{"id":467,"date":"2021-03-17T01:57:27","date_gmt":"2021-03-17T01:57:27","guid":{"rendered":"https:\/\/phptutorial.net\/?page_id=467"},"modified":"2025-04-06T02:10:32","modified_gmt":"2025-04-06T02:10:32","slug":"php-default-parameters","status":"publish","type":"page","link":"https:\/\/www.phptutorial.net\/php-tutorial\/php-default-parameters\/","title":{"rendered":"PHP Default Parameters"},"content":{"rendered":"\n

Summary<\/strong>: In this tutorial, you’ll learn about PHP default parameters and how to use them to simplify function calls.<\/p>\n\n\n\n

Introduction to the PHP default parameters #<\/a><\/h2>\n\n\n\n

The following defines the concat()<\/code> function that concatenates two strings with a delimiter:<\/p>\n\n\n

<?php<\/span>\n\nfunction<\/span> concat<\/span>($str1, $str2, $delimiter)<\/span>\n<\/span>{\n    return<\/span> $str1 . $delimiter . $str2;\n}<\/span><\/code><\/span>Code language:<\/span> HTML, XML<\/span> (<\/span>xml<\/span>)<\/span><\/small><\/pre>\n\n\n
When you call the concat()<\/code> function, you need to pass exactly three arguments. For example:<\/p>\n\n\n
<?php<\/span>\n\nfunction<\/span> concat<\/span>($str1, $str2, $delimiter)<\/span>\n<\/span>{\n    return<\/span> $str1 . $delimiter . $str2;\n}\n\n$message = concat('Hi'<\/span>, 'there!'<\/span>, ' '<\/span>);\n\necho<\/span> $message;<\/span><\/code><\/span>Code language:<\/span> HTML, XML<\/span> (<\/span>xml<\/span>)<\/span><\/small><\/pre>\n\n\n
However, you’ll find that you often use the space ‘ ‘ as the delimiter. And it’s repetitive to pass the space whenever you call the function.<\/p>\n\n\n\n
This is why default parameters come into play.<\/p>\n\n\n\n
PHP allows you to specify a default argument for a parameter. For example:<\/p>\n\n\n
<?php<\/span>\n\nfunction<\/span> concat<\/span>($str1, $str2, $delimiter = ' '<\/span>)<\/span>\n<\/span>{\n    return<\/span> $str1 . $delimiter . $str2;\n}<\/span><\/code><\/span>Code language:<\/span> HTML, XML<\/span> (<\/span>xml<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, the $delimiter<\/code> parameter takes the space as the default argument.<\/p>\n\n\n\n
When you call the concat()<\/code> function and don’t pass the delimiter argument, the function will use the space for the $delimiter<\/code> like this:<\/p>\n\n\n
<?php<\/span>\n\nfunction<\/span> concat<\/span>($str1, $str2, $delimiter = ' '<\/span>)<\/span>\n<\/span>{\n    return<\/span> $str1 . $delimiter . $str2;\n}\n\n$message = concat('Hi'<\/span>, 'there!'<\/span>);\n\necho<\/span> $message;<\/span><\/code><\/span>Code language:<\/span> HTML, XML<\/span> (<\/span>xml<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Hi there<\/code><\/span><\/pre>\n\n\n
However, if you pass an argument for the $delimiter<\/code>, the function will use that argument instead:<\/p>\n\n\n
<?php<\/span>\n\nfunction<\/span> concat<\/span>($str1, $str2, $delimiter = ' '<\/span>)<\/span>\n<\/span>{\n    return<\/span> $str1 . $delimiter . $str2;\n}\n\n$message = concat('Hi'<\/span>, 'there!'<\/span>, ','<\/span>);\n\necho<\/span> $message;<\/span><\/code><\/span>Code language:<\/span> HTML, XML<\/span> (<\/span>xml<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Hi,there!<\/code><\/span><\/pre>\n\n\n
In this example, we passed a comma to the $delimiter<\/code>. The concat()<\/code> function used the comma (,<\/code>) instead of the default argument.<\/p>\n\n\n\n
When you specify a default argument for a parameter, it becomes optional. This means that you can pass a value or skip it.<\/p>\n\n\n\n
Default arguments #<\/a><\/h2>\n\n\n\n
The default arguments must be constant expressions. They cannot be variables<\/a> or function calls.<\/p>\n\n\n\n
PHP allows you to use a scalar value, an array<\/a>, and null<\/code> as the default arguments.<\/p>\n\n\n\n
The order of default parameters #<\/a><\/h2>\n\n\n\n
When you use default parameters, it’s a good practice to place them after the parameters that don’t have default values. Otherwise, you will get unexpected behavior. For example:<\/p>\n\n\n
<?php<\/span>\n\nfunction<\/span> concat<\/span>($delimiter = ' '<\/span>, $str1, $str2)<\/span>\n<\/span>{\n\treturn<\/span> $str1 . $delimiter . $str2;\n}\n\n$message = concat('Hi'<\/span>, 'there!'<\/span>, ','<\/span>);\n\necho<\/span> $message;\n<\/span><\/code><\/span>Code language:<\/span> HTML, XML<\/span> (<\/span>xml<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
there!Hi,<\/code><\/span><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
    \n
  • Use default parameters to simplify the function calls.<\/li>\n\n\n\n
  • Default parameters are optional.<\/li>\n<\/ul>\n
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    Did you find this tutorial useful?<\/div>\n\t\t
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Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n