Fingerprint calls cause segfaults in c++ - c++

Question

I'm trying to write a simple fingerprint scanning program in c++ using libfprint, however it intermittently segfaults when run. Valgrind says the error is in the call to fp_enroll_finger which is consistent with my debugging, however beyond that I have absolutely no idea what is causing this error. Some of the times the program is run its fine, but some times it seems to consistently segfault for a period of time whenever the program is run?
Heres the code:
#include <iostream>
extern "C"
{
#include <libfprint/fprint.h>
}
using namespace std;
fp_dev * fpdev;
fp_print_data ** fpdata;
bool createDevice();
int main(int argc, char **argv)
{
int r = fp_init();
if(r != 0)
{
return r;
}
while(createDevice())
{
cout << "Scan right index finger" << endl;
int enrollStatus = fp_enroll_finger(fpdev, fpdata);
if(enrollStatus != 1)
{
cout << "Bad scan" << endl;
fp_dev_close(fpdev);
}
else
{
cout << "Good scan" << endl;
fp_print_data_save(fpdata[0], RIGHT_INDEX);
break;
}
}
if(fpdev != NULL)
{
fp_dev_close(fpdev);
}
fp_exit();
return 0;
}
bool createDevice()
{
fp_dscv_dev ** listOfDiscoveredDevs;
fp_dscv_dev * discoveredDevice;
listOfDiscoveredDevs = fp_discover_devs();
discoveredDevice = listOfDiscoveredDevs[0];
if(discoveredDevice != NULL)
{
cout << "Device found" << endl;
fpdev = fp_dev_open(discoveredDevice);
}
else
{
cout << "No device found" << endl;
return false;
}
fp_dscv_devs_free(listOfDiscoveredDevs);
return true;
}

Answer 1

You need to define fpdev and fpdata as:
fp_dev * fpdev;
fp_print_data * fpdata;
And use them as:
fp_enroll_finger(&fpdev, &fpdata);
Also don't forget to free fpdata when you no longer need it with fp_print_data_free
fp_dev * fpdev;
fp_print_data ** fpdata;
Will create 2 uninitialised pointers pointing to random memory location and leading to segfault once fp_enroll_finger will attempt to acces that location.
Checking fp_enroll_finger return value can be useful as well.