How can I combine several C/C++ libraries into one?

You could extract the object files from each library with

ar x <library name>

and then merge them all into a new library with

ar cs <new library name> <list each extracted object file>

On Unix like systems, the ld and ar utilities can do this. Check out http://en.wikipedia.org/wiki/Ar_(Unix) or lookup the man pages on any Linux box or through Google, e.g., 'Unix man ar'.

Please note that you might be better off linking to a shared (dynamic) library. This would add a dependency to your executable, but it will dramatically reduce its size, especially if you're writing a graphic application.

I'm not sure how to physically combine them into a single file, however you could employ an abstraction of a sort and just include a single "AllMyLibs.a/h" which in turn includes everything you want. You could also put this into the location where your compiler searches for libraries, so it would work for any project.

Maybe I'm misunderstanding, but don't you only have to ship the libraries if the end-user code calls them directly? If all the access to JPEG methods, etc. is from your code in your static library, then just link the libraries into your library.

I.e.,

---------------------
| End-user EXE file |
---------------------
      |
      | makes calls to
      |
      v
 --------------------
 | Your static lib.a |
 --------------------
         | makes calls to and links
         v
     ------------------------------------ .....
     |                    |         |
  -------------    -------- ----------
  | libjpeg.a |    |libz.a| |libpng.a|
  -------------    -------- ----------

I.e., it's only an issue if the end code needs to make direct calls into libz.a, libpng.a, etc.

If the application code has a legitimate need to call libz.a, for example, then that would as mentioned above be a case for using a dynamic module.

Combining several third-party libraries into one could create more problems for you—for instance, if two of those libraries define a common symbol which your program doesn't use. Now you've got to extract all (or all-but-one) of the instances of the common symbol before you combine the libraries.