问题
Could anyone explain differences between error_reporting(E_ALL); and error_reporting(E_ALL & ~E_NOTICE); ?
I noticed that when I change from E_ALL to E_ALL & ~E_NOTICE, an error which I was hacking, disappears.
回答1:
E_ALL is "everything"
E_ALL & ~E_NOTICE is "everything except notices"
Notices are the least-urgent kinds of messages. But they can be very useful for catching stupid programmer mistakes, like trying to read from a hash with a non-existent key, etc.
(To understand the syntax, read up on bitwise operators)
回答2:
E_ALL would should all the error and warning and notice - everything
E_NOTICE is a special error level, showing things that won't produce error but are not good or gonna be obsolete in future release of PHP. The notice error level is meant to encourage best practices.
Also it should be error_reporting(E_ALL ^ E_NOTICE); to report everything except notice.
You are advice during development to set the error reporting to E_ALL and fix all the notice errors.
a look in the manual would give much more details.
回答3:
E_ALL is a flag E_NOTICE is a flag as well
so when you do bitwise operation of ~ which is NOT you'll exclude E_NOTICE from E_ALL
Under the hood following happens
in decimal
E_ALL = 32767
E_NOTICE = 8
they are power of 2
bitwise
E_ALL = 111111111111111
E_NOTICE = 000000000001000
result of NOT will be
111111111110111
then php can internally check if notices are ON with &(AND) operator
111111111110111
000000000001000
1 & 0 = 0 it means it is turned off. If however you didn't use ~ NOT then it would be 1 & 1 = 1 it means that flag is SET
There are other options for example OR to turn on the flag, or XOR to change the flag to opposite state. Basically, this is how flags work.
来源：https://stackoverflow.com/questions/1678859/what-are-differences-between-error-reportinge-all-and-error-reportinge-all