PHP operator and process analysis-PHP Tutorial-php.cn

PHP operator and process analysis

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Release： 2023-03-21 13:56:02

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This article mainly shares with you the analysis of PHP operators and processes, hoping to help everyone have a clearer understanding of PHP operators and processes.

Comparison Operator


Operator 1 Type	Operator 2 Type	Result
null or string	string	Convert NULL to "" for numerical or lexical comparison
bool or null	Any other type	Convert to bool, FALSE
object	object	Built-in classes can define their own comparisons. Different classes cannot be compared. Properties of the same class and arrays are compared in the same way (in PHP 4). PHP 5 has its own instructions
string，resource or number	string,resource or number	Convert strings and resources to numbers, comparing by ordinary math
array	array	has less The array of members is small. If the key in operand 1 does not exist in operand 2, the array cannot be compared, otherwise the values are compared one by one (see the example below)
object	Any other type	object is always larger
array	Any other type	array is always larger

Ternary operator

Expression (expr1) ? (expr2) : (expr3) The value when expr1 evaluates to TRUE is expr2, The value when expr1 evaluates to FALSE is expr3.

Since PHP 5.3, the middle part of the ternary operator can be omitted. The expression expr1 ?: expr3 returns expr1 if expr1 evaluates to TRUE and expr3 otherwise.

Error control operator

PHP supports an error control operator: @. When placed before a PHP expression, any error message that expression may produce is ignored.

If you set a custom error handling function with set_error_handler(), it will still be called, but this error handling function can (and should) call error_reporting(), and this function has @ will return 0.

If activated track_errors feature, any error information generated by the expression is stored in a variable. This variable is overwritten on every error, so check it as early as possible if you want to use it.

<?php
/* Intentional file error */
$my_file = @file (&#39;non_existent_file&#39;) or
    die ("Failed opening file: error was &#39;$php_errormsg&#39;");
// this works for any expression, not just functions:
$value = @$cache[$key];
// will not issue a notice if the index $key doesn&#39;t exist.
?>

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Note: The @ operator is only valid for expressions. A simple rule for beginners is: if you can get a value from somewhere, prepend it with the @ operator. For example, you can put it in variables, functions and include before calls, constants, etc. It cannot be placed before the definition of a function or class, nor can it be used in conditional structures such as if and foreach etc.

include

The included file is first searched according to the path given by the parameter. If no directory (only file name) is given, it is searched according to Search in the directory specified by include_path. If the file is not found under include_path, include will finally search in the directory where the calling script file is located and the current working directory. The include construct emits a warning if the file is not found at the end; this is different from require, which emits a fatal error.

When a file is included, the code contained in it inherits the variable scope of the line where the include is located. From that point on, any variables available in the calling file at that line are also available in the called file. However, all functions and classes defined in include files have global scope.

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