Example of JSON parsing using jsmn

json-parsing-example.c

/**
 * Extract the string value of a JSON key out of a parsed JSON structure.
 * 
 * @param json Generic JSON stateful structure as returned/modified by JSMN library
 * @param name Null-terminated string with key name to lookup
 * @param json_val This string pointer will be updated with the location of the data in the JSON buffer.
 *
 * @return -1 if no key found, otherwise we return the length of the string 
 *     (excluding NULL-terminator; just like strlen() would return).
 *
*/
int json_get_key_value(json_stateful_t *json, char *name, int length, char** json_val)

    // Do stuff (probably loop through `json` member elements)
    
     if ( strncmp(name, &json[key.start], length) == 0) {
        jsmntok_t value_key = tokens[i + 1];
        unsigned int value_length = value_key.end - value_key.start;
        *json_val = json + value_key.start;
        sprintf(print_buf, "test result %i ",value_key.start);
        HalUARTWrite(HAL_UART_PORT_0,(uint8 *)print_buf, strlen(print_buf));
        
        return value_length;
    }
    
    // Check everything else.  Nothing matches
    return -1;
}

// Use the stuff
#define JSON_BUFFER_LEN 512      // Half-kB buffer
char json_buffer[JSON_BUFFER_LEN];
int main(void) {
    
    // Read JSON data (simplified to a blocking function)
    uart_read_json(json_buffer);
    
    // Parse JSON
    json_stateful_t json;
    json_parse_string(&json, json_buffer);
    
    // Get a key-value
    char *wifi_ssid;
    int wifi_ssid_len;
    
    if ((wifi_ssid_len = json_get_key_value(&json, "wifi_ssid", strlen("wifi_ssid"), &wifi_ssid)) < 0 ) {
        // Error
    }
    
    // Make use of wifi_name.
}