value remains constant, it’s referred to as a constant. Variable NamesIn C, variable names are considered identifiers, and there are strict rules for naming them: They can only contain letters (both uppercase and lowercase), digits, and underscores (_). They cannot begin with ...

StatementsC code is composed of statements. A statement is a command that the program executes. In C, each statement must end with a semicolon, unless specified otherwise. 1int x = 1; The above is a variable declaration statement, where the integer variable x is declared and assigned a value of 1. Multiple statements can be written on a single line: 1int x; x = 1; Here, two statements are written on one line. Line breaks between statements aren’t required but are often used for readability. A...

HistoryThe C programming language was originally invented as a tool for developing the Unix operating system. In 1969, Ken Thompson and Dennis Ritchie at Bell Labs in the United States developed the Unix operating system. Unix was initially written in assembly language, making it difficult to port to other computers. To address this, they decided to rewrite it in a high-level language. However, existing high-level languages at the time did not meet their needs, so Thompson developed the B lan...

当下，随着互联网技术的发展和普及，用户数据逐渐成为重要的商业资源，企业和组织越来越重视对用户的了解和分析。用户画像作为一种有效的工具，可以帮助企业更好地了解目标用户的特点和需求，进而进行精准的市场定位、产品设计和营销推广等活动。 一、什么是用户画像用户画像（User Profile），指通过数据分析、挖掘和整合，对特定用户群体进行描述和分类的过程。它包括用户的个人信息、兴趣爱好、使用行为、社交网络等多个方面的数据，可以帮助企业或组织更好地了解用户需求和习惯，提供个性化的产品和服务。 二、用户画像的应用场景 市场定位：通过用户画像，企业可以了解目标用户的年龄、性别、地域、收入等基本信息，从而确定产品的定位和目标市场。 产品设计：用户画像可以帮助企业了解用户的需求和使用习惯，提供更符合用户需求的产品和服务。 营销推广：通过用户画像，企业可以根据用户的兴趣爱好、购买行为、社交网络等信息，进行精准的广告投放和营销推广，提高广告的点击率和转化率。 客户服务：用户画像可以帮助企业了解用户的消费习惯和偏好，提供更优质的客户服务和售后支持。 三、用户画像的数据来源 用户行为数据：通过用...

在 Elasticsearch 中，每个文档都有唯一的文档 ID，用于标识该文档在索引中的位置。文档ID是一个重要的概念，了解它的长度限制非常重要。 Elasticsearch 文档 ID 的长度限制是 512 Bytes。这意味着文档 ID 不能超过 512 字节的大小。如果你尝试创建一个超过 512 字节的文档 ID，Elasticsearch 将会返回一个错误。这个限制是为了保证索引的性能和稳定性。 以下通过示例来说明 Elasticsearch 文档 ID 的长度限制。 Elasticsearch 版本：7.1.0API 调用均在 Kibana 开发工具上操作 首先，创建一个名为 test_idx 索引：12345678910111213PUT test_idx { "settings": { "number_of_shards": 1 }, "mappings": { "properties": { "...

ABSTRACTLog processing has become a critical component of the data pipeline for consumer internet companies. We introduce Kafka, a distributed messaging system that we developed for collecting and delivering high volumes of log data with low latency. Our system incorporates ideas from existing log aggregators and messaging systems, and is suitable for both offline and online message consumption. We made quite a few unconventional yet practical design choices in Kafka to make our system effici...