如何在 PHP 中删除字符串中的所有空格

### Answer: Use the PHP str_replace() Function
You can simply use the PHP `str_replace()` function to strip or remove all spaces inside a string.

Let's take a look at the following example to see how it actually works:

```php
<?php
$str = 'This is a simple piece of text.';
$new_str = str_replace(' ', '', $str);
echo $new_str; // Outputs: Thisisasimplepieceoftext.
?>
```
The above example will however only remove spaces. If you want to remove all whitespaces including tabs, newlines, etc. you can use the `preg_replace()` function which perform a regular expression search and replace, as demonstrated in the following example:

```php
<?php
$str = "This is a simple \npiece\tof text.";
$new_str = preg_replace("/\s+/", "", $str);
echo $new_str; // Outputs: Thisisasimplepieceoftext.
?>
```
In the above example `\t` represents the tab character, whereas `\n` represents the newline character.

To learn more about regular expression, see the tutorial on [PHP regular expressions](http://www.bixiaguangnian.com/manual/php7/3997.html "PHP regular expressions").