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PHP Determines whether constants, variables and functions exist
Determines whether variables are defined: defined()
1 if (defined('CONST_NAME')) { 2 //do something 3 }
Determine whether the variable exists: isset(). Note that the variable is not declared or is assigned a value of NULL when declared. isset returns FALSE, such as:
1 if (isset($var_name)) { 2 //do something 3 }
Function detection Use function_exists, note that the function name to be detected also needs to use quotation marks, such as:
1 if (function_exists('fun_name')) { 2 fun_name(); 3 }
Example:
<?php /* 判断常量是否存在*/ if (defined('MYCONSTANT')) { echo MYCONSTANT; } //判断变量是否存在 if (isset($myvar)) { echo "存在变量$myvar."; } //判断函数是否存在 if (function_exists('imap_open')) { echo "存在函数imag_openn"; } else { echo "函数imag_open不存在n"; } ?>
function_exists determines whether the function exists
1 <?php 2 if (function_exists('test_func')) { 3 echo "函数test_func存在"; 4 } else { 5 echo "函数test_func不存在"; 6 } 7 ?>
filter_has_var function
filter_has_var() function checks whether a variable of the specified input type exists.
If successful, return true, otherwise return false.
1 <?php 2 if(!filter_has_var(INPUT_GET, "name")) 3 { 4 echo("Input type does not exist"); 5 } 6 else 7 { 8 echo("Input type exists"); 9 } 10 ?>
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