Are there simple examples of how to parse a simple JSON file using the C-based YAJL library? - iphone

Question

I know there is an Objective-C wrapper around YAJL, but this is a really fat thing which blows up the whole JASON parser to a ridiculous huge amount of 21 files, many of them with tiny scroll bars.
So to keep my app binary small I'd like to stick with the C-version of that parser. But I'm having a hard time finding any useful documentation for this rather than the wrapper.
Maybe someone who used the C-base can point out such a tutorial or documentation?

Answer 1

The documentation with C examples can be found here: http://lloyd.github.com/yajl/
The github repository with examples can be found here : https://github.com/lloyd/yajl
Here is a C example that reformats JSON from stdin:
#include <yajl/yajl_parse.h>
#include <yajl/yajl_gen.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static int reformat_null(void * ctx)
{
yajl_gen g = (yajl_gen) ctx;
return yajl_gen_status_ok == yajl_gen_null(g);
}
static int reformat_boolean(void * ctx, int boolean)
{
yajl_gen g = (yajl_gen) ctx;
return yajl_gen_status_ok == yajl_gen_bool(g, boolean);
}
static int reformat_number(void * ctx, const char * s, size_t l)
{
yajl_gen g = (yajl_gen) ctx;
return yajl_gen_status_ok == yajl_gen_number(g, s, l);
}
static int reformat_string(void * ctx, const unsigned char * stringVal,
size_t stringLen)
{
yajl_gen g = (yajl_gen) ctx;
return yajl_gen_status_ok == yajl_gen_string(g, stringVal, stringLen);
}
static int reformat_map_key(void * ctx, const unsigned char * stringVal,
size_t stringLen)
{
yajl_gen g = (yajl_gen) ctx;
return yajl_gen_status_ok == yajl_gen_string(g, stringVal, stringLen);
}
static int reformat_start_map(void * ctx)
{
yajl_gen g = (yajl_gen) ctx;
return yajl_gen_status_ok == yajl_gen_map_open(g);
}
static int reformat_end_map(void * ctx)
{
yajl_gen g = (yajl_gen) ctx;
return yajl_gen_status_ok == yajl_gen_map_close(g);
}
static int reformat_start_array(void * ctx)
{
yajl_gen g = (yajl_gen) ctx;
return yajl_gen_status_ok == yajl_gen_array_open(g);
}
static int reformat_end_array(void * ctx)
{
yajl_gen g = (yajl_gen) ctx;
return yajl_gen_status_ok == yajl_gen_array_close(g);
}
static yajl_callbacks callbacks = {
reformat_null,
reformat_boolean,
NULL,
NULL,
reformat_number,
reformat_string,
reformat_start_map,
reformat_map_key,
reformat_end_map,
reformat_start_array,
reformat_end_array
};
static void
usage(const char * progname)
{
fprintf(stderr, "%s: reformat json from stdin\n"
"usage: json_reformat [options]\n"
" -m minimize json rather than beautify (default)\n"
" -u allow invalid UTF8 inside strings during parsing\n",
progname);
exit(1);
}
int
main(int argc, char ** argv)
{
yajl_handle hand;
static unsigned char fileData[65536];
/* generator config */
yajl_gen g;
yajl_status stat;
size_t rd;
int retval = 0;
int a = 1;
g = yajl_gen_alloc(NULL);
yajl_gen_config(g, yajl_gen_beautify, 1);
yajl_gen_config(g, yajl_gen_validate_utf8, 1);
/* ok. open file. let's read and parse */
hand = yajl_alloc(&callbacks, NULL, (void *) g);
/* and let's allow comments by default */
yajl_config(hand, yajl_allow_comments, 1);
/* check arguments.*/
while ((a < argc) && (argv[a][0] == '-') && (strlen(argv[a]) > 1)) {
unsigned int i;
for ( i=1; i < strlen(argv[a]); i++) {
switch (argv[a][i]) {
case 'm':
yajl_gen_config(g, yajl_gen_beautify, 0);
break;
case 'u':
yajl_config(hand, yajl_dont_validate_strings, 1);
break;
default:
fprintf(stderr, "unrecognized option: '%c'\n\n",
argv[a][i]);
usage(argv[0]);
}
}
++a;
}
if (a < argc) {
usage(argv[0]);
}
for (;;) {
rd = fread((void *) fileData, 1, sizeof(fileData) - 1, stdin);
if (rd == 0) {
if (!feof(stdin)) {
fprintf(stderr, "error on file read.\n");
retval = 1;
}
break;
}
fileData[rd] = 0;
stat = yajl_parse(hand, fileData, rd);
if (stat != yajl_status_ok) break;
{
const unsigned char * buf;
size_t len;
yajl_gen_get_buf(g, &buf, &len);
fwrite(buf, 1, len, stdout);
yajl_gen_clear(g);
}
}
stat = yajl_complete_parse(hand);
if (stat != yajl_status_ok) {
unsigned char * str = yajl_get_error(hand, 1, fileData, rd);
fprintf(stderr, "%s", (const char *) str);
yajl_free_error(hand, str);
retval = 1;
}
yajl_gen_free(g);
yajl_free(hand);
return retval;
}