PHP code used to check whether the extension library or function is available

With the increase of the version, PHP functions become more and more perfect, and more available extension libraries and functions are available. Therefore, we should also consider the compatibility of versions when writing programs, you also need to check whether the extension Library is installed on the server (especially the virtual host. The functions described in this article are actually available in the PHP Manual. However, these functions are independent and difficult to find, so we will introduce them separately for easy reference.
1. get all available modules-get_loaded_extensions this function returns all loaded (available) modules.
Usage:

The code is as follows:

Print_r (get_loaded_extensions ());

2. obtain the available functions of the specified module-get_extension_funcs. This function returns all available functions of the specified module. The input parameter (module name) must be in lowercase.
Usage:

The code is as follows:

Print_r (get_extension_funcs ("gd "));

3. get all defined functions-get_defined_functions this function returns all defined functions, including built-in functions and user-defined functions.
Usage:

The code is as follows:

Function myrow ($ id, $ data ){
Return"$ Id$ Data\ N ";
}
$ Arr = get_defined_functions ();
Print_r ($ arr );

Output:

The code is as follows:

Array
(
[Internal] => Array
(
[0] => zend_version
[1] => func_num_args
[2] => func_get_arg
[3] => func_get_args
[4] => strlen
[5] => strcmp
[6] => strncmp
...
[1, 750] => bcscale
[751] => bccomp
)
[User] => Array
(
[0] => myrow
)
)

$ Arr ["internal"] is a built-in function, and $ arr ["user"] is a user-defined function.
4. check whether the specified function exists-function_exists. This function returns whether the specified function has been defined.
Usage:

The code is as follows:

If (function_exists ('imap _ open ')){
Echo "IMAP functions are available.
\ N ";
} Else {
Echo "IMAP functions are not available.
\ N ";
}