Download>Using from C>Xcode

These instructions show how to setup a basic VLFeat project with Apple Xcode. For the sake of simplicty, we create a command line tool written in C. However, these steps apply with minor modifications to other project types and to the C++ lanuage.

First, let us create a new project called ``vlfeat-client. Open Xcode and select File > New Project > Command Line Utility > Standard Tool and click Choose. Give a name to your project (in our case ``vlfeat-client), and click Save.

Now we need to add VLFeat to the C compiler include search path. To do this, select the ``vlfeat-client target and open the information panel (the blue button, or Command-i). Then select the Build panel, search for the field Header Search Paths, and add VLFeat root path (in our case this is just ``~/src/vlfeat).

Next, we add the ``libvl.dylib library file to the project resources so that Xcode links against it. To do this, drag and drop the ``libvl.dylib file (in our example ``~/src/vlfeat/bin/maci/libvl.dylib) to the left panel and click Add.

Next, edit the ``main.c source file and type the following code:

    #include <vl/generic.h>

    int main (int argc, const char * argv[]) {
      VL_PRINT ("Hello world!") ;
      return 0;
    }

If you try to build the project, it should compile without errors (if you are using C++, do not forget to wrap the ``include statements in a ``extern "C" {} block). However, if you try to run the program, it will fail, complaining that it cannot find the library image.

The reason is that ``libvl.dylib is compiled with the library ``install_name equal to ``@loader_path/libvl.dylib. This causes the run-time loader to look for the library in the same directory of the executable. There are two ways around this problem: The first is to install the library in a standard location (e.g. ``/usr/local/lib) and use the ``otool command to change the library ``install_name. The other is to simply copy the ``libvl.dylib file in the executable directory. Here we demonstrate the second technique.

To copy ``libvl.dylib in the executable directory, we add a Copy Files build phase to the project. Right-click the ``vlfeat-client target in the project panel and select Add > New Build Phase > New Copy Files Build Phase. Select Destination: Executables. Then drag-and-drop the ``libvl.dylib item from the panel to the Copy Files build phase.

Now rebuild the project, and run it. It should run correctly, and if you open the debugger console you should see this: