PHP中define跟defined的区别
PHP中define和defined的区别
PHP中define和defined的区别
对于初学者会混淆这两个函数
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1.define用来定义一个常量,常量也是全局范围的。不用管作用域就可以在脚本的任何地方访问 常量。一个常量一旦被定义，就不能再改变或者取消定义 如:define("website","www.phperz.com") www.phperz.com为常量website的值。
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2.defined用来检测常量有没有被定义,若常量存在，则返回 true，否则返回 false如： if(defined("website")){ echo "true"; }else{ echo "false"; }
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defineHow to define multi-line macros
Oct 11, 2023 pm 01:24 PM
define defines a multi-line macro by using `\` to divide `do { \ printf("%d\n", x); \ } while (0)` into multiple lines for definition. In a macro definition, the backslash `\` must be the last character of the macro definition and cannot be followed by spaces or comments. When using `\` for line continuation, be careful to keep the code readable and make sure there is a `\` at the end of each line.
Explore the importance and role of define function in PHP
Mar 19, 2024 pm 12:12 PM
The importance and role of the define function in PHP 1. Basic introduction to the define function In PHP, the define function is a key function used to define constants. Constants will not change their values during the running of the program. Constants defined using the define function can be accessed throughout the script and are global. 2. The syntax of define function The basic syntax of define function is as follows: define("constant name","constant value&qu
defineHow to define conditional compilation
Oct 11, 2023 pm 01:20 PM
defineConditional compilation can be achieved using the `#ifdef`, `#ifndef`, `#if`, `#elif`, `#else` and `#endif` preprocessing directives.
define usage of function macro
Oct 11, 2023 pm 12:00 PM
The usage of define function macro: 1. Define a simple calculation macro, "#define SQUARE(x) ((x) * (x))"; 2. Define a macro with multiple parameters, "#define MAX(a , b) ((a) > (b) ? (a) : (b))"; 3. Define macros with complex expressions, "#define ABS(x) ((x) < 0 ? -(x ) : (x))”.
The difference between typedef and define
Sep 26, 2023 am 10:41 AM
The difference between typedef and define lies in type checking, scope, readability, error handling, memory usage, etc. Detailed introduction: 1. Type checking, the type alias defined by typedef is a real type, and type checking will be performed, while the macro defined by define is just a simple text replacement, and type checking will not be performed; 2. Scope, the type alias defined by typedef The scope of is local and only valid within the current scope, while the macro defined by define is global and can be used anywhere; 3. Readability, etc.
Detailed explanation of define usage
Oct 11, 2023 am 11:53 AM
define usage: 1. Define constants; 2. Define function macros: 3. Define conditional compilation; 4. Define multi-line macros.
A brief analysis of the solutions to error reports in PHP defined judgments
Mar 23, 2023 pm 04:35 PM
PHP is a commonly used server-side language and is the development language for many large websites. In the PHP development process, we often use the defined() function to determine whether a constant is defined. However, sometimes when we use the defined() function, we will encounter some error prompts. This article will lead you to solve the problem of PHP defined judgment error reporting.
How to use define to define constants
Oct 11, 2023 am 11:57 AM
Usage of define constants: 1. Define numeric constants, "#define PI value"; 2. Define string constants, "#define GREETING "string""; 3. Define expression constants, "#define MAX(a, b) ((a) > (b) ? (a) : (b))”.
