Access violation when getting network adapters with GetAdaptersAddresses in C - c

Question

I don't know if the code from https://learn.microsoft.com/en-us/windows/desktop/api/iphlpapi/nf-iphlpapi-getadaptersaddresses is wrong but when I try to use it in my C project I keep getting the infamous
Access violation reading location 0xFFFFFFFFFFFFFFFF
I have tried increasing the buffer size but nothing seems to fix it. I think this happens after the first adapter is passed through the loop.
#include <stdio.h>
#include <string.h>
#include <locale.h>
#include <winsock2.h>
#include <iptypes.h>
#include <iphlpapi.h>
#include <windows.h>
#pragma comment(lib, "IPHLPAPI.lib")
#define MALLOC(x) HeapAlloc(GetProcessHeap(), 0, (x))
#define FREE(x) HeapFree(GetProcessHeap(), 0, (x))
FILE* fLog = NULL;
void netinfo() {
PIP_ADAPTER_ADDRESSES pAddresses = NULL;
PIP_ADAPTER_ADDRESSES pCurrAddresses = NULL;
DWORD dwRetVal = 0;
ULONG outBufLen = 15000;
ULONG iter = 0;
do {
pAddresses = (IP_ADAPTER_ADDRESSES*)MALLOC(outBufLen);
if (pAddresses == NULL) {
fwprintf(fLog, L"MALLOC error");
break;
dwRetVal = GetAdaptersAddresses(
AF_UNSPEC,
GAA_FLAG_INCLUDE_PREFIX,
NULL,
pAddresses,
&outBufLen
);
if (dwRetVal == ERROR_BUFFER_OVERFLOW) {
FREE(pAddresses);
pAddresses = NULL;
fwprintf(fLog, L"GetAdaptersAddresses() error");
} else {
break;
}
iter++;
}
} while ((dwRetVal == ERROR_BUFFER_OVERFLOW) && (iter < 3));
wchar_t netAddressLog[256];
if (dwRetVal == NO_ERROR && pAddresses != NULL) {
pCurrAddresses = pAddresses;
while (pCurrAddresses) {
// this is where the debugger stops !!!
swprintf(netAddressLog, 256, L"Index: %u", pCurrAddresses->IfIndex);
fwprintf(fLog, netAddressLog);
pCurrAddresses = pCurrAddresses->Next;
}
} else {
fwprintf(fLog, L"GetAdaptersAddresses() error");
}
if (pAddresses) {
FREE(pAddresses);
}
}
int main(int argc, char **argv) {
errno_t error = _wfopen_s(&fLog, L"log.txt", L"a+");
netinfo();
fclose(fLog);
}
So, when trying to access pCurrAddresses->IfIndex it's where the program fails, after the first loop (in which it logs some weird large number for index). I am trying to compare mi slightly modified code to the one from MSDN but I can't figure it out.
I know my code needs better organization but for now this is a blocker

Answer 1

There is some problem in the while loop block:
do {
pAddresses = (IP_ADAPTER_ADDRESSES*)MALLOC(outBufLen);
if (pAddresses == NULL) {
fwprintf(fLog, L"MALLOC error");
break;
/* a } is missing here*/
dwRetVal = GetAdaptersAddresses(
AF_UNSPEC,
GAA_FLAG_INCLUDE_PREFIX,
NULL,
pAddresses,
&outBufLen
);
if (dwRetVal == ERROR_BUFFER_OVERFLOW) {
FREE(pAddresses);
pAddresses = NULL;
fwprintf(fLog, L"GetAdaptersAddresses() error");
} else {
break;
}
iter++;
}
} while ((dwRetVal == ERROR_BUFFER_OVERFLOW) && (iter < 3));
The good corrected code could be:
do {
pAddresses = (IP_ADAPTER_ADDRESSES*)MALLOC(outBufLen);
if (pAddresses == NULL) {
fwprintf(fLog, L"MALLOC error");
break;
}
dwRetVal = GetAdaptersAddresses(
AF_UNSPEC,
GAA_FLAG_INCLUDE_PREFIX,
NULL,
pAddresses,
&outBufLen
);
if (dwRetVal == ERROR_BUFFER_OVERFLOW) {
FREE(pAddresses);
pAddresses = NULL;
fwprintf(fLog, L"GetAdaptersAddresses() error");
} else {
break;
}
iter++;
} while ((dwRetVal == ERROR_BUFFER_OVERFLOW) && (iter < 3));