Difficulty in reading values from an array - c++

Question

I am writing a C++ code and I am struggling with something rather simple:
I have declared an array
uint8_t *received_data as global variable in my code.
Then I allocate its memory inside a function:
void advertisementCallback(const Gap::AdvertisementCallbackParams_t *params) {
if(params->type == 3){
for(int i = 0; i < params->advertisingDataLen; i++){
if(params->advertisingData[i] == 0x16){
if(params->advertisingData[i+1] == 0x34 && params->advertisingData[i+2] == 0x23){
received_data_size = params->advertisingDataLen - (i + 3);
received_data = new uint8_t[received_data_size];
for(int index = i+3; index < params->advertisingDataLen; index++){
received_data[index] = params->advertisingData[index];
//printf("%02x ", received_data[index]);//params->advertisingData[index]);
//printf("\r\n");
}
}
}
}
}
}
Note that the commented printf's are printing the data I receive correctly.
But then in my main when I try the same printf I receive garbage most of the times and some times I receive the last three elements of the array in the first three places and then garbage.
My main is:
int main(void)
{
BLE& ble = BLE::Instance(BLE::DEFAULT_INSTANCE);
ble.init(bleInitComplete);
bool state = true;
while(true){
ble.waitForEvent();
measurement[2]++;
printf("In the loop \n");
for(int i = 0; i < received_data_size; i++){
printf("%02x ", received_data[i]);//params->advertisingData[index]);
printf("\r\n");
}
delete[] received_data;
}
}
The whole code as of now is:
#include "mbed.h"
#include "ble/BLE.h"
/* Optional: Device Name, add for human read-ability */
const static char DEVICE_NAME[] = "G4";
uint16_t uuid16_list[] = {0x2334};
/* You have up to 26 bytes of advertising data to use. */
const static uint8_t AdvData[] = {0x01,0x02,0x03,0x04,0x05}; /* Example of hex data */
uint8_t meas = 0;
uint8_t received_data_size;
static uint8_t *received_data;
uint8_t measurement[] = {0x34,0x23, meas};
/* Optional: Restart advertising when peer disconnects */
void disconnectionCallback(const Gap::DisconnectionCallbackParams_t *params)
{
BLE::Instance().gap().startAdvertising();
}
/**
* This function is called when the ble initialization process has failed
*/
void onBleInitError(BLE &ble, ble_error_t error)
{
/* Avoid compiler warnings */
(void) ble;
(void) error;
/* Initialization error handling should go here */
}
void advertisementCallback(const Gap::AdvertisementCallbackParams_t *params) {
if(params->type == 3){
for(int i = 0; i < params->advertisingDataLen; i++){
if(params->advertisingData[i] == 0x16){
if(params->advertisingData[i+1] == 0x34 && params->advertisingData[i+2] == 0x23){
received_data_size = params->advertisingDataLen - (i + 3);
received_data = new uint8_t[received_data_size];
for(int index = i+3; index < params->advertisingDataLen; index++){
received_data[index] = params->advertisingData[index];
//printf("%02x ", received_data[index]);//params->advertisingData[index]);
//printf("\r\n");
}
}
}
}
}
}
/**
* Callback triggered when the ble initialization process has finished
*/
void bleInitComplete(BLE::InitializationCompleteCallbackContext *params)
{
BLE& ble = params->ble;
ble_error_t error = params->error;
if (error != BLE_ERROR_NONE) {
/* In case of error, forward the error handling to onBleInitError */
onBleInitError(ble, error);
return;
}
/* Ensure that it is the default instance of BLE */
if(ble.getInstanceID() != BLE::DEFAULT_INSTANCE) {
return;
}
/* Set device name characteristic data */
ble.gap().setDeviceName((const uint8_t *) DEVICE_NAME);
/* Optional: add callback for disconnection */
ble.gap().onDisconnection(disconnectionCallback);
/* Sacrifice 3B of 31B to Advertising Flags */
ble.gap().accumulateAdvertisingPayload(GapAdvertisingData::BREDR_NOT_SUPPORTED | GapAdvertisingData::LE_GENERAL_DISCOVERABLE );
ble.gap().setAdvertisingType(GapAdvertisingParams::ADV_CONNECTABLE_UNDIRECTED);
/* Sacrifice 2B of 31B to AdvType overhead, rest goes to AdvData array you define */
//ble.gap().accumulateAdvertisingPayload(GapAdvertisingData::MANUFACTURER_SPECIFIC_DATA, AdvData, sizeof(AdvData));
ble.gap().accumulateAdvertisingPayload(GapAdvertisingData::SERVICE_DATA, measurement, sizeof(measurement));
ble.gap().accumulateAdvertisingPayload(GapAdvertisingData::COMPLETE_LIST_16BIT_SERVICE_IDS, (uint8_t *)uuid16_list, sizeof(uuid16_list));
/* Optional: Add name to device */
ble.gap().accumulateAdvertisingPayload(GapAdvertisingData::COMPLETE_LOCAL_NAME, (uint8_t *)DEVICE_NAME, sizeof(DEVICE_NAME));
/* Set advertising interval. Longer interval == longer battery life */
ble.gap().setAdvertisingInterval(500); /* 100ms */
/* Start advertising */
//ble.gap().startAdvertising();
/*Start Scanning*/
ble.gap().setScanParams(500 /* scan interval */, 200 /* scan window */);
ble.gap().startScan(advertisementCallback);
}
int main(void)
{
BLE& ble = BLE::Instance(BLE::DEFAULT_INSTANCE);
ble.init(bleInitComplete);
bool state = true;
while(true){
ble.waitForEvent();
measurement[2]++;
printf("In the loop \n");
for(int i = 0; i < received_data_size; i++){
printf("%02x ", received_data[i]);//params->advertisingData[index]);
printf("\r\n");
}
delete[] received_data;
}
}
BLE stands for bluetooth low energy. The code is based on examples found at mbed.org
I guess I am missing something, but I am not sure what exactly. Thank you very much for your help.

Answer 1

First of all, without taking a further look at the rest of the code, the first three bytes of your global received_data will never be written. Take a look into this particular part of your advertisementCallback():
for(int index = i+3; index < params->advertisingDataLen; index++){
received_data[index] = params->advertisingData[index];
So the index used for writing to received_data always starts at an offset of 3 - never less - , while it should start at 0. Add a dedicated index variable for this purpose. In your main(), you created a loop starting at 0:
for(int i = 0; i < received_data_size; i++){
printf("%02x ", received_data[i]);
Therefore the first three bytes of your debug output will always contain random data.