In the static case, it doesn't really matter, because you don't actually link static libraries - all you do is pack some object files together in one archive. All you have to is compile your object files, and you can create static libraries right away.

The situation with dynamic libraries is more convoluted, there are two aspects:

1. A shared library works exactly the same way as static library (except for shared segments, if they are present), which means, you can just do the same - just link your shared library as soon as you have the object files. This means for example symbols from libDA will appear as undefined in libDB

2. You can specify the libraries to link to on the command line when linking shared objects. This has the same effect as 1., but, marks libDB as needing libDA.

The difference is that if you use the former way, you have to specify all three libraries (-lDA, -lDB, -lDC) on the command line when linking the executable. If you use the latter, you just specify -lDC and it will pull the others automatically at link time. Note that link time is just before your program runs (which means you can get different versions of symbols, even from different libraries).

This all applies to UNIX; Windows DLL work quite differently.

Edit after clarification of the question:

Quote from the ld info manual.

The linker will search an archive only once, at the location where it is specified on the command line. If the archive defines a symbol which was undefined in some object which appeared before the archive on the command line, the linker will include the appropriate file(s) from the archive. However, an undefined symbol in an object appearing later on the command line will not cause the linker to search the archive again.

See the `-(' option for a way to force the linker to search archives multiple times.

You may list the same archive multiple times on the command line.

This type of archive searching is standard for Unix linkers. However, if you are using `ld' on AIX, note that it is different from the behaviour of the AIX linker.

That means:

Any static library or object that depends on other library should be placed before it in the command line. If static libraries depend on each other circularly, you can eg. use the -( command line option, or place the libraries on the command line twice (-lDA -lDB -lDA). The order of dynamic libraries doesn't matter.

Important: This check should always be performed asynchronously. The majority of answers below are synchronous so be careful otherwise you'll freeze up your app.

Swift

1. Install via CocoaPods or Carthage: https://github.com/ashleymills/Reachability.swift

2. Test reachability via closures

   let reachability = Reachability()!
   
   reachability.whenReachable = { reachability in
       if reachability.connection == .wifi {
           print("Reachable via WiFi")
       } else {
           print("Reachable via Cellular")
       }
   }
   
   reachability.whenUnreachable = { _ in
       print("Not reachable")
   }
   
   do {
       try reachability.startNotifier()
   } catch {
       print("Unable to start notifier")
   }
   

Objective-C

1. Add SystemConfiguration framework to the project but don't worry about including it anywhere

2. Add Tony Million's version of Reachability.h and Reachability.m to the project (found here: https://github.com/tonymillion/Reachability)

3. Update the interface section

   #import "Reachability.h"
   
   // Add this to the interface in the .m file of your view controller
   @interface MyViewController ()
   {
       Reachability *internetReachableFoo;
   }
   @end
   

4. Then implement this method in the .m file of your view controller which you can call

   // Checks if we have an internet connection or not
   - (void)testInternetConnection
   {
       internetReachableFoo = [Reachability reachabilityWithHostname:@"www.google.com"];
   
       // Internet is reachable
       internetReachableFoo.reachableBlock = ^(Reachability*reach)
       {
           // Update the UI on the main thread
           dispatch_async(dispatch_get_main_queue(), ^{
               NSLog(@"Yayyy, we have the interwebs!");
           });
       };
   
       // Internet is not reachable
       internetReachableFoo.unreachableBlock = ^(Reachability*reach)
       {
           // Update the UI on the main thread
           dispatch_async(dispatch_get_main_queue(), ^{
               NSLog(@"Someone broke the internet :(");
           });
       };
   
       [internetReachableFoo startNotifier];
   }
   

Important Note: The Reachability class is one of the most used classes in projects so you might run into naming conflicts with other projects. If this happens, you'll have to rename one of the pairs of Reachability.h and Reachability.m files to something else to resolve the issue.

Note: The domain you use doesn't matter. It's just testing for a gateway to any domain.