Integrating .a library file types with XCode

Question

I am testing an image capture library that sent over their code library as a regular header file and a file ending in a "*.a" extension. I am not familiar with using a file in this format and can't seem to find the right "magic" to search for.

What does this file extension stand for?

What if any extra steps are needed to get it integrated with my XCode project?

Answer 1

Maybe a bit more of theory can get you in the right track so you'll know how to search next time:

.a files are archives of object (.o) files. These object files are generally produced by an assembler, compiler, or other language translator; They contain machine code that is usually not directly executable, but are used by linker tools to generate an executable or yet another library by combining parts of these object files.

Another important thing you should know is that since these files contain machine code, they must have been compiled for the correct architecture you're targeting for (ex.: armv7, i386, etc). That can be the reason why sometimes you will be able build your project for one device but not to another if you don't have the right set of files for the targeted platform (eg iPhone simulator vs. actual iPhone).

It is also possible to have "universal binaries", which are files that in turn package together archives of object files (.a) for different architectures (eg using tools such as lipo), so that the same library file can be given to the linker for multiple architectures. Or, you may have a different linker configuration for each target (eg using conditional build settings in XCode). All of these files can be analyzed with certain tools (eg "file", "otool", "lipo -info", etc), and each has several parameters to play with. Debuggers will also check the symbols within these files for their own purposes.

When you drag the '.a' file to your project's directory within Xcode, you can notice that it will automatically add this file to the list of "Link Binary With Libraries" items under your target's "Build Phases".

Since the header files allows us to separate certain elements of a program's source code into reusable files, that commonly contain forward declarations of classes, subroutines, variables, and other identifiers that are needed for reference during the compilation step, it is common to have libraries provided as archives of compiled objects (.o) in ".a" files along with their respective headers. For instance, as soon as you include the headers files in your XCode project, the editor will provide auto-complete for these new functions.

Sometimes, you might also consider having the actual source code of the library instead of binaries inside your project as this * might * make debugging easier in case an unexpected behavior is happening inside that "library" package. Many times this is not an option though (when you have no access to the sources) when the binary distribution is made in purpose to hide implementation details (commercial libraries).

Answer 2

.a stands for archive. It is also known as a static library. I believe you should be able just to drag it and the header files into Xcode. Xcode should pick up the right thing to do from its extension.

Example, see appr. from 30 sec here http://memention.com/ac3dreader/usage/quickstart.html

Another example from Google Analytics, under Setup

Drag GANTracker.h and libGoogleAnalytics.a from the SDK's Library directory into your new project.

https://developers.google.com/analytics/devguides/collection/ios/devguide