PHP built-in functions
Built-in functions refer to the functions supported by PHP by default. PHP has built-in many standard common processing functions, including string processing, array functions, file processing, session and cookie processing.
Let's take the string processing function as an example. The built-in function str_replace can be used to replace the string. The following example replaces "jobs" with "steven jobs":
$str = 'i am jobs.';
$str = str_replace('jobs', 'steven jobs', $str);
echo $str; //The result is "i am steven jobs"
Other functions are supported by other extensions, such as mysql database processing functions, GD image processing functions, mail processing functions, etc. PHP loads some commonly used extension libraries by default. We can install or load other extension libraries to increase PHP processing. function.