Chapter 4.  Compilation: The Basics

Chapter 4. Compilation: The Basics Before continuing, let's review how computer programs get made. If you're coming to Xcode from long experience with GNU Make or another development environment, this discussion will be extremely familiar to you. Programmers use source code to specify what a program does; source code files contain a notation that, although technical and sometimes cryptic, is recognizably the product of a human, intended in part for humans to read and understand. Even the most precise human communication leaves to allusion and implication things that a computer has to have spelled out. When the Linrg tool refers to the local variable slope, for example we cared only that the name slope should consistently refer to the result of a particular calculation; the central processor of a computer running Linrg, however, cares about the amount of memory allocated to slope, the format by which it is interpreted, how memory is reserved for the use of slope and later released, that the memory should be aligned on the proper address boundary, that no conflicting use be made of that memory, and, finally, precisely how the address of slope is to be determined when data is to be stored or retrieved there. The same issues have to be resolved for each and every named thing in a program.