Creating a what string

Learn how to create a what string.

The what program searches for a null-terminated string that starts with a special four-character sequence:

@(#)

To include this string in a C-language executable, define a global character-string variable. For example, these source statements produce the two-line what listing above:

char *version_string = "@(#)monet R2.0 Baselevel 1";
char *version_time   = "@(#)Thu Feb 11 17:33:23 EST 2003;

As an alternative, you can generate the time stamp dynamically when the monet program is linked:

1. Create a new source file that contains the statements that define the what strings. Instead of hard-coding a date string, use a cpp(1) macro in the source file. This example uses a source file named version_info.h, which contains a macro named DATE:

   char *version_string = "@(#)monet R2.0 Baselevel 1";
   char *version_time = DATE;

2. Use shell command substitution to incorporate the current time dynamically into the value for the DATE macro:

   SHELL = /bin/sh
   OTHER_OBJS = main.o cmd_line.o                              (and so on)
   monet: version_info.h $(OTHER_OBJS)
      cc -o monet -DDATE="\"@(#)'date'\"" $(OTHER_OBJS)

   A rebuild of monet is also triggered if the version_string variable is edited manually in version_info.h.

   The version_string can be generated dynamically, too (for example, with environment variables). But it is more likely that the project manager edits this string's value before major builds.