by Joseph Long

After my recent Xcode learning experience, I thought I would see if I could accomplish the same things without it. It turns out that it’s pretty straightforward to use a plain old Makefile to create a nice double-clickable .app bundle.

Makefiles are almost as old as Mac OS X’s UNIX underpinnings themselves, and pretty simple to use. The command line make tool checks the nearest Makefile for instructions, and then, well, makes the build happen.

In it’s simplest form, you don’t need any Makefile at all. If you have a file called foo.c, typing make foo in the same directory will produce a binary called foo by compiling foo.c using your system’s C compiler (e.g. the one installed with Xcode). More sophisticated things, like creating a .app bundle, can be done by adding some variables and targets to the Makefile.

Similar to last time, I have made a folder for this project. SDL2.framework is installed in my home directory under ~/Library/Frameworks/, and Xcode and OS X are up to date.

Step 1: Create our main.c

We’ll use the same code as last time, at least to start. Save this as main.c (or whatever you like, but remember to change later directions accordingly).

#include <SDL2/SDL.h>

int main(int argc, const char * argv[]){
    if(SDL_Init(SDL_INIT_EVERYTHING) != 0)
    {
        puts("SDL_Init error");
        return -1;
    } else {
        puts("SDL_Init success!");
        return 0;
    }
}

What’s in an .app?

That which we call a program, by any other name would smell as sweet…

App bundles are a clever way of moving executables and their associated resources around while convincing the user that they’re one big file. Really, they’re just folders with names ending in .app, and a few special folders and files that OS X looks for. They are:

We know where to find the SDL2 framework, and we will build our binary shortly, but what about Info.plist? We’ll have to steal one from an existing app and modify it. Right- or Control-click on an existing app (say, TextEdit) and choose “Show Package Contents”. Inside the app, you should see an Info.plist. Open it in your favorite text editor and have a look. (What the hell is all that?, you’re probably thinking.)

Fortunately, it turns out that we can remove most of those properties and still have an app bundle that works. Here’s the template I came up with based on the minimal app from last time with Xcode:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>CFBundleExecutable</key>
    <string>APP_NAME</string>
    <key>CFBundleIdentifier</key>
    <string>com.your-name.APP_NAME</string>
    <key>CFBundleInfoDictionaryVersion</key>
    <string>6.0</string>
    <key>CFBundleName</key>
    <string>APP_NAME</string>
    <key>CFBundlePackageType</key>
    <string>APPL</string>
</dict>
</plist>

Fill in your-name appropriately, then save this as Info.plist in the same directory as your Makefile.

Step 2: Building a Bundle

Before we automate this with a Makefile, it’s good practice to make sure you can put it all together in the terminal. After all, make just runs your commands!

I’m calling my application SDLExample2 (original, I know). I’m putting it in a build directory just to keep things organized. (This way I can ignore the whole folder with .gitignore, no matter what build products I eventually have.)

  1. Make the .app folder and essential subfolders

    mkdir -p ./build/SDLExample2.app/Contents/{MacOS,Resources}
    
  2. Compile main.c to make an executable for the bundle

    cc -F "$HOME/Library/Frameworks" -framework SDL2 main.c -o main
    

    As you can probably guess, -F specifies a folder with frameworks in it. -framework indicates the name of a framework to link with. If you run it in the terminal you should see something like:

    $ ./main
    SDL_Init success!
    
  3. Copy the resulting binary into place

    cp ./main ./build/SDLExample2.app/Contents/MacOS/SDLExample2
    
  4. Copy the SDL2 framework into Resources

    cp -R "$HOME/Library/Frameworks/SDL2.framework" ./build/SDLExample2.app/Contents/Resources/
    
  5. Copy in the Info.plist file…

    cp Info.plist ./build/SDLExample2.app/Contents/
    

    …and edit it with your favorite text editor. It should look like this, unless you’ve named the app something other than SDLExample2:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>CFBundleExecutable</key>
    <string>SDLExample2</string>
    <key>CFBundleIdentifier</key>
    <string>com.joseph-long.SDLExample2</string>
    <key>CFBundleInfoDictionaryVersion</key>
    <string>6.0</string>
    <key>CFBundleName</key>
    <string>SDLExample2</string>
    <key>CFBundlePackageType</key>
    <string>APPL</string>
</dict>
</plist>

Now you should have an app! An app that doesn’t do much! Double click the SDLExample2 icon in the build folder and see. If you don’t get any error messages about corrupted or incomplete applications, you’re good to go.

Step 3: Make the computer build you a bundle

I was afraid of make and Makefiles for a long time, but I eventually figured out that my fear was from seeing Makefiles made to do things they really ought not to do. It’s not a very good language in which to write scripts!

For simple tasks, however, they are more than adequate. Here is my Makefile to automate everything we did in Step 2.

FRAMEWORK_PATH=$(HOME)/Library/Frameworks
APP_NAME=SDLExample2
CFLAGS=-F $(FRAMEWORK_PATH) -framework SDL2

all: main clean_app package_app

clean_app:
    rm -rf "./build/$(APP_NAME).app/"

package_app:
    mkdir -p "./build/$(APP_NAME).app"/Contents/{MacOS,Resources}
    cp -R "$(FRAMEWORK_PATH)/SDL2.framework" "./build/$(APP_NAME).app/Contents/Resources/"
    cp Info.plist "./build/$(APP_NAME).app/Contents/"
    sed -e "s/APP_NAME/$(APP_NAME)/g" -i "" "./build/$(APP_NAME).app/Contents/Info.plist"
    cp ./main "./build/$(APP_NAME).app/Contents/MacOS/$(APP_NAME)"

(n.b. These should be actual tab characters indenting lines in the Makefile, not spaces.)

The Makefile begins with some variable definitions of the form FOO=bar. Including the value of one variable in another is done with the $(FOO) construct. (We don’t quote variables defined in Makefiles, as the quotes are interpreted literally.) CFLAGS is important, since it sets up extra arguments to be passed to the C compiler (like the ones in step 2.2).

The all target is special, as it is built (or run) when make is invoked without target names. Here we tell it to “build main, remove any existing app bundle, and build the app bundle again from scratch”.

The clean_app target just removes the entire bundle folder.

The package_app target is basically the commands we did, one by one, in Step 2. The only thing different here is the use of seds in-place-editing mode (-i "") to replace APP_NAME with our app name defined in the beginning of the Makefile.

Also, note that we have quotes around arguments that include $(APP_NAME). This is so you won’t confuse the shell if you set APP_NAME to something with spaces in it (e.g. APP_NAME=SDL Example 2).

Making make make

Remove the main binary and app bundle, if they exist, then run make with no arguments. You should see something like this:

# make
cc -F /Users/josephoenix/Library/Frameworks -framework SDL2    main.c   -o main
rm -rf "./build/SDLExample2.app/"
mkdir -p "./build/SDLExample2.app"/Contents/{MacOS,Resources}
cp -R "/Users/josephoenix/Library/Frameworks/SDL2.framework" "./build/SDLExample2.app/Contents/Resources/"
cp Info.plist "./build/SDLExample2.app/Contents/"
sed -e "s/APP_NAME/SDLExample2/g" -i "" "./build/SDLExample2.app/Contents/Info.plist"
cp ./main "./build/SDLExample2.app/Contents/MacOS/SDLExample2"

Look in the ./build/ directory. Do you see an app bundle?

You don’t need Xcode to build an app bundle after all!

I know I should check my shell-based privilege here, but this took me all of one flight to figure out. (It was a short flight too! ATL to BWI.) On the other hand, I futzed around with Xcode for an entire evening to write that other post.

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