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(PECL apc >= 3.0.0)

apc_define_constants Defines a set of constants for retrieval and mass-definition


apc_define_constants ( string $key , array $constants [, bool $case_sensitive = TRUE ] ) : bool

define() is notoriously slow. Since the main benefit of APC is to increase the performance of scripts/applications, this mechanism is provided to streamline the process of mass constant definition. However, this function does not perform as well as anticipated.

For a better-performing solution, try the » hidef extension from PECL.

Note: To remove a set of stored constants (without clearing the entire cache), an empty array may be passed as the constants parameter, effectively clearing the stored value(s).



The key serves as the name of the constant set being stored. This key is used to retrieve the stored constants in apc_load_constants().


An associative array of constant_name => value pairs. The constant_name must follow the normal constant naming rules. value must evaluate to a scalar value.


The default behaviour for constants is to be declared case-sensitive; i.e. CONSTANT and Constant represent different values. If this parameter evaluates to FALSE the constants will be declared as case-insensitive symbols.

Return Values

Returns TRUE on success or FALSE on failure.


Example #1 apc_define_constants() example

= array(
'ONE'   => 1,
'TWO'   => 2,
'THREE' => 3,

The above example will output:


See Also

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User Contributed Notes 2 notes

jmucchiello AT yahoooooooo DOT com
10 years ago
It doesn't introduce much overhead if you make use of conditional function definitions:

if (function_exists('apc_load_constants')) {
define_array($key, $arr, $case_sensitive = true)
        if (!
apc_load_constants($key, $case_sensitive)) {
apc_define_constants($key, $arr, $case_sensitive);
} else {
define_array($key, $arr, $case_sensitive = true)
        foreach (
$arr as $name => $value)
define($name, $value, $case_sensitive);

//in your code you just write something like this:

define_array('NUMBERS', Array('ONE' => 1, 'TWO' => 2, 'THREE' => 3));
webmaster at thedigitalorchard dot ca
10 years ago
An observation that I've made is that the nature of apc_define_constants() binding the list of constants to a key and then requiring that key to load the constants is limiting. Furthermore, there's no way to append additional constants to a given key.

A solution that I've been adopting is to build a list of constants to be defined, and then do one of two things:

1) if APC is enabled, then use apc_define_constants();
2) ...else loop through the list and define each constant normally.

The problem I've run into is when this process happens at different places in a large application, it can introduce overhead that otherwise wouldn't be there if it was possible to append to an existing list of defined constants in APC.
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