Introducing some PHP functions to determine variables_PHP Tutorial

While this feature makes programming in PHP very easy, it also has an important drawback: when you need to test the type of a variable, languages ​​that handle typing more loosely can be a bit confusing. Fortunately, the developers of PHP noticed this and included a toolkit of functions specifically for testing variables and finding out which specific character category they belong to - that is, whether they contain characters. String, integer, object or boolean.

The more useful functions in this category are listed below, with descriptions and application examples provided.

empty($var)
This function is used to check whether the variable is empty (no value or zero value). Use this function to check user input, for example, form variables. Ensure they contain valid data.

Copy code The code is as follows:

// returns false
$ var = "hello";
echo empty($var) ? "true" : "false";
// returns true
$var = 0000;
echo empty ($var) ? " true" : "false";
?>

gettype($var)
This function returns the type of the variable. For example, "String", "Integer", "Boolean", "Float", etc. This function is generally used to verify that the variable is of the type you expect before inserting it into a strictly typed database field.

Copy code The code is as follows:

// returns string
$var = " hello";
echo gettype($var);
//returns double
$var = 1000.56;
echo gettype($var);
?>

is_bool($var)
This function tests a variable to see if it contains a boolean value (true/false). Use this function to check if a variable is a Boolean variable.

Copy code The code is as follows:

// returns true
$ var = false;
echo is_bool($var) ? "true" : "false";
?>

is_string($var)
This function tests a variable Whether it is a string variable. Use this function to check whether a variable contains string data.

Copy code The code is as follows:

// returns true
$ var = "exception";
echo is_string($var) ? "true" : "false";
// returns true
$var = "88408";
echo is_string($var) ? "true" : "false";
?>

is_numeric($var)
This function tests a variable to see if it contains a number or a string of numbers (string including a symbol, number and decimal point). Use this function to verify that a variable contains a number before using it in calculations.

Copy code The code is as follows:

// returns true
$ var = "+99.766";
echo is_numeric($var) ? "true" : "false";
// returns false
$var = "b00";
echo is_numeric($var ) ? "true" : "false";
?>

is_array($var)
This function tests a variable to see if it is a PHP related or numerically indexed array . Use this function to check whether a variable is an array before processing it in a loop.

Copy code The code is as follows:

// returns true
$ var = array("tiger", "lion", "zebra");
echo is_array($var) ? "true" : "false";
// returns false
$var = "zebra ";
echo is_array($var) ? "true" : "false";
?>

is_null($var)
This function tests a variable to see if it Whether it is NULL. Use this function to check whether a variable is NULL when evaluating data returned by a SQL query.

Copy code The code is as follows:

// returns false
$ var = "aa";
echo is_null($var) ? "true" : "false";
// returns true
$var = null;
echo is_null($var) ? " true" : "false";
?>

is_object($var)
This function tests a variable to see if it is a PHP object. This function is generally used to test whether a variable is a PHP object before calling a method or accessing a property.

Copy code The code is as follows:

// returns false
$var = "exception";
echo is_object($var) ? "true" : "false";
// returns true
$var = new Exception;
echo is_object($var) ? "true" : "false";
?>

isset($var)
This function tests a variable to see if it has been defined. This function is typically used to test whether a variable is defined when evaluating the results of a form submission.

Copy code The code is as follows:

// returns true
$ var = "yes";
echo isset($var) ? "true" : "false";
// returns false
echo isset($test) ? "true" : "false";
?>

print_r($var)
This function prints the contents of a variable. Use this function to "spy" on a variable, especially when debugging a script.

Copy code The code is as follows:

$var = array("one" , "two", array("red", "green"), new Exception, 467);
print_r($var);
?>

http://www.bkjia.com/PHPjc/325322.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/325322.htmlTechArticleWhile this feature is very easy to program using PHP, it also has an important flaw: when you need to test a When it comes to types of variables, languages ​​that deal with loose types can be a little confusing...