return day of week when timestamp passed into date function php

I am trying to re开发者_如何转开发turn the day of the week based on the date that i pass into the date() function but it's not working. I have this:

echo date('N');
echo date('N', '2011-05-11');

Today is thursday, so these both return 4 no matter what I pass into it for a date. What am I doing wrong?

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echo date('N', strtotime('2011-05-11'));

date expects a timestamp as a second parameter, thats why you need to convert your string to a valid timestamp.

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I think you need to use "D" instead of "N". N returns the index of the day and D returns the name.