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Old 11-21-2006, 07:32 AM   #1
rylan76
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Registered: Apr 2004
Location: Potchefstroom, South Africa
Distribution: Fedora 17 - 3.3.4-5.fc17.x86_64
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How to selectively use GCC 3.4 -OR- GCC 4.1 in FC6 when compiling?


Hi

I'm upgrading to FC6 next month, and I've been reading up on possible problems I might encounter.

One thing that seems to pop up quite promintently is that GCC 4.1 in FC6 won't neccessarily compile GCC 3.4 compliant programs (especiall for C++) which means that I anticipate some trouble getting all the packages I need (that worked and compiled fine on FC3, on my old setup) to compile under FC6, with GCC 4.1, for my new setup.

I know about the

compat-libstdc++-33
compat-libstdc++-296

packages that gives GCC 3.4 "back" to you under FC6.

My question is simple: how do I use the "old" GCC 3.4 instead of GCC 4.1??? If I install these pacakges above, do they remove / overwrite GCC 4.1? Is there some way to have both on the system and then switch between them, for example to be able to try a compile with 4.1, and if it fails try 3.4 with GNU autotools packages? And also with non-autotools packages?

I. e. I want to try and compile everything I need for FC6 with GCC 4.1 (to take advantage of new features and optimisations), and if a compile fails for a vital C++ package,"fall back" on GCC 3.4 to compile that particular C++ package that won't compile under 4.1.

Possible? Apparently so. But how is it done? How can I
"change" the two GCC versions around at will so I can always fall back on 3.4 if 4.1 fails on a C++ package?

ANY help appreciated!

Thanks
 
Old 11-21-2006, 10:01 AM   #2
tamal
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Registered: Mar 2006
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Quote:
Originally Posted by rylan76
My question is simple: how do I use the "old" GCC 3.4 instead of GCC 4.1??? If I install these pacakges above, do they remove / overwrite GCC 4.1? Is there some way to have both on the system and then switch between them, for example to be able to try a compile with 4.1, and if it fails try 3.4 with GNU autotools packages? And also with non-autotools packages?

I. e. I want to try and compile everything I need for FC6 with GCC 4.1 (to take advantage of new features and optimisations), and if a compile fails for a vital C++ package,"fall back" on GCC 3.4 to compile that particular C++ package that won't compile under 4.1.

Possible? Apparently so. But how is it done? How can I
"change" the two GCC versions around at will so I can always fall back on 3.4 if 4.1 fails on a C++ package?
1. You can edit your Makefile by replacing CC=gcc to CC=gcc34
2. You can configure gcc by using alternatives command.
3. you can manually create symbolic link to gcc34. In this case do the following:
# cd /usr/bin
# mv gcc gcc41
When you want gcc 3.4:
# ln -s /usr/bin/gcc34 /usr/bin/gcc
When you want gcc 4.1:
# ln -s /usr/bin/gcc41 /usr/bin/gcc

Now, the second part:
I had a bitter experience to implement "fall back". But it can be made. You know one thing: we can use the return value of a command to determine whether the command has ran successfully or not. So, we can write a bash or Perl script to implement this idea. I think, 'make' do not have such type of provision.
 
Old 11-22-2006, 12:36 AM   #3
rylan76
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Registered: Apr 2004
Location: Potchefstroom, South Africa
Distribution: Fedora 17 - 3.3.4-5.fc17.x86_64
Posts: 1,518

Original Poster
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Thanks Tamal!

That'll definitely help.
 
  


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