Managing error strings in C

[Dan Salomon]

In article <1991Jan10.122227 at lotus.lotus.com> blambert at lotus.lotus.com (Brian Lambert) writes:
>Hi:
>
>I was wondering if anyone out there had any clever ways of handling
>error messages in C.  That is, in small/medimum size programs one
>usually winds up with all sorts of:
>
>    PrintLog("Memory allocation error");
>
>lines in the program.  I have seen code where people define an array of
>char pointers to error messages used in the program such as:
>
>    char *errors[] = {
>        "Memory allocation error",
>        "Can't open file",
>        ...
>    };
>
>    #define NO_MEMORY    0
>    #define CANT_OPEN    1

One method that worked fairly well for me was to write an error
message preprocessor program.  The error messages are stored in
an easy to maintain data file, and a program generates .h files
from that data file.   I.e:

		-------------------
		|  Error message  |
		|  data file      |
		|  "errors.dat"   |
		-------------------
			|
			V
			|
		-------------------
		|  Error message  |
		|  preprocessor   |
		-------------------
	       /                   \ 
	      /                     \ 
	     /                       \
    -------------------       -------------------
    |   Error code    |       |  Error message  |
    | definition file |       |  init file      |
    |  "err_codes.h"  |       |  "err_mess.h"   |
    -------------------       -------------------

The files will look something like the following:

errors.dat
----------
NO_MEMORY  "Memory allocation error"
CANT_OPEN  "Can't open file"
  ...          ...

err_codes.h
-----------
#define NO_MEMORY    0
#define CANT_OPEN    1
   ...

err_mess.h
----------
char *errors[] = {
    "Memory allocation error",
    "Can't open file",
       ...
    };

The preprocessor is trivial to write, since it is just copying strings
from one file to another and maintaining a counter.  The data file is
easy to maintain, since it doesn't need to include all the messy C
punctuation.  A utility like make can be used to rerun the preprocessor
automatically every time the data file is modified.
-- 

Dan Salomon -- salomon at ccu.UManitoba.CA
               Dept. of Computer Science / University of Manitoba
	       Winnipeg, Manitoba, Canada  R3T 2N2 / (204) 275-6682