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Continuous PHP testing undefined

In PHP, if I define a constant like this:

define('FOO', true);
if(FOO) do_something();

The method do_somethingexecutes as expected.

But if I do not define a constant BOObelow:

if(BOO) do_something();

Then executed as well do_something. What's going on here?

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7 answers

BOOwill be forced into a string BOOthat is not empty, so it is true.

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