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Back: Portability Infrastructure
Forward: Memory Management
FastBack: A Sample Shell Application
Up: Portability Infrastructure
FastForward: Library Implementation
Top: Autoconf, Automake, and Libtool
Contents: Table of Contents
Index: Index
About: About this document Error Management

A good place to start with any project design is the error management facility. In Sic I will use a simple group of functions to display simple error messages. Here is `sic/error.h':

#ifndef SIC_ERROR_H
#define SIC_ERROR_H 1

#include <sic/common.h>


extern const char *program_name;
extern void set_program_name (const char *argv0);

extern void sic_warning      (const char *message);
extern void sic_error        (const char *message);
extern void sic_fatal        (const char *message);


#endif /* !SIC_ERROR_H */

This header file follows the principles set out in 9.1.2 C Header Files.

I am storing the program_name variable in the library that uses it, so that I can be sure that the library will build on architectures that don't allow undefined symbols in libraries(12).

Keeping those preprocessor macro definitions designed to aid code portability together (in a single file), is a good way to maintain the readability of the rest of the code. For this project I will put that code in `common.h':

#ifndef SIC_COMMON_H
#define SIC_COMMON_H 1

#  include <config.h>

#include <stdio.h>
#include <sys/types.h>

#  include <stdlib.h>
#  include <string.h>
#  include <strings.h>
#endif /*STDC_HEADERS*/

#  include <unistd.h>

#  include <errno.h>
#endif /*HAVE_ERRNO_H*/
#ifndef errno
/* Some systems #define this! */
extern int errno;

#endif /* !SIC_COMMON_H */

You may recognise some snippets of code from the Autoconf manual here--- in particular the inclusion of the project `config.h', which will be generated shortly. Notice that I have been careful to conditionally include any headers which are not guaranteed to exist on every architecture. The rule of thumb here is that only `stdio.h' is ubiquitous (though I have never heard of a machine that has no `sys/types.h'). You can find more details of some of these in section `Existing Tests' in The GNU Autoconf Manual.

Here is a little more code from `common.h':

#  define EXIT_SUCCESS  0
#  define EXIT_FAILURE  1

The implementation of the error handling functions goes in `error.c' and is very straightforward:

#  include <config.h>

#include "common.h"
#include "error.h"

static void error (int exit_status, const char *mode, 
                   const char *message);

static void
error (int exit_status, const char *mode, const char *message)
  fprintf (stderr, "%s: %s: %s.\n", program_name, mode, message);

  if (exit_status >= 0)
    exit (exit_status);

sic_warning (const char *message)
  error (-1, "warning", message);

sic_error (const char *message)
  error (-1, "ERROR", message);

sic_fatal (const char *message)
  error (EXIT_FAILURE, "FATAL", message);

I also need a definition of program_name; set_program_name copies the filename component of path into the exported data, program_name. The xstrdup function just calls strdup, but aborts if there is not enough memory to make the copy:

const char *program_name = NULL;

set_program_name (const char *path)
  if (!program_name)
    program_name = xstrdup (basename (path));

This document was generated by Gary V. Vaughan on February, 8 2006 using texi2html

  Published under the terms of the Open Publication License Design by Interspire