9.2.1.1 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> BEGIN_C_DECLS 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); END_C_DECLS #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 #if HAVE_CONFIG_H # include <config.h> #endif #include <stdio.h> #include <sys/types.h> #if STDC_HEADERS # include <stdlib.h> # include <string.h> #elif HAVE_STRINGS_H # include <strings.h> #endif /*STDC_HEADERS*/ #if HAVE_UNISTD_H # include <unistd.h> #endif #if HAVE_ERRNO_H # include <errno.h> #endif /*HAVE_ERRNO_H*/ #ifndef errno /* Some systems #define this! */ extern int errno; #endif #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':

#ifndef EXIT_SUCCESS # define EXIT_SUCCESS 0 # define EXIT_FAILURE 1 #endif

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

#if HAVE_CONFIG_H # include <config.h> #endif #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); } void sic_warning (const char *message) { error (-1, "warning", message); } void sic_error (const char *message) { error (-1, "ERROR", message); } void 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; void set_program_name (const char *path) { if (!program_name) program_name = xstrdup (basename (path)); }