PHP determines whether constants, variables, and functions exist _php techniques

Copy Code code as follows:

if (defined (' Const_name ')) {
Do something
}

Variable detection is the use of isset, note that the variable is not declared or declared when the assignment is Null,isset return false, such as:

Copy Code code as follows:

if (Isset ($var _name)) {
Do something
}

function detection with function_exists, note that the function name to be detected also need to use quotes, such as:

Copy Code code as follows:

if (function_exists (' Fun_name ')) {
Fun_name ();
}

Let's not say much more.

Copy Code code as follows:

<?php
/* To determine whether a constant exists/*
if (defined (' myconstant ')) {
Echo myconstant;
}
To determine whether a variable exists
if (Isset ($myvar)) {
echo "exists variable $myvar."
}
To determine whether a function exists
if (function_exists (' Imap_open ')) {
echo "exists function Imag_openn";
} else {
echo "function Imag_open does not exist n";
}
?>

Function_exists to determine whether a function exists

Copy Code code as follows:

<?php
if (function_exists (' Test_func ')) {
echo "function test_func exist";
} else {
echo "function Test_func does not exist";
}
?>

Filter_has_var function

The Filter_has_var () function checks for the existence of a variable of the specified input type.
If successful, returns TRUE, otherwise returns false.

Copy Code code as follows:

<?php
if (!filter_has_var (Input_get, "name"))
{
Echo ("Input type does not exist");
}
Else
{
Echo ("Input type exists");
}
?>

Output is. Input type exists