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Old 02-29-2012, 05:54 PM   #1
bjdodo
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dependency introduced breaking change, how to workaround with automake


Hi

I am maintaining an application that I wrote a long time ago, in c++. I am facing an issue now in that a library I use has changed the signature of one of its functions. So the code I have builds on ubuntu (ubuntu has an old version of this library in its repos), but it does not build on archlinux (archlinux is bleeding edge). If I fix the code on archlinux, it breaks on ubuntu.

I have read that you can achieve that some defines can be created by the automake tool, depending on the version of the library that I could use in my c++ code. The way I imagine it is that I run ./configure, then it will detect the version of the library, will decide whether it is old or new and then it will define constants. So in my c++ code I can do this:

#ifdef NEWLIBRARY
libfunction(1,2,3); // new signature
#else
libfunction(1,2); // old signature
#endif

Could someone please describe how it works, and could you please give me a few pointers like an example that does this or some keywords that can be used in configure.ac to achieve this?

Thank you and best regards,
Jozsef
 
Old 03-01-2012, 12:26 AM   #2
ntubski
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In general you can use AC_DEFINE to pass information from configure into your code.

But usually, a library should have some way of getting the version from the code.

Also, note that
Quote:
The Autoconf approach to portability is to test for features, not for versions.

http://en.wikipedia.org/wiki/Autoconf#Approach
 
Old 03-01-2012, 04:58 PM   #3
bjdodo
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Hi

Thank you for your answer.

Quote:
The Autoconf approach to portability is to test for features
That is a great approach! But where do I start? How does this work?

Thank you again,
Jozsef
 
Old 03-01-2012, 10:50 PM   #4
firstfire
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Hi.

You can write a simple check to test if it compiles with your library successfully. Look here.
 
Old 03-02-2012, 12:55 PM   #5
bjdodo
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Hi firstfire,

Using the page you have given I have solved it with versioning. Possibly the compiling thing would be a bit more robust, but for this, for now it does not matter.

Here are the details, if someone is interested, search for PKG_CHECK_MODULES on this page:
https://sites.google.com/site/jozsef...tents/automake

Also here is a real life example, search for MEDIASTREAMER28:
http://gtalx.svn.sourceforge.net/vie...42&view=markup
and here is the .h file (note that ../../config.h is included):
http://gtalx.svn.sourceforge.net/vie...42&view=markup

BTW I find it amazing that ./configure can try to build small snippets to see if a function is supported on the user's PC. This is the best technology I have seen; automake has grown a lot in my eyes :-)

Thank you very much for your help!
Jozsef
 
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Old 03-02-2012, 10:03 PM   #6
ntubski
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Quote:
AC_MSG_NOTICE([Error - gloox is required to build the app])
You might want to use AC_MSG_WARN or AC_MSG_ERROR for this.
 
  


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