.dylibs and .a files: Some guidance

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Level 1

1 points

.dylibs and .a files: Some guidance

As far as I understand, .dylib files are dynamic libraries and .a files are static libraries.

Both have their headers in a separate place. Most 3rd party libraries come in the form of .dylib files, but there are some occasions where I have encountered both of them for one library, such as libpng when installed using Fink.

My question is this:

-What is the proper way to link your Xcode project against a .dylib or a .a file?
-In case the .a file has a .dylib file with the same name in the same installation directory, could it be that the .a file depends on the .dylib file?
-How can I make link my program against a .a or a .dylib file and then make it run on other machines apart from my own?

What I am trying to do is to build a project using OpenGL, and libpng, for loading png images and displaying them. I am searching Apple's documentation, and I cannot find any relevant text. Please help!

Message was edited by: Soulstorm

Intel iMac 17", Mac OS X (10.5.6), 2 connected external firewire HDDs, working with Dual Screen

Posted on Feb 5, 2009 4:18 PM

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Answer 1

ericmeyers

Level 4

1,410 points

Feb 6, 2009 5:29 AM in response to Soulstorm

Soulstorm wrote:
OK, thanks a lot. let me ask 2 more questions:

1)So, what about header files? Must I also include them in my project? The end user might not have installed this library in his system, so, apparently, the header library might not be there. So, I must include both the .a (or .dylib file) AND the header in my Xcode project?

Yes your project needs access to the headers. Once it's compiled you don't need them so you don't have to distribute the headers.

2)Why do some libraries come in both .a and .dylib files? What's the purpose of having both versions instead of just distributing one of them?

Just to give you the option of linking against either. Choosing the dynamic option makes your executable smaller and if for some reason the dylib changes you don't have to recompile.
There are lots of other advantanges and disadvantages to both, such as loading a .dylib at runtime which you haven't encountered yet.

Message was edited by: Soulstorm

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Answer 2

ericmeyers

Level 4

1,410 points

Feb 5, 2009 4:44 PM in response to Soulstorm

Soulstorm wrote:
As far as I understand, .dylib files are dynamic libraries and .a files are static libraries.

Yup.

Both have their headers in a separate place. Most 3rd party libraries come in the form of .dylib files, but there are some occasions where I have encountered both of them for one library, such as libpng when installed using Fink.

My question is this:

-What is the proper way to link your Xcode project against a .dylib or a .a file?

Drag the file into Xcode.

-In case the .a file has a .dylib file with the same name in the same installation directory, could it be that the .a file depends on the .dylib file?

Ah, tricky. Xcode will always link the dylib no matter what you try to do if the .a file has the same name. What I do is create a symbolic link to the .a file with a different name and drag that in if I want to link statically.

-How can I make link my program against a .a or a .dylib file and then make it run on other machines apart from my own?

If you link against .a nothing to do. It becomes part of your executable. If you link against the .dylib then you have to distribute that file with your app.

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Answer 3

Soulstorm Author

Level 1

1 points

Feb 6, 2009 1:23 AM in response to ericmeyers

OK, thanks a lot. let me ask 2 more questions:

1)So, what about header files? Must I also include them in my project? The end user might not have installed this library in his system, so, apparently, the header library might not be there. So, I must include both the .a (or .dylib file) AND the header in my Xcode project?

2)Why do some libraries come in both .a and .dylib files? What's the purpose of having both versions instead of just distributing one of them?

Message was edited by: Soulstorm

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Answer 4

Soulstorm Author

Level 1

1 points

Feb 6, 2009 1:01 PM in response to ericmeyers

Thanks a lot. That solved all of my questions.

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