What is a file with extension .a?

Question

I downloaded this: https://github.com/mongodb/mongo-c-driver

And now I'm trying to use it inside my C program, but I don't know what to do with the generated .a files. What are they? I couldn't find any information, not even in the GCC manual.

And I built it like so:

  scons --c99

Also, can I use C99 libraries with my C89 program?

Possible duplicate of *[What's the difference between .so, .la and .a library files?](https://stackoverflow.com/questions/12237282/whats-the-difference-between-so-la-and-a-library-files)*. — Peter Mortensen, Nov 26 '17 at 17:19

score 117 · Accepted Answer · edited Feb 05 '23 at 21:01

117

.a files are static libraries typically generated by the archive tool. You usually include the header files associated with that static library and then link to the library when you are compiling.

edited Feb 05 '23 at 21:01

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answered May 11 '11 at 13:40

GWW

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I thought the .so files are the library files. Do I need to use both then? – Blub May 11 '11 at 13:50
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@Blub: there are both static and shared libraries. In Linux, .a is a static library (archive), while .so is a shared library (shared object). – unwind May 11 '11 at 14:03
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You can see the contents of a `.a` static library by using `ar tv foo.a`. It's usually a collection of `.o` object files. – Keith Thompson Sep 20 '13 at 16:03
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how are they called for easy googling? – Ilia Sidorenko Feb 18 '17 at 07:03
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They are called Archive Files – GWW Feb 18 '17 at 16:27
You can use the `ar` command in macOS to extract, remove, modify files and create .a archives. – randomuser5215 Mar 08 '19 at 23:48

score 38 · Answer 2 · edited Aug 30 '18 at 13:24

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.a files are created with the ar utility, and they are libraries. To use it with gcc, collect all .a files in a lib/ folder and then link with -L lib/ and -l<name of specific library>.

Collection of all .a files into lib/ is optional. Doing so makes for better looking directories with nice separation of code and libraries, IMHO.

edited Aug 30 '18 at 13:24

Peter Mortensen

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answered May 11 '11 at 13:41

Sriram

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What exactly is the "name of library", the name of .a file or the name of the folder that included .a file, or others? – ShuangSong Feb 28 '21 at 09:38
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I tried both, they were all returned errors. – ShuangSong Feb 28 '21 at 09:50

What is a file with extension .a?

2 Answers2

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