1 /* $NetBSD: simple.c,v 1.2 2020/05/25 20:47:24 christos Exp $ */
2
3 #include <stdio.h>
4 #include <string.h>
5 #include "../jsmn.h"
6
7 /*
8 * A small example of jsmn parsing when JSON structure is known and number of
9 * tokens is predictable.
10 */
11
12 const char *JSON_STRING =
13 "{\"user\": \"johndoe\", \"admin\": false, \"uid\": 1000,\n "
14 "\"groups\": [\"users\", \"wheel\", \"audio\", \"video\"]}";
15
jsoneq(const char * json,jsmntok_t * tok,const char * s)16 static int jsoneq(const char *json, jsmntok_t *tok, const char *s) {
17 if (tok->type == JSMN_STRING && (int) strlen(s) == tok->end - tok->start &&
18 strncmp(json + tok->start, s, tok->end - tok->start) == 0) {
19 return 0;
20 }
21 return -1;
22 }
23
main()24 int main() {
25 int i;
26 int r;
27 jsmn_parser p;
28 jsmntok_t t[128]; /* We expect no more than 128 tokens */
29
30 jsmn_init(&p);
31 r = jsmn_parse(&p, JSON_STRING, strlen(JSON_STRING), t, sizeof(t)/sizeof(t[0]));
32 if (r < 0) {
33 printf("Failed to parse JSON: %d\n", r);
34 return 1;
35 }
36
37 /* Assume the top-level element is an object */
38 if (r < 1 || t[0].type != JSMN_OBJECT) {
39 printf("Object expected\n");
40 return 1;
41 }
42
43 /* Loop over all keys of the root object */
44 for (i = 1; i < r; i++) {
45 if (jsoneq(JSON_STRING, &t[i], "user") == 0) {
46 /* We may use strndup() to fetch string value */
47 printf("- User: %.*s\n", t[i+1].end-t[i+1].start,
48 JSON_STRING + t[i+1].start);
49 i++;
50 } else if (jsoneq(JSON_STRING, &t[i], "admin") == 0) {
51 /* We may additionally check if the value is either "true" or "false" */
52 printf("- Admin: %.*s\n", t[i+1].end-t[i+1].start,
53 JSON_STRING + t[i+1].start);
54 i++;
55 } else if (jsoneq(JSON_STRING, &t[i], "uid") == 0) {
56 /* We may want to do strtol() here to get numeric value */
57 printf("- UID: %.*s\n", t[i+1].end-t[i+1].start,
58 JSON_STRING + t[i+1].start);
59 i++;
60 } else if (jsoneq(JSON_STRING, &t[i], "groups") == 0) {
61 int j;
62 printf("- Groups:\n");
63 if (t[i+1].type != JSMN_ARRAY) {
64 continue; /* We expect groups to be an array of strings */
65 }
66 for (j = 0; j < t[i+1].size; j++) {
67 jsmntok_t *g = &t[i+j+2];
68 printf(" * %.*s\n", g->end - g->start, JSON_STRING + g->start);
69 }
70 i += t[i+1].size + 1;
71 } else {
72 printf("Unexpected key: %.*s\n", t[i].end-t[i].start,
73 JSON_STRING + t[i].start);
74 }
75 }
76 return 0;
77 }
78