jsmn_parse in loop results: Object expected Error

[forest-roby]

Dear All,
I am playing with JSMN for the first time. It is working for my purposes but I would like to run it in a loop, continouly updating information.
When I run the function for the first time everything works, after that in each loop I receive: Object expected error message.
here is the code: (you have to get your own api key )

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <curl/curl.h>
#include <conio.h>
#include <jsmn.h>

struct memory{
	char* memory;
	size_t size;
};

static size_t writecallback(char* contents, size_t size, size_t nmemb, void *userp){
	
	size_t realsize = size * nmemb;
	struct memory* mem = (struct memory*)userp;

	char *ptr = (char*) realloc(mem->memory, mem->size + realsize + 1); //VC++ miatt kell a (char*) a realloc elé.
	if (ptr == NULL)
		return(0);

	mem->memory = ptr;
	memcpy(&mem->memory[mem->size], contents, realsize);
	mem->size += realsize;
	mem->memory[mem->size] = 0;
	return realsize;

	//fprintf(stderr, "\r%s", contents);
	//fflush(stdout);
	//return size * nmemb;
}

//jsmn
static const char *JSON_STRING = "";

static int jsoneq(const char* json, jsmntok_t* tok, const char* s) {
	if (tok->type == JSMN_STRING && (int)strlen(s) == tok->end - tok->start &&
		strncmp(json + tok->start, s, tok->end - tok->start) == 0) {
		return 0;
	}
	return -1;
}
//JSMN vége


int get_coordinates(double *lat, double *lon, double *alt, double *azi, double *ele, double *_ra, double *_dec, long long *_times) {

	CURL* curl;
	CURLcode res;
	struct memory chunk;

	chunk.memory = NULL;
	chunk.size = 0;
	curl_global_init(CURL_GLOBAL_ALL);

	//jsmn rész
	int i = 0;
	int r = -1;
	jsmn_parser p;
	jsmntok_t t[500]; /* We expect no more than 128 tokens */
	//jsmn rész vége


	curl = curl_easy_init();
	if (curl) {
		curl_easy_setopt(curl, CURLOPT_URL, "https://www.n2yo.com/rest/v1/satellite/positions/25544/46.3185/17.7515/0/1/&apiKey=*HERE IS MY KEY*");
		curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writecallback);
		curl_easy_setopt(curl, CURLOPT_WRITEDATA, &chunk);

		res = curl_easy_perform(curl);
		if (res != CURLE_OK) {
			fprintf(stderr, "curl_easy_perform() returned %s\n",
				curl_easy_strerror(res));
		}
		else {
			//Itt töltöttük le az adatokat:
			//printf("We got %d bytes to our callback. We received the following text:\n\n", (int)chunk.size);
			printf("%s\n\n", chunk.memory);
			//
			//	JSMN próba
			//
			static const char* JSON_STRING = chunk.memory;

			jsmn_init(&p);
			r = jsmn_parse(&p, JSON_STRING, strlen(JSON_STRING), t,
				sizeof(t) / sizeof(t[0]));
			if (r < 0) {
				printf("Failed to parse JSON: %d\n", r);
				return 1;
			}

			/* Assume the top-level element is an object */
			if (r < 1 || t[0].type != JSMN_OBJECT) {
				printf("Object expected\n");
				//printf("%d\n", r);
				//printf("%d\n", t[0]);
				return 1;
			}

			/* Loop over all keys of the root object */
			for (i = 1; i < r; i++) {
				if (jsoneq(JSON_STRING, &t[i], "user") == 0) {
					/* We may use strndup() to fetch string value */
					printf("- User: %.*s\n", t[i + 1].end - t[i + 1].start,
						JSON_STRING + t[i + 1].start);
					i++;
				}
				else if (jsoneq(JSON_STRING, &t[i], "admin") == 0) {
					/* We may additionally check if the value is either "true" or "false" */
					printf("- Admin: %.*s\n", t[i + 1].end - t[i + 1].start,
						JSON_STRING + t[i + 1].start);
					i++;
				}
				else if (jsoneq(JSON_STRING, &t[i], "uid") == 0) {
					/* We may want to do strtol() here to get numeric value */
					printf("- UID: %.*s\n", t[i + 1].end - t[i + 1].start,
						JSON_STRING + t[i + 1].start);
					i++;
				}
				else if (jsoneq(JSON_STRING, &t[i], "groups") == 0) {
					int j;
					printf("- Groups:\n");
					if (t[i + 1].type != JSMN_ARRAY) {
						continue; /* We expect groups to be an array of strings */
					}
					for (j = 0; j < t[i + 1].size; j++) {
						jsmntok_t* g = &t[i + j + 2];
						printf("  * %.*s\n", g->end - g->start, JSON_STRING + g->start);
					}
					i += t[i + 1].size + 1;
				}
				else {
					//
					//printf("%.*s, i: %d\n", t[i].end - t[i].start, JSON_STRING + t[i].start, i);
					//strncpy_s(tomb, t[i].end - t[i].start, JSON_STRING + t[i].start, t[i].end - t[i].start);
				}
			}
			//printf("% .*s: % .*s\n", t[1].end - t[1].start, JSON_STRING + t[1].start, t[2].end - t[2].start, JSON_STRING + t[2].start);
			//printf("% .*s: % .*s\n", t[5].end - t[5].start, JSON_STRING + t[5].start, t[6].end - t[6].start, JSON_STRING + t[6].start );
			//printf("% .*s: % .*s\n", t[7].end - t[7].start, JSON_STRING + t[7].start, t[8].end - t[8].start, JSON_STRING + t[8].start);

			sscanf_s((JSON_STRING + t[13].start), "%lf", lat);
			sscanf_s((JSON_STRING + t[15].start), "%lf", lon);
			sscanf_s((JSON_STRING + t[17].start), "%lf", alt);
			sscanf_s((JSON_STRING + t[19].start), "%lf", azi);
			sscanf_s((JSON_STRING + t[21].start), "%lf", ele);
			sscanf_s((JSON_STRING + t[23].start), "%lf", _ra);
			sscanf_s((JSON_STRING + t[25].start), "%lf", _dec);
			sscanf_s((JSON_STRING + t[27].start), "%d", _times);

			//
			//JSMN vége
			//
		}

		free(chunk.memory);
		curl_easy_cleanup(curl);

	}
	curl_global_cleanup();


return(0);
};





int main(void) {

	double latitude, longitude, altitude, azimuth, elevation, ra, dec;
	long long timestamp;
	int c = 1;

	//-------------------------------------------------------------------
		while (c != 'n')             // until correct key is pressed
		{
			do {                    // forever
				//do
	//
	get_coordinates(&latitude, &longitude, &altitude, &azimuth, &elevation, &ra, &dec, &timestamp);
	printf("\nLatitude:\t%lf", latitude);
	printf("\nLongitude:\t%lf", longitude);
	printf("\nAltitude:\t%lf", altitude);
	printf("\nAzimuth:\t%lf", azimuth);
	printf("\nElevation:\t%lf", elevation);
	printf("\nRa:\t\t%lf", ra);
	printf("\nDec:\t\t%lf", dec);
	printf("\nTimestamp:\t%ld", timestamp);
	printf("\n");
	//-------------------------------------------------------------------
			//do
			} while (!_kbhit());      // until a key press detected
			c = _getch();            // fetch that key press
		}
	//

	return(0);
}

(Visual Studio 2019, windows 10)

The received text looks like this:
{"info":{"satname":"SPACE STATION","satid":25544,"transactionscount":91},"positions":[{"satlatitude":-51.79721854,"satlongitude":-12.7783,"sataltitude":439.3,"azimuth":198.83,"elevation":-49.23,"ra":316.23335672,"dec":-77.09388627,"timestamp":1577393729}]}

I learned to program in C about 15 years ago in Linux - I was quite good at it and never used it since. I am sure the code is not elegant. First I want it to work.
I appreciate any help you can provide.

Robert

[forest-roby]

I was too hasty asking your help!
Farther bugging showed the error. Problem was with: JSON_STRING
This change helped:

static const char* JSON_STRING = NULL;
JSON_STRING = chunk.memory;