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 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 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