C Primer Plus®, Third Edition

Manifest Constants: #define

The #define preprocessor directive, like all preprocessor directives, begins with a # symbol. The ANSI standard permits the # symbol to be preceded by spaces or tabs, and it allows for space between the # and the remainder of the directive. Older versions of C, however, typically require that the directive begin in the leftmost column and that there be no spaces between the # and the remainder of the directive. A directive can appear anywhere in the source file, and the definition holds from its place of appearance to the end of the file. We have used directives heavily to define symbolic, or manifest, constants in our programs, but they have more range than that, as we will show. Listing 16.1 illustrates some ...