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Re: string manipulation : removing a part of a string

From: Eric Blake
Subject: Re: string manipulation : removing a part of a string
Date: Mon, 18 Jun 2012 07:03:45 -0600
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On 06/15/2012 11:49 PM, Vincent Torri wrote:

>> This can be shortened:
>> m4_pushdef([flagm4], m4_bpatsubst([[$2]], [no-]))
>> since m4_bpatsubst is a no-op if the pattern 'no-' doesn't appear.

> heh, as option=m4_bpatsubst([[$2]], [no-]) is working, there's no need.
> It's so simple when you know how it works...
> I finally found the doc of that m4 macro, and it's not mentioned that
> it's a no op in some cases:
> is it possible to add that ?

Patches welcome, if you think it would help.  The current documentation
for m4_bpatsubst() just points to the GNU M4 manual for patsubst():

> Also, if I'm not mistaken, there's a typo in the macro name :
> m4_bpatsubsts (final s)
>             ^

Wrong macro.  m4_bpatsubsts() with the final s is a different macro,
with even more power than m4_bpatsubst().

>> m4_foreach_w([flag], [$2],
>> [EFL_CHECK_COMPILER_FLAG([$1], m4_defn([flag]))])
> for $1, i was sure, but why is it not needed for m4_defn([flag]) ?

Because you _want_ the m4_defn() to be expanded up front, and because
the output of m4_defn is already quoted for reuse.  In other words, you
want to call:

EFL_CHECK_COMPILER_FLAG([efl], [-Wno-bar])

and not:

EFL_CHECK_COMPILER_FLAG([efl], [m4_defn([flag])])
EFL_CHECK_COMPILER_FLAG([efl], [m4_defn([flag])])

because the latter wouldn't be checking the right flag names.

Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library

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