Remember the problem about a negative or too large "repeat" value in Section 2, “Other types of options”? The code that prints the greeting has those lines:

...
repeat = cfg_getint(cfg_greet, "repeat");
while(repeat--)
...
        

The repeat variable is defined as an int, a signed integer. If the user specified a negative repeat value in the configuration file, this code would continue to decrease the repeat variable until it eventually underflowed.

We'll fix this by not allowing a negative value in the configuration file. Of course we could first just check if the value is negative and then abort, using cfg_getint() and a test. But we will use a validating callback function instead. This way cfg_parse() will return an error directly when parsing the file, additionally indicating on which line the error is.

A validating callback function is defined as:

typedef int (*cfg_validate_callback_t)(cfg_t *cfg, cfg_opt_t *opt);
        

This function takes two arguments: the section and the option. It should return 0 on success (ie, the value validated ok). All other values indicates an error, and the parsing is aborted. The callback function should notify the error itself, for example by calling cfg_error().

Here is the code for the callback function:

1	int validate_unsigned_int(cfg_t *cfg, cfg_opt_t *opt)
2	{
3	    int value = cfg_opt_getnint(opt, cfg_opt_size(opt) - 1);
4	    if(value < 0)
5	    {
6	        cfg_error(cfg, "integer option '%s' must be positive in section '%s'",
7	                opt->name, cfg->name);
8	        return -1;
9	    }
10	    return 0;
11	}
12	

Only the last value is validated, because libConfuse will call this function once for every value corresponding to the option. Since the "repeat" option is not a list, we could instead have used cfg_opt_getint(opt) to retrieve the only value. However, if we later want to use this callback to validate an integer list, it is already lists-aware.

1	#include <stdio.h>
2	#include <confuse.h>
3	
4	int validate_unsigned_int(cfg_t *cfg, cfg_opt_t *opt)
5	{
6	    int value = cfg_opt_getnint(opt, cfg_opt_size(opt) - 1);
7	    if(value < 0)
8	    {
9	        cfg_error(cfg, "integer option '%s' must be positive in section '%s'",
10	                opt->name, cfg->name);
11	        return -1;
12	    }
13	    return 0;
14	}
15	
16	int main(void)
17	{
18	    cfg_opt_t greet_opts[] =
19	    {
20	        CFG_STR_LIST("targets", "{World}", CFGF_NONE),
21	        CFG_INT("repeat", 1, CFGF_NONE),
22	        CFG_END()
23	    };
24	    cfg_opt_t opts[] =
25	    {
26	        CFG_SEC("greeting", greet_opts, CFGF_TITLE | CFGF_MULTI),
27	        CFG_END()
28	    };
29	    cfg_t *cfg, *cfg_greet;
30	    int repeat;
31	    int i, j;
32	
33	    cfg = cfg_init(opts, CFGF_NONE);
34	    cfg_set_validate_func(cfg, "greeting|repeat", validate_unsigned_int);
35	    if(cfg_parse(cfg, "hello.conf") == CFG_PARSE_ERROR)
36	        return 1;
37	
38	    for(j = 0; j < cfg_size(cfg, "greeting"); j++)
39	    {
40	        cfg_greet = cfg_getnsec(cfg, "greeting", j);
41	
42	        repeat = cfg_getint(cfg_greet, "repeat");
43	        while(repeat--)
44	        {
45	            printf("%s", cfg_title(cfg_greet));
46	            for(i = 0; i < cfg_size(cfg_greet, "targets"); i++)
47	                printf(", %s", cfg_getnstr(cfg_greet, "targets", i));
48	            printf("!\n");
49	        }
50	    }
51	
52	    cfg_free(cfg);
53	    return 0;
54	}
55