Summary of various judgments on strings in php

The content of this article is to share with you a summary of various judgments on strings in PHP. The content is very detailed and has certain reference value. I hope it can help friends in need.

1. Determine whether the string is empty

$namedRange !== NULL$pSheet === NULL

2. Determine whether the file exists and whether it is readable

(file_exists($pClassFilePath) === FALSE) || (is_readable($pClassFilePath) === FALSE)

3. Compare the two "PHP normalized" version number strings

version_compare ( string $version1 , string $version2 [, string $operator ] )

Return mixed string $version1 – version 1 required string $version2 – version 2 required string $operator – understood as Optional operators

are <, lt, <=, le, >, gt, >=, ge, ==, =, eq, !=, <> and ne.

If the third parameter is specified, a boolean is returned. If the third parameter is not specified, the following three situations are returned:

The first version is lower than the second version. Return -1 when the first version is equal to the second version, return 0 when the first version is less than the second version, return 1**Example**version_compare(PHP_VERSION, '5.3.0') >= 0

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