Browse Source Download (without any required ccan dependencies)

Module:

autodata

Summary:

stash pointers in your binary for automatic registration

Dependencies:

Description:

This code allows declarations in your source which you can gather together at runtime to form tables. This is often used in place of having a central registration function or table.

Note that this technique does not work in general for shared libaries, only for code compiled into a binary.

Example:

// Distributed commandline option registration (note: ccan/opt is better!)
#include <ccan/autodata/autodata.h>
#include <stdio.h>
#include <unistd.h>
#include <stdbool.h>
#include <err.h>

static bool verbose = false;

// This would normally be in a header, so any C file can use it.
struct option {
     char c;
     bool takes_arg;
     bool (*cb)(char *optarg);
};
AUTODATA_TYPE(options, struct option);
#define REGISTER_OPTION(optstruct) \
             AUTODATA(options, (optstruct))

// Now a few examples (could be anywhere in source)
static bool verbose_cb(char *unused)
{
     verbose = true;
     return true;
}
static struct option dash_v = { 'v', false, verbose_cb };
REGISTER_OPTION(&dash_v);

static bool chdir_cb(char *dir)
{
     if (verbose)
             printf("chdir to %s. ", dir);
     if (chdir(dir) != 0)
             return false;
     return true;
}
static struct option dash_C = { 'C', true, chdir_cb };
REGISTER_OPTION(&dash_C);

int main(int argc, char *argv[])
{
     struct option **opts;
     size_t i, num;
     int o;
     char *optstring, *p;

     // Gather together all the registered options.
     opts = autodata_get(options, &num);

     // Make pretty string for getopt().
     p = optstring = malloc(num * 2 + 1);
     for (i = 0; i < num; i++) {
             *(p++) = opts[i]->c;
             if (opts[i]->takes_arg)
                     *(p++) = ':';
     }
     *p = '\0';

     while ((o = getopt(argc, argv, optstring)) != -1) {
             if (o == '?')
                     exit(1);
             // Call callback in matching option.
             for (i = 0; i < num; i++) {
                     if (opts[i]->c == o) {
                             if (!opts[i]->cb(optarg))
                                     err(1, "parsing -%c", o);
                             break;
                     }
             }
     }
     // free up gathered option table.
     autodata_free(opts);

     if (verbose)
             printf("verbose mode on\n");
     return 0;
}
// Given -v outputs 'verbose mode on'
// Given -v -C / outputs 'chdir to /. verbose mode on'

License:

BSD-MIT