PHP determines whether constants, variables and functions exist_PHP tutorial

To detect constants, use defined, and to define constants, use define. Note that the constants to be detected need to use quotation marks (either single or double), such as:

The code is as follows

if (defined('CONST_NAME')) {
//do something
}

Variable detection uses isset. Note that if the variable is not declared or is assigned a value of NULL when declared, isset returns FALSE, such as:

The code is as follows

if (isset($var_name)) {
//do something
}

Use function_exists for function detection. Note that the function name to be detected also needs to use quotation marks, such as:

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

Without further ado, let’s look at an example

The code is as follows

/* Determine whether the constant exists*/
if (defined('MYCONSTANT')) {
echo MYCONSTANT;
}
//Determine whether the variable exists
if (isset($myvar)) {
echo "Variable $myvar.";
}
//Determine whether the function exists
if (function_exists('imap_open')) {
echo "Function imag_openn exists";
} else {
echo "Function imag_open does not exist";
}
?>

function_exists determines whether the function exists

The code is as follows

if (function_exists('test_func')) {
echo "Function test_func exists";
} else {
echo "Function test_func does not exist";
}
?>

filter_has_var function

The filter_has_var() function checks whether a variable of the specified input type exists.

If successful, return true, otherwise return false.

The code is as follows

if(!filter_has_var(INPUT_GET, "name"))
{
echo("Input type does not exist");
}
else
{
echo("Input type exists");
}
?>

The output is. Input type exists

http://www.bkjia.com/PHPjc/371412.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/371412.htmlTechArticleUse defined for constant detection, and define for defining constants. Note that the constant to be detected needs to be quoted (either single or double), for example: The code is as follows if (defined('CONST_NAME')) { //do somethin...