Earlier chapters in the book mention various PHP configuration directives. These are settings that affect the behavior of the PHP interpreter, such as how errors are reported, where the PHP interpreter looks for included files and extensions, and much more.
Read this section when you encounter a configuration directive you want to alter or
are curious as to how you can tweak the PHP interpreter's settings (whether you are
using PHP on your own computer or with a hosting provider). For example, changing the
output_buffering directive (as discussed in Section 8.6) makes your life much easier if
you are working with cookies and sessions.
The values of configuration directives can be changed in a few places: in the PHP interpreter's php.ini configuration file, in Apache's httpd.conf or .htaccess configuration files, and in your PHP programs. Not all configuration directives can be changed in all places. If you can edit your php.ini or httpd.conf file, it's easiest to set PHP configuration directives there. But if you can't change those files because of server permissions, then you can still change some settings in your PHP programs.
The php.ini file holds system-wide configuration for the PHP
interpreter. When the web server process starts up, the PHP interpreter reads the
php.ini file and adjusts its configuration accordingly. To find
the location of your system's php.ini file, examine the output from
phpinfo( ) function. This function prints ...