This is lib/get_num.h (Listing 3-5, page 59), an example from the book, The Linux Programming Interface.

The source code file is copyright 2024, Michael Kerrisk, and is licensed under the GNU Lesser General Public License, version 3.

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In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

  Cover of The Linux Programming Interface
+/* get_num.h
+   Header file for get_num.c.
 #ifndef GET_NUM_H
 #define GET_NUM_H
 #define GN_NONNEG       01      /* Value must be >= 0 */
 #define GN_GT_0         02      /* Value must be > 0 */
                                 /* By default, integers are decimal */
 #define GN_ANY_BASE   0100      /* Can use any base - like strtol(3) */
 #define GN_BASE_8     0200      /* Value is expressed in octal */
 #define GN_BASE_16    0400      /* Value is expressed in hexadecimal */
 long getLong(const char *arg, int flags, const char *name);
 int getInt(const char *arg, int flags, const char *name);

Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.

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