Backend Development
PHP Tutorial
PHP comparison operations and logical operations, php operation logic_PHP tutorial
PHP comparison operations and logical operations, php operation logic_PHP tutorial
PHP comparison operations and logical operations, PHP operation logic
1. The following values are judged to be true using empty():
UnassignedVariable, undeclared variable, 0, "0", "", false, null, empty array array(), object's magic method __get() Returned value
In versions lower than PHP5.0, objects without any attributes are also judged as empty by empty
Note: empty() only accepts variables or index values or attribute values of variables. Constants cannot be passed in directly, nor operation expressions can be passed in. Expressions are supported after PHP 5.5
2. Values judged as false by isset(): unassigned variables, undeclared variables, null, values returned by __get() accept the same participation as empty(), and cannot be constants and expressions.
3. Comparison of different types of data
If one of them is of boolean type or null, convert it to boolean for comparison,
Otherwise, if one is a number, convert it to number and compare ,
Otherwise, if one of them is a string, convert it to string and compare
Object type is always greater than array type and scalar type, array type is always greater than scalar type
Note these comparison results:
<span>//</span><span>0开头的数字字符串转数字时不会按八进制转换，而是简单地丢弃把 '0' 丢弃按数字进行比较，</span>
123=='0123' <span>//</span><span>true</span>
"123"<"0124" <span>//</span><span>true，0开头的数字字符串直接按十进制数字比较而非八进制</span>
"012" == 10 <span>//</span><span> false</span>
012 == 10 <span>//</span><span> true</span>
0x12 == 18 <span>//</span><span> true</span>
"0x12" == 18 <span>//</span><span> true</span>
<span>false</span> < <span>true</span>; <span>//</span><span>true</span>
2><span>true</span>; <span>//</span><span> false</span>
2==<span>true</span>; <span>//</span><span> true </span>
<span>null</span>==0; <span>//</span><span>true</span>
-1<0;<span>//</span><span>true</span>
-1<<span>null</span>;<span>//</span><span>false ,-1 转 bool 是true</span>
4. Type conversion rules
The value judged as true by empty() is converted to boolean type to get false , otherwise, it is true (the value returned by __get() needs to be a specific value Judgment)
The value judged as true by empty() is converted to number and the result is 0. The non-empty array is converted to number and the value is 1 (the value returned by __get() needs to be judged according to the specific value)
<span>class</span><span> Test{
</span><span>private</span> <span>$k</span>=1<span>;
</span><span>public</span> <span>function</span> __get(<span>$propertyName</span><span>){
</span><span>return</span> 123<span>;
}
}
</span><span>$obj</span> = <span>new</span><span> Test();
</span><span>echo</span> json_encode(<span>empty</span>(<span>$obj</span>->k)); <span>//</span><span>true</span>
<span>echo</span> json_encode(<span>isset</span>(<span>$obj</span>->k)); <span>//</span><span>false</span>
<span>echo</span> json_encode((bool)(<span>$obj</span>->k)); <span>//</span><span>true</span>
Several string to number conversion scenarios:
<span>echo</span> 'abc'*1 ; <span>//</span><span>0 </span>
<span>echo</span> '012'*1; <span>//</span><span>12 乘法：可以转换十六进制数，不是数字开头则返回 0</span>
<span>echo</span> '0x12.123'*1; <span>//</span><span>18</span>
<span>echo</span> (<span>float</span>)'0x12' ;<span>//</span><span>0 </span>
<span>echo</span> (int)'0x12' ; <span>//</span><span>0 不能处理十六进制数</span>
<span>echo</span> (<span>float</span>)'12abc'; <span>//</span><span>12 截取左侧字符串</span>
<span>echo</span> (<span>float</span>)'abc'; <span>//</span><span> 0 不是数字返回0</span>
<span>is_numeric</span>('0x123'); <span>//</span><span>true 能识别十六进制数</span>
<span>is_numeric</span>('0x123.123'); <span>//</span><span>false 识别目标是整个字符串而非截取前面一部分</span>
When converting string to number, intercept the numeric string on the left for conversion. If there is no string, return 0.
Convert other data to string:
<span>//几个转字符串的值</span>
(<span>string</span>)0 ; <span>//</span><span> "0"</span> (<span>string</span>)<span>true</span>; <span>//</span><span> "1"</span> (<span>string</span>)<span>false</span>; <span>//</span><span> ""</span> (<span>string</span>)<span>null</span>; <span>//</span><span> ""</span> (<span>string</span>)<span>array</span>(); <span>//</span><span> "<span>Array</span>"</span>
Arrays can be directly concatenated with strings but cannot be subjected to mathematical operations.
Converting the object type to boolean is always true. The object type cannot be converted to number and string, so string splicing and mathematical operations cannot be performed
The way to convert a scalar into an array is to set the first element of the array to a scalar and return the array.
The scalar is converted to object to get an instance of the stdClass class. The value of the scalar is assigned to the attribute named scalar: Object( [scalar] => 234)
Convert array to object to get an instance of stdClass class. The key of the array is the property name of the class.
Object to array conversion is a bit complicated:
Methods, static properties, and class constants are discarded
The protected attribute name is preceded by a "*"
Private attributes are prefixed with the class name (the case is exactly the same as the class name)
Add space characters before and after these prefixes For example, an array converted from object is:
<span>Array</span>( [*v] => 444 [bf] => 333 [bk] => 99977 [Ak] => 999 [*p] => 888 [a2] => 22)
The original objects include:
Public attribute a2, protected attribute v, p, which class these attributes come from cannot be identified (if overridden, the attributes of the subclass will be taken)
来自类 b 的 private 属性 f、k，(从数组 key 来看，以bf为例，无法判断他是属性名为bf，还是来自类b的私有属性f)
来自类 A 的 private 属性 k
无法鉴别 b 和 A 哪个是子类哪个是父类(仅从 array 的key来看，也无法推断出原对象构造自哪个类)
例子：
<span>class</span><span> A {
</span><span>private</span> <span>$A</span> = 'private property, $A of class A'; <span>//</span><span> This will become '\0A\0A'</span>
<span>protected</span> <span>$C</span> = 'protected property, $C of class A'<span>;
}
</span><span>class</span> B <span>extends</span><span> A {
</span><span>private</span> <span>$A</span> = 'private property, $A of class B'; <span>//</span><span> This will become '\0B\0A'</span>
<span>public</span> <span>$AA</span> = 'public property, $AA of class B'; <span>//</span><span> This will become 'AA'</span>
<span>protected</span> <span>$B</span> = 'protected property, $B of class B'<span>;
}
</span><span>$arr</span> = (<span>array</span>) <span>new</span><span> B();
</span><span>foreach</span> (<span>$arr</span> <span>as</span> <span>$key</span> => <span>$value</span><span>) {
</span><span>echo</span> '<br />'<span>;
</span><span>echo</span> <span>$key</span> .',length: '.<span>strlen</span>(<span>$key</span>).' value: '.<span>$value</span><span>;
}</span>
输出结果：
BA,length: 4 value: <span>private</span> property, <span>$A</span> of <span>class</span><span> B AA</span>,length: 2 value: <span>public</span> property, <span>$AA</span> of <span>class</span><span> B </span>*B,length: 4 value: <span>protected</span> property, <span>$B</span> of <span>class</span><span> B AA</span>,length: 4 value: <span>private</span> property, <span>$A</span> of <span>class</span><span> A </span>*C,length: 4 value: <span>protected</span> property, <span>$C</span> of <span>class</span> A
5、 逻辑运算总是返回 true 或 false (写多了 javascript 的人要注意),逻辑运算符优先级从高到低 为 &&、 ||、 and、 or ，逻辑运算符的短路效果可以使用语句中，但记住他们不会像 javascript 中那样返回一个 不是 boolean 类型的值，在表达式中使用要注意。
<span>$a</span> = 1<span>; </span><span>$b</span>=0<span>; </span><span>$b</span> and <span>$a</span> = 100<span>; </span><span>echo</span> <span>$a</span>; <span>//</span><span>1</span> <span>$b</span> || <span>$a</span> = 200<span>; </span><span>echo</span> <span>$a</span>; <span>//</span><span>200</span>
6、switch 的比较不是 "===" 而是 "==" (在 javascript 中是 "===")
7、 在 php4 中，object 之间的比较方式与 array 相同，在 php5 中 , object 类型间的 "==" 比较为 true的前 提是，他们属于同一个类的实例(当然还要进行属性的比较，这类似标量的"==="比较)，object 间的 "===" 比较为 true 的前提是他 们 就是同一个对象。
在 PHP4 中 ，不包括任何成员变量的对象 被 empty() 判断为 true
字符串偏移 offset 取字符的 empty() 判定： 取对应 offset 的字符进行判断，在PHP5.4 以前，使用索引从字符串中取字符时会先将索引进行取整，因此左侧不包含数字的字符串都被转换成0，PHP5.4之后，不再对非整形格式的字符串索引进行取整，因此判断为 true, 同理，isset() 判定为false. 如：
<span>$str</span> = 'ab0d'<span>; </span><span>empty</span>(<span>$str</span>[0]); <span>//</span><span>false</span> <span>empty</span>(<span>$str</span>[0.5]); <span>//</span><span>false 索引被向下取整 为 0</span> <span>empty</span>(<span>$str</span>["0.5"]); <span>//</span><span>false 索引被向下取整 为 0，PHP5.4之后不取证，判定为 true </span> <span>empty</span>(<span>$str</span>[2]); <span>//</span><span>true ，取得的字符为 "0"</span> <span>empty</span>(<span>$str</span>["3"]); <span>//</span><span>false ，取得的字符为 "d"</span> <span>empty</span>(<span>$str</span>[4]); <span>//</span><span>true ,索引超出范围,notice 警告，但 empty() 会忽略警告</span> <span>empty</span>(<span>$str</span>['a']); <span>//</span><span> false ,左侧不包含数字字符串索引 PHP5.4之前被处理为 $str[0]，PHP5.4之后，直接为判定 true </span>
无论是“不等于”还是”==“ ，不要在 PHP 的跨类型数据比较中使用”传递性“：
$a == $b; //true
$b == $c; //true
并不能说明 $a == $c 为 true
数组的比较方法
<span>//</span><span> 数组是用标准比较运算符这样比较的</span>
<span>function</span> standard_array_compare(<span>$op1</span>, <span>$op2</span><span>)
{
</span><span>if</span> (<span>count</span>(<span>$op1</span>) < <span>count</span>(<span>$op2</span><span>)) {
</span><span>return</span> -1; <span>//</span><span> $op1 < $op2</span>
} <span>elseif</span> (<span>count</span>(<span>$op1</span>) > <span>count</span>(<span>$op2</span><span>)) {
</span><span>return</span> 1; <span>//</span><span> $op1 > $op2</span>
<span> }
</span><span>foreach</span> (<span>$op1</span> <span>as</span> <span>$key</span> => <span>$val</span><span>) {
</span><span>if</span> (!<span>array_key_exists</span>(<span>$key</span>, <span>$op2</span><span>)) {
</span><span>return</span> <span>null</span>; <span>//</span><span> uncomparable</span>
} <span>elseif</span> (<span>$val</span> < <span>$op2</span>[<span>$key</span><span>]) {
</span><span>return</span> -1<span>;
} </span><span>elseif</span> (<span>$val</span> > <span>$op2</span>[<span>$key</span><span>]) {
</span><span>return</span> 1<span>;
}
}
</span><span>return</span> 0; <span>//</span><span> $op1 == $op2</span>
}
8、三元运算符 ?: ，跟其他大多数编程语言不一样，PHP 的三元运算符是左结合的！
<span>$arg</span> = 'T'<span>;
</span><span>$vehicle</span> = ( ( <span>$arg</span> == 'B' ) ? 'bus' :<span>
( </span><span>$arg</span> == 'A' ) ? 'airplane' :<span>
( </span><span>$arg</span> == 'T' ) ? 'train' :<span>
( </span><span>$arg</span> == 'C' ) ? 'car' :<span>
( </span><span>$arg</span> == 'H' ) ? 'horse' :
'feet'<span> );
</span><span>echo</span> <span>$vehicle</span>; <span>//</span><span>horse</span>
三元运算表达式被划分为
( <span>$arg</span> == 'B' ) ? 'bus' : ( <span>$arg</span> == 'A'<span> )
</span>? 'airplane' : ( <span>$arg</span> == 'T'<span> )
</span>? 'train' : ( <span>$arg</span> == 'C'<span> )
</span>? 'car' : ( <span>$arg</span> == 'H'<span> )
</span>? 'horse' : 'feet' ; 
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
1664
14
1423
52
1321
25
1269
29
1249
24
PHP and Python: Comparing Two Popular Programming Languages
Apr 14, 2025 am 12:13 AM
PHP and Python each have their own advantages, and choose according to project requirements. 1.PHP is suitable for web development, especially for rapid development and maintenance of websites. 2. Python is suitable for data science, machine learning and artificial intelligence, with concise syntax and suitable for beginners.
PHP in Action: Real-World Examples and Applications
Apr 14, 2025 am 12:19 AM
PHP is widely used in e-commerce, content management systems and API development. 1) E-commerce: used for shopping cart function and payment processing. 2) Content management system: used for dynamic content generation and user management. 3) API development: used for RESTful API development and API security. Through performance optimization and best practices, the efficiency and maintainability of PHP applications are improved.
PHP: A Key Language for Web Development
Apr 13, 2025 am 12:08 AM
PHP is a scripting language widely used on the server side, especially suitable for web development. 1.PHP can embed HTML, process HTTP requests and responses, and supports a variety of databases. 2.PHP is used to generate dynamic web content, process form data, access databases, etc., with strong community support and open source resources. 3. PHP is an interpreted language, and the execution process includes lexical analysis, grammatical analysis, compilation and execution. 4.PHP can be combined with MySQL for advanced applications such as user registration systems. 5. When debugging PHP, you can use functions such as error_reporting() and var_dump(). 6. Optimize PHP code to use caching mechanisms, optimize database queries and use built-in functions. 7
The Enduring Relevance of PHP: Is It Still Alive?
Apr 14, 2025 am 12:12 AM
PHP is still dynamic and still occupies an important position in the field of modern programming. 1) PHP's simplicity and powerful community support make it widely used in web development; 2) Its flexibility and stability make it outstanding in handling web forms, database operations and file processing; 3) PHP is constantly evolving and optimizing, suitable for beginners and experienced developers.
PHP vs. Python: Understanding the Differences
Apr 11, 2025 am 12:15 AM
PHP and Python each have their own advantages, and the choice should be based on project requirements. 1.PHP is suitable for web development, with simple syntax and high execution efficiency. 2. Python is suitable for data science and machine learning, with concise syntax and rich libraries.
PHP and Python: Code Examples and Comparison
Apr 15, 2025 am 12:07 AM
PHP and Python have their own advantages and disadvantages, and the choice depends on project needs and personal preferences. 1.PHP is suitable for rapid development and maintenance of large-scale web applications. 2. Python dominates the field of data science and machine learning.
PHP vs. Other Languages: A Comparison
Apr 13, 2025 am 12:19 AM
PHP is suitable for web development, especially in rapid development and processing dynamic content, but is not good at data science and enterprise-level applications. Compared with Python, PHP has more advantages in web development, but is not as good as Python in the field of data science; compared with Java, PHP performs worse in enterprise-level applications, but is more flexible in web development; compared with JavaScript, PHP is more concise in back-end development, but is not as good as JavaScript in front-end development.
PHP and Python: Different Paradigms Explained
Apr 18, 2025 am 12:26 AM
PHP is mainly procedural programming, but also supports object-oriented programming (OOP); Python supports a variety of paradigms, including OOP, functional and procedural programming. PHP is suitable for web development, and Python is suitable for a variety of applications such as data analysis and machine learning.
