Changing User-Defined Global Variable Value in ExpressionEngine

Say I've got a global variable which I'm accessing inside a PHP block, which compare开发者_高级运维s to a querystring... if the comparison is true I want to set the value for a global EE variable so that all the other template pages can recognise that the value is not what it normally is - is this possible, or are the global user-defined variables constants?

Thanks, Dan

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$this->EE->config->_global_vars['foo'] = 'bar';

But keep in mind that the variable may have already been parsed before you have a chance to change it, depending on where and how it's used (see EE2's parse order discusssion).

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You can use the PHP $GLOBAL Superglobal Array, for such cases. Say you have written a variable in any block of a particular page as $a = 123;.
Now in the same page, but in another block, you can easily change it to something else as $GLOBALS['a'] = 456;.

Hope it helps.