I want to check the output of the preprocessor for some files. How can I view the preprocessor's output in Xcode?

You can choose the "Show the Assistant editor" view in the top right set of buttons in the toolbar. <img src="https://i.stack.imgur.com/H5ssx.png" alt="enter image description here"> Then, at the top of the right-hand editor you can click the little <code>Related Files</code> button and then either choose <code>Preprocess</code> or <code>Assembly</code>. <img src="https://i.stack.imgur.com/wxCW7.png" alt="enter image description here"> You can see an example of both the preprocessor output and generated assembly code all side-by-side here: <img src="https://i.stack.imgur.com/8VLUI.jpg" alt="enter image description here">