ini_set()

(PHP 4, PHP 5, PHP 7)

为一个配置选项设置值

说明

设置指定配置选项的值。这个选项会在脚本运行时保持新的值，并在脚本结束时恢复。

参数

不是所有有效的选项都能够用ini_set()来改变的。这里有个有效选项的清单附录。

选项新的值。

返回值

成功时返回旧的值，失败时返回FALSE。

范例

设置一个 ini 选项

参见

• get_cfg_var() 获取 PHP 配置选项的值
• ini_get() 获取一个配置选项的值
• ini_get_all() 获取所有配置选项
• ini_restore() 恢复配置选项的值
• 如何改变配置选项

I have experienced on some systems that ini_set() will fail and return a false, when trying to set a setting that was set inside php.ini inside a per-host setting. Beware of this.

[[[Editors note: Yes, this is very true. Same with 
register_globals, magic_quotes_gpc and others.
]]]
Many settings, although they do get set, have no influence in your script.... like upload_max_filesize will get set but uploaded files are already passed to your PHP script before the settings are changed.
Also other settings, set by ini_set(), may be to late because of this (post_max_size etc.).
beware, try settings thru php.ini or .htaccess.

When checking for the success of ini_set(), keep in mind that it will return the OLD value upon success - which may have been "0". Therefore you cannot just compare the return value - you have to check for "identity":

This explains reported situations where ini_set() "always" seems to fail!

set PHP_INI_PERDIR settings in a .htaccess file with 'php_flag' like this:
php_flag register_globals off
php_flag magic_quotes_gpc on

Be careful with setting an output_handler, as you can't use ini_set() to change it. *sigh*
In my php.ini I have this for my web pages (and I want it): 
 output_handler = ob_gzhandler
But this causes my command line scripts to not show output until the very end.
#!/usr/bin/php -q

root@# ./myscript.php
output_handler => ob_gzhandler
Apparently (acording to Richard Lynch):
> TOO LATE!
> The ob_start() has already kicked in by this point.
> ob_flush() until there are no more buffers.

If it's not your server and therefore you want to hide the data in your session variables from other users, its very useful to set the session.save_handler in your scripts to shared memory with:

Remember: You have to set it in every script that uses the session variables BEFORE "session_start()" or php won't find them.

When your ISP does not allow you to add the default include directories - it might be useful to extend the 'include_path' variable: 

[[[Editors note: Just because you're able to set something 
doesn't mean it will work as expected. Depends on the 
setting. For example. setting register_globals at 
runtime will be of little use as its job has already 
been completed by the time it reaches your script.
]]]
When a setting can not be changed in a user script, the return value of ini_set is "empty", not "false" as you may expect.
If you check in your script for return value is "false" the script will continue processing, although the setting has not been set.
The boolean return value is used for settings that can be changed in a script. Otherwise the empty value is returned.
To test for both error conditions use: 

if u receive an Error with generic like :
Maximum execution time of 30 seconds exceeded 
if u set ini_set(max_execution_time, 300);
your problem will be solved 
pls note that the 300 , is 300 seconds , which means 5 minute you can set another value !

Note that this function only works with PHP_INI_ALL options!

ini_set('display_errors', 1);
error_reporting(E_ALL);

To change settings from .htaccess files, it is also required that the directory permissions configured in Apache allow this.
The  entry in httpd.conf MUST contain "AllowOverride All" or at least "AllowOverride Options" to read PHP settings from the .htaccess file.
E.g. in Fedora Core 2, the default settings for /var/www/html/ are "AllowOverride None", so changing PHP settings via .htaccess for applications installed below /var/www/html/ will not work.

I figured out why php dont output errors such as an expected ';' on code and output a 500 error. Some server are configured to omit php errors on pages using the directive display_errors=Off;
In most cases, the server will output a 500 Internal Server Error instead of php error because of it. 
To prevent this default you must set this directive directly in the php.ini file and the server will show you the php error properly. Setting ini_set('display_errors', true) on-the-fly wont work.

While this doesn't belong in the manual, it should be useful for people looking on this page for zend_optimizer.* ini options, which are commonly installed:
Information on the "zend_optimizer.optimization_level" and "zend_optimizer.enable_loader" options is available at:
http://www.zend.com/support/user_docs/ZendOptimizer/PDF/ZendOptimizer_UserGuide.pdf

Careful - in some cases, when setting zlib.output_compression to "On" via ini_set, PHP won't send the Content-type header and browsers will garble the output. Set it to the desired buffer size instead, which sends the correct header: 

If you use gz_handler you might want to switch over to 
zlib.output_compression
This can be controlled via the ini_set control.

or 

If you set something using php_admin_value in httpd.conf it is then not possible to be set the value at runtime, even if it's NOT PHP_INI_SYSTEM. 
Just an interesting note for Server admins this might come in handy to disable setting of certain things... like allow_url_fopen.
- Davey

To find the apache php settings try something like this.
> cd /etc/apache2
> grep -r -n -i safe_mode_exec_dir *.conf
or
> grep -r -n -i safe_mode.*On *.conf
If you find a gererated file, obviously you need to find the source template for it, to change what's needed there.
I just wasted a sunny Sunday on searching for where the heck safe_mode_exec_dir was changed.
And yes, Local Value in phpinfo does mean 'changed between the php.ini file and here', as you would think.
If you have an automated virtual host configuration, such as confixx, php ini values can be spread across very many files.
They can be changed in apache config files, that can have any name, but usually will end on .conf, besides in .htaccess files.

Whilst most boolean settings can be disabled by passing '0', 'Off' or `No' (in fact anything that is not '1', 'On' or 'Yes' - not case-sentive) to ini_set(), it should be noted that ini_get() returns the literal string as set. So if you later want to check this setting by calling ini_get() and it's been set to 'Off' (a non-empty string that evaluates to True), then you'll have to specifically check for this in a (case-insensitive) string comparison, rather than the simpler:
if (ini_get('config_setting')) { /* ... */ }
So, if you need to disable boolean settings I think it's preferable to set them to '0' (which simply evaluates to False).

How to get xdebug var_dump to show full object/array regardless to php,ini settings:
ini_set("xdebug.var_display_max_depth", -1);
ini_set("xdebug.var_display_max_children", -1);
ini_set("xdebug.var_display_max_data", -1);
var_dump($test);

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