PHP Notes: Usage Analysis of Data Types and Constants_PHP Tutorial

setType — Set the type of variable

bool settype ( mixed $var , string $type )
Set the type of variable var to type .

Possible values ​​for

type are:

• "boolean" (or "bool" since PHP 4.2.0)
• "integer" (or "int" since PHP 4.2.0)
• "float" ( Only available after PHP 4.2.0, "double" used in older versions is now deprecated)
•"string"
•"array"
•"object"
•" null" (since PHP 4.2.0)

Returns TRUE if successful, FALSE if failed.

intval(), floatval(), stringval() will not change the type of the original variable.

isset—Detect whether the variable is set

bool isset ( mixed $var [, mixed $var [, $... ]] )

Returns TRUE if var exists, otherwise returns FALSE.

If a variable has been released using unset(), it will no longer be isset(). If you use isset() to test a variable that is set to NULL, it will return FALSE. Also note that a NULL byte ("

Note: Warning isset() can only be used with variables, as passing any other parameters will cause a parsing error. If you want to check whether a constant has been set, use the defined() function.

empty — Checks if a variable is empty

bool empty ( mixed $var )

If var is a non-empty or non-zero value, empty() returns FALSE. In other words, "", 0, "0", NULL, FALSE, array(), var $var; and objects without any attributes will be considered empty. If var is empty, TRUE is returned. When the variable No warning will be generated if no value is set.

unset — Unset the given variable

void unset ( mixed $var [, mixed $var [, $... ]] )

unset() destroys the specified variable. Note that in PHP 3, unset() will return TRUE (actually the integer value 1), while in PHP 4, unset() is no longer a real function: it is now a statement. There is no return value, and trying to get the return value of unset() will result in a parsing error.

gettype — Get the type of a variable

string gettype ( mixed $var )

Returns the type of PHP variable var .

Variable type test function

is_bool()

is_int()
is_integer()
is_long()
is_string()
is_float()
is_double()
is_real()
is_array()
is_object()
is_resource()
is_null()
is_scalar()
is_numberic()
is_callable()

Notes on reading the manual

1. Regular function

bool copy (string source, string dest)
2. With mixed, mixed means that any type of data can be passed
bool chown (string filename, mixed user)
3. Functions with & parameters, indicating reference assignment. This parameter cannot be passed by value, only a variable can be passed, and then the function changes the value of the variable. When we use this variable, the value also changes
bool arsort (array &array [, int sort_flags] )

4. The default function is a function with [], indicating that this parameter is optional. If you pass a value, the value you passed will be used. If there is no value, the default value will be used.

Directly when declaring the function , give an initial value to the parameter.
Optional and required values ​​must be set from back to front
bool arsort (array &array [, int sort_flags])

5. Parameter function with... means that any number of parameters can be passed

int array_unshift ( array &array, mixed var [, mixed ...] )

6. The callback function has callback, that is, when calling this function, we need to pass in a function (function name, function name string)

array array_filter (array input [, callback callback] )