Advanced Programming in the UNIX® Environment

ptg10805159

662 Advanced IPC Chapter 17

return;

}

}

log_quit("can’t find client entry for fd %d", fd);

}

Figure 17.27Functions to manipulateclientarray

The first timeclient_addis called, it callsclient_alloc,which in turn calls

mallocto allocate space for ten entries in the array.After these ten entries areall in

use, a later call toclient_addcausesreallocto allocate additional space. By

dynamically allocating space this way, we have not limited the size of theclientarray

at compile time to some value that we guessed and put into a header.These functions

call thelog_functions (Appendix B) if an error occurs, since we assume that the server

is a daemon.

Normally the server will run as a daemon, but we want to provide an option that

allows it to be run in the foreground, with diagnostic messages sent to the standard

error.This should make the server easier to test and debug, especially if we don’t have

permission to read the log file wherethe diagnostic messages arenormally written.

We’ll use a command-line option to control whether the server runs in the foreground

or as a daemon in the background.

It is important that all commands on a system follow the same conventions, because

this makes them easier to use. If someone is familiar with the way command-line

options areformed with one command, it would create morechances for mistakes if

another command followed different conventions.

This problem is sometimes visible when dealing with white space on the command

line. Some commands requirethat an option be separated from its argument by white

space, but other commands requirethe argument to follow immediately after its option,

without any intervening spaces.Without a consistent set of rules to follow,users either

have to memorize the syntax of all commands or resort to a trial-and-error process

when invoking them.

The Single UNIX Specification includes a set of conventions and guidelines that

promote consistent command-line syntax. They include such suggestions as ‘‘Restrict

each command-line option to a single alphanumeric character’’ and ‘‘All options should

be preceded by a−character.’’

Luckily,the getopt function exists to help command developers process

command-line options in a consistent manner.

#include <unistd.h>

int getopt(intargc,char * const argv[], const char *options);

extern int optind, opterr, optopt;

extern char *optarg;

Returns: the next option character,or

−1when all options have been processed