{"id":2269,"date":"2021-07-11T07:43:21","date_gmt":"2021-07-11T07:43:21","guid":{"rendered":"https:\/\/phptutorial.net\/?page_id=2269"},"modified":"2025-04-06T02:50:39","modified_gmt":"2025-04-06T02:50:39","slug":"php-strict_types","status":"publish","type":"page","link":"https:\/\/www.phptutorial.net\/php-tutorial\/php-strict_types\/","title":{"rendered":"PHP strict_types"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to enable strict typing using the PHP strict_types<\/code> directive.<\/p>\n\n\n\n

Introduction to the PHP strict typing #<\/a><\/h2>\n\n\n\n

Type hints<\/a> allow you to declare types for function parameters<\/a> and return values. For example:<\/p>\n\n\n

<?php<\/span>\n\nfunction<\/span> add<\/span>(int $x, int $y)<\/span>\n<\/span>{\n    return<\/span> $x + $y;\n}\n\necho<\/span> add(1.5<\/span>, 2.5<\/span>); \/\/ 3<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, the add()<\/code> function accepts two integers and returns their sum.<\/p>\n\n\n\n
To enable strict typing, you can use the declare(strict_types=1);<\/code> directive at the beginning of the file like this:<\/p>\n\n\n
<?php<\/span>\n\ndeclare<\/span>(strict_types=1<\/span>);\n\nfunction<\/span> add<\/span>(int $x, int $y)<\/span>\n<\/span>{\n    return<\/span> $x + $y;\n}\n\necho<\/span> add(1.5<\/span>, 2.5<\/span>); <\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
By adding the strict typing directive to the file, the code will execute in strict mode. PHP enables the strict mode on a per-file basis.<\/p>\n\n\n\n
In the strict mode, PHP expects the values with the type to match the target types. If there’s a mismatch, PHP will issue an error.<\/p>\n\n\n\n
If you execute the script again, PHP will issue an error as follows:<\/p>\n\n\n
Fatal error: Uncaught TypeError: Argument 1<\/span> passed to add() must be of the type int, float given, called in ...<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Note that you need to place the declare(strict_types=1);<\/code> directive at the beginning of the script file before any other statements.<\/p>\n\n\n\n
PHP strict_types: the special case #<\/a><\/h2>\n\n\n\n
The strict typing directive has a special case when the target type is float<\/code>. If the target type is float<\/code>, you can pass a value of type integer<\/code>. For example:<\/p>\n\n\n
<?php<\/span>\n\ndeclare<\/span>(strict_types=1<\/span>);\n\nfunction<\/span> add<\/span>(float $x, float $y)<\/span>\n<\/span>{\n    return<\/span> $x + $y;\n}\n\necho<\/span> add(1<\/span>, 2<\/span>); \/\/ 3<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
PHP strict_types and include #<\/a><\/h2>\n\n\n\n
Suppose you define the add()<\/code> function in the functions.php<\/code> file:<\/p>\n\n\n
<?php<\/span>\n\ndeclare<\/span>(strict_types=1<\/span>);\n\nfunction<\/span> add<\/span>(int $x, int $y)<\/span>\n<\/span>{\n    return<\/span> $x + $y;\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
<?php<\/span>\n\ninclude<\/span> 'functions.php'<\/span>;\n\necho<\/span> add(1.5<\/span>, 2.5<\/span>);<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Even though the functions.php<\/code> declares the strict typing directive, it does not affect the index.php<\/code>.<\/p>\n\n\n\n
When you call a function defined in a file with strict typing (functions.php) from a file without strict typing (index.php<\/code>), PHP will respect the preference of the caller (index.php<\/code>). That means it’s up to the caller to decide whether to use the strict mode. In this case, the index.php<\/code> won’t execute in the strict mode.<\/p>\n\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
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  • Use the PHP strict_types directive to enable strict typing or strict mode.<\/li>\n\n\n\n
  • In strict mode, PHP accepts only values corresponding to the type declarations and issues a TypeError<\/code> exception if there’s a mismatch.<\/li>\n\n\n\n
  • When you include code from another file, PHP uses the caller’s mode.<\/li>\n<\/ul>\n
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    Did you find this tutorial useful?<\/div>\n\t\t
    \n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t Yes <\/span>\n\t\t\t<\/button>\n\n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t No <\/span>\n\t\t\t<\/button>\n\t\t<\/div>\n\t<\/header>\n\n\t
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Note that the include<\/a><\/code> construct loads the code from another file into a file. And you’ll learn more about it in the later tutorial.<\/p>\n\n\n\n
And you include<\/a> the functions.php<\/code> in the index.php<\/code> file:<\/p>\n\n\n
However, when you pass two floats 1.5 and 2.5, the add()<\/code> function returns 3 because PHP implicitly coerces the values to the target types by default. In this case, PHP coerces the floats<\/a> into integers<\/a>.<\/p>\n\n\n\n