Phase 2: Preprocessing a C++ Program
In Phase 2, you give the command to compile the program (Fig. 1.2). In a C++ system, a preprocessor program executes automatically before the compiler’s translation phase begins (so we call preprocessing Phase 2 and compiling Phase 3). The C++ preprocessor obeys commands called preprocessing directives, which indicate that certain manipulations are to be performed on the program before compilation. These manipulations usually include other text files to be compiled, and perform various text replacements. The most common preprocessing directives are discussed in the early chapters; a detailed discussion of preprocessor features appears in Appendix E, Preprocessor.